CaltechAUTHORS: Article
https://feeds.library.caltech.edu/people/Pellegrino-S/article.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenThu, 13 Jun 2024 13:46:38 -0700Cable-Stiffened Pantographic Deployable Structures Part 2: Mesh Reflector
https://resolver.caltech.edu/CaltechAUTHORS:YOUaiaaj97
Year: 1997
The general concept of deployable structures based on pantographs that are deployed and stiffened by means of cables is applied to the design of the support structure for a large mesh reflector. The two main components of this structure are a cable-stiffened pantographic ring that deploys and pretensions a cable network that, in turn, provides a series of stiff, geometrically accurate support points to which a reflective wire mesh or flexible membrane would be connected. The pantographic ring is a highly redundant structure with an internal mechanism that permits synchronous deployment without any strain in the rods. The geometric conditions that have to be satisfied in order for an n-sided ring to fold without any strain are investigated, including the effects of joint size. An experimental model has been designed and tested. In the folded configuration, it has a diameter of 0.6 m and height of 1.2 m; in the deployed configuration, it has a diameter of 3.5 m. Stiffness and deployment tests on this model have shown its behavior to be linear and the maximum shape error to be ±0.3 mm.https://resolver.caltech.edu/CaltechAUTHORS:YOUaiaaj97Modeling and Control of a Flexible Structure Incorporating Inertial Slip-Stick Actuators
https://resolver.caltech.edu/CaltechAUTHORS:DARjgcd99
Year: 1999
Shape and vibration control of a linear flexible structure by means of a new type of inertial slip-stick actuator are investigated. A nonlinear model representing the interaction between the structure and a six-degree-of-freedom Stewart platform system containing six actuators is derived, and closed-loop stability and performance of the controlled systems are investigated. A linearized model is also derived for design purposes. Quasistatic alignment of a payload attached to the platform is solved simply by using a proportional controller based on a linear kinematic model. The stability of this controller is examined using a dynamic model of the complete system and is validated experimentally by introducing random thermal elongations of several structural members. Vibration control is solved using an H∞ loop-shaping controller and, although its performance is found to be less satisfactory than desired, the nonlinear model gives good predictions of the performance and stability of the closed-loop system.https://resolver.caltech.edu/CaltechAUTHORS:DARjgcd99Interaction Between Gravity Compensation Suspension System and Deployable Structure
https://resolver.caltech.edu/CaltechAUTHORS:FISjsr00
Year: 2000
DOI: 10.2514/6.1998-1835
Gravity compensation suspension systems are essential to support space structures during tests on Earth, but also impose constraints on the structures that have the effect of changing their behavior. A computational and experimental study of the interaction of a rigid panel solar array model with a manually adjustable suspension system during quasi-static deployment tests in the 1-g environment of the laboratory is presented. A methodology is established for modeling this interaction, for predicting the effects of suspension system adjustments, and for optimization of the suspension system through these adjustments. Some improvements can be achieved by manual adjustments, but further optimization requires an active system.https://resolver.caltech.edu/CaltechAUTHORS:FISjsr00Deployable Tensegrity Reflectors for Small Satellites
https://resolver.caltech.edu/CaltechAUTHORS:TIBjsr02
Year: 2002
Future small satellite missions require low-cost, precision reflector structures with large aperture that can be packaged in a small envelope. Existing furlable reflectors form a compact package which, although narrow, is too tall for many applications.An alternative approach is proposed, consisting of a deployable "tensegrity" prism forming a ring structure that deploys two identical cable nets (front and rear nets) interconnected by tension ties; the reflecting mesh is attached to the front net. The geometric configuration of the structure has been optimized to reduce the compression in the struts of the tensegrity prism. A small-scale physical model has been constructed to demonstrate the proposed concept. A preliminary design of a 3-m-diam, 10-GHz reflector with a focal-length-to-diameter ratio of 0.4 that can be packaged within an envelope of 0.1 x 0.2 x 0.8 m^3 is presented.https://resolver.caltech.edu/CaltechAUTHORS:TIBjsr02Thin-Shell Deployable Reflectors with Collapsible Stiffeners Part 1: Approach
https://resolver.caltech.edu/CaltechAUTHORS:TANaiaa06
Year: 2006
DOI: 10.2514/1.16320
Thin-shell deployable reflector structures that are folded elastically in a nearly inextensional mode have been recently realized, exploiting the recent availability of high-modulus, ultrathin composite materials. An inherent and significant limitation of this approach is that these structures remain "floppy" in their deployed configuration. This paper presents a general concept for increasing the deployed stiffness of such structures, through the addition of a collapsible edge stiffener around the rim of a reflector dish. Ananalytical expression of the frequency/stiffness related to the softest deformation mode of a thin-shell reflector structure is presented, both with and without the stiffener. During folding, the stiffener collapses elastically, and this behavior is facilitated by the introduction of suitable discontinuities within the stiffener, or between the dish and the stiffener. A detailed study of a range of different options is presented, and one particular scheme is selected and optimized. For a specific example, a stiffness increase by a factor of 31 and a fundamental frequency increase by a factor of 4 are achieved, with a mass increase of only 16%.https://resolver.caltech.edu/CaltechAUTHORS:TANaiaa06Space Frames with Multiple Stable Configurations
https://resolver.caltech.edu/CaltechAUTHORS:SCHIaiaaj07
Year: 2007
DOI: 10.2514/1.16825
This paper is concerned with beamlike spaceframes that include a large number of bistable elements, and exploit the bistability of the elements to obtain structures with multiple stable configurations. By increasing the number of bistable elements, structures with a large number of different configurations can be designed. A particular attraction of this approach is that it produces structures able to maintain their shape without any power being supplied. The first part of this paper focuses on the design and realization of a low-cost snap-through strut, whose two different lengths provide the required bistable feature. A parametric study of the length-change of the strut in relation to the peak force that needs to be applied by the driving actuators is carried out. Bistable struts based on this concept have been made by injection molding nylon. Next, beamlike structures based on different architectures are considered. It is shown that different structural architectures produce structures with workspaces of different size and resolution, when made from an identical number of bistable struts. One particular architecture, with 30 bistable struts and hence over 1 billion different configurations, has been demonstrated.https://resolver.caltech.edu/CaltechAUTHORS:SCHIaiaaj07A bistable structural element
https://resolver.caltech.edu/CaltechAUTHORS:SCHIpime08
Year: 2008
DOI: 10.1243/09544062JMES982
This article presents a novel bistable structural element that has high stiffness in stable configurations, but requires only a small amount of energy to be switched from one configuration to the other. The element is based on a planar linkage of four bars connected by revolute joints,
braced by tape-spring diagonals. A description of the concept is presented, along with a detailed theoretical analysis of its mechanical behaviour. Experimental measurements obtained from a prototype structure are found to be in very good agreement with the predictions from this
analytical model.https://resolver.caltech.edu/CaltechAUTHORS:SCHIpime08Systematically Creased Thin-Film Membrane Structures
https://resolver.caltech.edu/CaltechAUTHORS:PAPjsr08
Year: 2008
DOI: 10.2514/1.18285
This paper presents a study of a square membrane, creased according to the Miura-ori folding pattern. When the membrane is allowed to expand from its packaged configuration, it initially expands elastically under zero corner forces. Starting from this naturally expanded configuration, the paper investigates the stress distribution and the load-displacement relationship when in-plane, diagonal loads are applied at the corners. It is found that out-of-plane bending is the main load-carrying mode and, for stress magnitudes typical of current solar-sail designs, the behavior of the membrane remains linear elastic. A simple analytical model, originally proposed for randomly creased membranes, is shown to predict with good accuracy the load-displacement relationship of the corners. It uses physically based and hence directly measurable membrane parameters.https://resolver.caltech.edu/CaltechAUTHORS:PAPjsr08Folding Large Antenna Tape Spring
https://resolver.caltech.edu/CaltechAUTHORS:SOYjsr08
Year: 2008
DOI: 10.2514/1.28421
This paper presents a novel concept for a low-mass, 50-m^2-deployable, P-band dual polarization antenna that can measure terrestrial biomass levels from a spacecraft in a low Earth orbit. A monolithic array of feed and radiating patches is bonded to a transversally curved structure consisting of two Kevlar sheets. The first sheet supports the array and the other sheet supports a ground plane. The two sheets are connected by a compliant Kevlar core that allows the whole structure to be folded elastically and to spring back to its original, undamaged shape. Test pieces have been made to demonstrate both the radio frequency and mechanical aspects of the design, particularly the radio frequency performance before and after folding the structure. It is concluded that the proposed design concept has high potential for large, low-frequency antennas for low-cost missions.https://resolver.caltech.edu/CaltechAUTHORS:SOYjsr08Compliant multistable structural elements
https://resolver.caltech.edu/CaltechAUTHORS:SANijss08
Year: 2008
DOI: 10.1016/j.ijsolstr.2008.07.014
Compliant multistable structures are presented which exhibit a large geometric change when actuated between their stable states. It is demonstrated how asymmetric-bistability is achieved through the combination of linear and nonlinear springs. Finite element analytical techniques are provided which enable the design of such structures, and which illustrate how the presence of imperfections can substantially alter their structural performance. A multistable structure is developed which consists of four connected bistable tetrahedral units. The validity of the analytical techniques is confirmed through observation of several physical models.https://resolver.caltech.edu/CaltechAUTHORS:SANijss08Topological optimization of compliant adaptive wing structure
https://resolver.caltech.edu/CaltechAUTHORS:20090506-151236424
Year: 2009
DOI: 10.2514/1.36679
Load-path-based topology optimization is used to synthesize a compliant adaptive aircraft wing leading edge, which deforms in a prescribed way when subject to a single point internal actuation. The load-path-based optimization method requires the specification of a parent lattice. Increasing the complexity of this lattice means the number of parameters required for a complete representation of the structure in the topology optimization becomes prohibitive, although it is desirable to enable a full exploration of the design space. A new method based on graph theory and network analysis is proposed, which enables a substantial reduction in the required number of parameters to represent the parent lattice. The results from this load-path-based approach are compared with those obtained from the better-known density-based topology optimization method.https://resolver.caltech.edu/CaltechAUTHORS:20090506-151236424Multi-objective optimization of free-form grid structures
https://resolver.caltech.edu/CaltechAUTHORS:20091216-121728405
Year: 2010
DOI: 10.1007/s00158-009-0358-4
Computational modeling software facilitates the creation of any surface geometry imaginable, but it is not always obvious how to create an efficient grid shell structure on a complex surface. This paper presents a design tool for synthesis of optimal grid structures, using a Multi-Objective Genetic Algorithm to vary rod directions over the surface in response to two or more load cases. A process of grid homogenization allows the tool to be rapidly applied to any grid structure consisting of a repeating unit cell, including quadrilateral, triangular and double layer grids. Two case studies are presented to illustrate the successful execution of the optimization procedure.https://resolver.caltech.edu/CaltechAUTHORS:20091216-121728405Maximally stable lobed balloons
https://resolver.caltech.edu/CaltechAUTHORS:20100607-120558442
Year: 2010
DOI: 10.1016/j.ijsolstr.2010.02.013
This paper is concerned with the optimization of the cutting pattern of n-fold symmetric super-pressure balloons made from identical lobes constrained by stiff meridional tendons. It is shown that the critical buckling pressure of such balloons is maximized if the unstressed surface area of the balloon is minimized under a stress constraint. This approach results in fully stressed balloon designs that in some cases have a smaller unstressed surface area than the corresponding axisymmetric surface that is in equilibrium with zero hoop stress. It is shown that, compared to current designs, the buckling pressures can be increased by up to 300% without increasing the maximum stress in the lobe.https://resolver.caltech.edu/CaltechAUTHORS:20100607-120558442A Zero-Stiffness Elastic Shell Structure
https://resolver.caltech.edu/CaltechAUTHORS:20110726-075004792
Year: 2011
DOI: 10.2140/jomms.2011.6.203
A remarkable shell structure is described that, due to a particular combination of geometry and initial stress, has zero stiffness for any finite deformation along a twisting path; the shell is in a neutrally stable state of equilibrium. Initially the shell is straight in a longitudinal direction, but has a constant, nonzero curvature in the transverse direction. If residual stresses are induced in the shell by, for example, plastic deformation, to leave a particular resultant bending moment, then an analytical inextensional model of the shell shows it to have no change in energy along a path of twisted configurations. Real shells become closer to the inextensional idealization as their thickness is decreased; experimental thin-shell models have confirmed the neutrally stable configurations predicted by the inextensional theory. A simple model is described that shows that the resultant bending moment that leads to zero stiffness gives the shell a hidden symmetry, which explains this remarkable property.https://resolver.caltech.edu/CaltechAUTHORS:20110726-075004792Quasi-Static Folding and Deployment of Ultrathin Composite Tape-Spring Hinges
https://resolver.caltech.edu/CaltechAUTHORS:20110322-091936641
Year: 2011
DOI: 10.2514/1.47321
Deployable structures made from ultrathin composite materials can be folded elastically and are able to selfdeploy
by releasing the stored strain energy. This paper presents a detailed study of the folding and deployment of a
tape-spring hinge made from a two-ply plain-weave laminate of carbon-fiber reinforced plastic. Aparticular version
of this hinge was constructed, and its moment-rotation profile during quasi-static deployment was measured. The
present study is the first to incorporate in the simulation an experimentally validated elastic micromechanical model
and to provide quantitative comparisons between the simulations and the measured behavior of an actual hinge.
Folding and deployment simulations of the tape-spring hinge were carried out with the commercial finite element
package Abaqus/Explicit, starting from the as-built unstrained structure. The folding simulation includes the effects
of pinching the hinge in the middle to reduce the peak moment required to fold it. The deployment simulation fully
captures both the steady-state moment part of the deployment and the final snap back to the deployed configuration.
An alternative simulation without pinching the hinge provides an estimate of the maximum moment that could be
carried by the hinge during operation. This is about double the snapback moment.https://resolver.caltech.edu/CaltechAUTHORS:20110322-091936641Concept and Design of a Multistable Plate Structure
https://resolver.caltech.edu/CaltechAUTHORS:20110921-112358749
Year: 2011
DOI: 10.1115/1.4004459
A concept is presented for a compliant plate structure that deforms elastically into a variety
of cylindrical shapes and is able to maintain such shapes due to the presence of bistable
components within the structure. The whole structure may be fabricated as a
monolithic entity using low-cost manufacturing techniques such as injection molding.
The key steps in the analysis of this novel concept are presented, and a functional model
is designed and constructed to demonstrate the concept and validate the analysis.https://resolver.caltech.edu/CaltechAUTHORS:20110921-112358749Constitutive modeling of fiber composites with a soft hyperelastic matrix
https://resolver.caltech.edu/CaltechAUTHORS:20120321-092722311
Year: 2012
DOI: 10.1016/j.ijsolstr.2011.11.006
This paper presents an experimental and numerical study of unidirectional carbon fiber composites with a silicone matrix, loaded transversally to the fibers. The experiments show nonlinear behavior with significant strain softening under cyclic loading. The numerical study uses a plane-strain finite element continuum model of the composite material in which the fiber distribution is based on experimental observations and cohesive elements allow debonding to take place at the fiber/matrix interfaces. It is found that accurate estimates of the initial tangent stiffness measured in the experiments can be obtained without allowing for debonding, but this feature has to be included to capture the non-linear and strain-softening behavior.https://resolver.caltech.edu/CaltechAUTHORS:20120321-092722311Folding of fiber composites with a hyperelastic matrix
https://resolver.caltech.edu/CaltechAUTHORS:20120321-093716989
Year: 2012
DOI: 10.1016/j.ijsolstr.2011.09.010
This paper presents an experimental and numerical study of the folding behavior of thin composite materials consisting of carbon fibers embedded in a silicone matrix. The soft matrix allows the fibers to microbuckle without breaking and this acts as a stress relief mechanism during folding, which allows the material to reach very high curvatures. The experiments show a highly non-linear moment vs. curvature relationship, as well as strain softening under cyclic loading. A finite element model has been created to study the micromechanics of the problem. The fibers are modeled as linear-elastic solid elements distributed in a hyperelastic matrix according to a random arrangement based on experimental observations. The simulations obtained from this model capture the detailed micromechanics of the problem and the experimentally observed non-linear response. The proposed model is in good quantitative agreement with the experimental results for the case of lower fiber volume fractions but in the case of higher volume fractions the predicted response is overly stiff.https://resolver.caltech.edu/CaltechAUTHORS:20120321-093716989Thin-Shell Deployable Reflectors with Collapsible Stiffeners: Experiments and Simulations
https://resolver.caltech.edu/CaltechAUTHORS:20120416-095858746
Year: 2012
DOI: 10.2514/1.J051254
This paper presents an experimental and computational study of four deployable reflectors with collapsible edge
stiffeners, to verify the differences in behavior that had been predicted in a previous theoretical study. The
experimental models have different geometric configurations and are made of two different plastics. Both folding
experiments and vibration tests in the fully deployed configuration are carried out on each model, and it is shown that
good correlation with finite element simulations can be achieved if detailed effects such as material nonlinearity,
geometric imperfections, air, and gravity effects are included in the computer models.https://resolver.caltech.edu/CaltechAUTHORS:20120416-095858746Wrinkling of Orthotropic Viscoelastic Membranes
https://resolver.caltech.edu/CaltechAUTHORS:20120402-094931274
Year: 2012
DOI: 10.2514/1.J051255
This paper presents a simplified simulation technique for orthotropic viscoelastic membranes. Wrinkling is
detected by a combined stress–strain criterion and iterative scheme searches for the wrinkle angle using a
pseudoelastic material stiffness matrix based on a nonlinear viscoelastic constitutive model. This simplified model has
been implemented in ABAQUS/Explicit and is able to compute the behavior of a membrane structure by
superposition of a small number of response increments. The model has been tested against a published solution for a
time-independent isotropic membrane under simple shear and against experimental results on Stratofilm 420 under
simple shear.https://resolver.caltech.edu/CaltechAUTHORS:20120402-094931274Satellite Hardware: Stow-and-Go for Space Travel
https://resolver.caltech.edu/CaltechAUTHORS:20120604-143122907
Year: 2012
Man-made satellites have to fit a lot into a compact package. Protected inside a rocket while blasted through the atmosphere, a satellite is launched into Earth orbit, or beyond, to continue its unmanned mission alone. It uses gyroscopes, altitude thrusters, and magnets to regulate sun exposure and stay pointed in the right direction. Once stable, the satellite depends on solar panels to recharge its internal batteries, mirrors, and lenses for data capture, and antennas for communication back to Earth. Whether it is a bread-loaf-sized nano, or the school bus sized Hubble Telescope, every satellite is susceptible to static electricity buildup from solar wind, the very cold temperatures the Earth's shadow (or deep space), and tiny asteroids along the route.https://resolver.caltech.edu/CaltechAUTHORS:20120604-143122907Space-quality data from balloon-borne telescopes: the High Altitude Lensing Observatory (HALO)
https://resolver.caltech.edu/CaltechAUTHORS:20121212-100123634
Year: 2012
DOI: 10.1016/j.astropartphys.2012.05.015
We present a method for attaining sub-arcsecond pointing stability during sub-orbital balloon flights, as
designed for in the High Altitude Lensing Observatory (HALO) concept. The pointing method presented here
has the potential to perform near-space quality optical astronomical imaging at ~1–2% of the cost of
space-based missions. We also discuss an architecture that can achieve sufficient thermo-mechanical stability
to match the pointing stability. This concept is motivated by advances in the development and testing
of Ultra Long Duration Balloon (ULDB) flights which promise to allow observation campaigns lasting
more than three months. The design incorporates a multi-stage pointing architecture comprising: a gondola
coarse azimuth control system, a multi-axis nested gimbal frame structure with arcsecond stability,
a telescope de-rotator to eliminate field rotation, and a fine guidance stage consisting of both a telescope
mounted angular rate sensor and guide CCDs in the focal plane to drive a Fast-Steering Mirror. We discuss
the results of pointing tests together with a preliminary thermo-mechanical analysis required for subarcsecond
pointing at high altitude. Possible future applications in the areas of wide-field surveys and
exoplanet searches are also discussed.https://resolver.caltech.edu/CaltechAUTHORS:20121212-100123634Failure of Carbon Fibers at a Crease in a Fiber-Reinforced Silicone Sheet
https://resolver.caltech.edu/CaltechAUTHORS:20130204-114025514
Year: 2013
DOI: 10.1115/1.4007082
Thin sheets of unidirectional carbon fibers embedded in a silicone matrix can be folded to very high curvatures, as elastic microbuckles with a half-wavelength on the order of 1 mm decrease the maximum strain in the fibers near the compression surface. This paper shows that probabilistic failure models derived from tension tests on individual fibers can be used to predict accurately the value of the outer surface curvature of the sheet, at which a small percentage of fibers break when a crease is formed in the sheet. The most accurate results are obtained by using a strain-based Weibull distribution of the failure probability in tension.https://resolver.caltech.edu/CaltechAUTHORS:20130204-114025514Failure criterion for two-ply plain-weave CFRP laminates
https://resolver.caltech.edu/CaltechAUTHORS:20130625-091951266
Year: 2013
DOI: 10.1177/0021998312447208
We present an experimentally based failure criterion for symmetric two-ply plain-weave laminates of carbon fiber reinforced plastic. The criterion is formulated in terms of six force and moment stress resultants and consists of a set of three inequalities, related to in-plane, bending, and combined in-plane and bending types of failure. All failure parameters in the criterion are measured directly from five sets of tests. The new criterion is validated against an extensive data set of failure test results that use novel sample configurations to impose different combinations of stress resultants. It is found that the proposed criterion is safe for all test conditions and yet avoids excessive conservatism.https://resolver.caltech.edu/CaltechAUTHORS:20130625-091951266Folding, Stowage, and Deployment of Viscoelastic Tape Springs
https://resolver.caltech.edu/CaltechAUTHORS:20130829-140823015
Year: 2013
DOI: 10.2514/1.J052269
This paper presents an experimental and numerical study of the folding, stowage, and deployment behavior of
viscoelastic tape springs. Experiments show that during folding the relationship between load and displacement is
nonlinear and varies with rate and temperature. In particular, the limit and propagation loads increase with the
folding rate but decrease with temperature. During stowage, relaxation behavior leads to a reduction in internal
forces that significantly impacts the subsequent deployment dynamics. The deployment behavior starts with a short,
dynamic transient that is followed by a steady deployment and ends with a slow creep recovery. Unlike elastic tape
springs, localized folds in viscoelastic tape springs do not move during deployment. Finite-element simulations based
on a linear viscoelastic constitutive model with an experimentally determined relaxation modulus are shown to
accurately reproduce the experimentally observed behavior, and to capture the effects of geometric nonlinearity, time
and temperature dependence.https://resolver.caltech.edu/CaltechAUTHORS:20130829-140823015Ultralightweight deformable mirrors
https://resolver.caltech.edu/CaltechAUTHORS:20130822-142341866
Year: 2013
DOI: 10.1364/AO.52.005327
This paper presents a concept for ultralightweight deformable mirrors, based on a thin substrate of optical surface quality, coated with continuous active layers that provide separate modes of actuation at different length scales. This concept eliminates any kind of stiff backing structure for the mirror surface and exploits microfabrication technologies to provide tight integration of the active materials into the mirror structure, to avoid actuator print-through effects. Proof-of-concept, 10 cm diameter mirrors with an areal density of 0.6 kg/m^2 have been designed, built, and tested to measure their shape-correction performance and verify the finite-element models used for design. The low-cost manufacturing scheme involves low-temperature processing steps (below 140°C) to minimize residual stresses, does not require precision photolithography, and is therefore scalable to larger diameters depending on application requirements.https://resolver.caltech.edu/CaltechAUTHORS:20130822-142341866Trajectory Planning for CubeSat Short-Time-Scale Proximity Operations
https://resolver.caltech.edu/CaltechAUTHORS:20140626-094453645
Year: 2014
DOI: 10.2514/1.60289
This paper considers motion planning for small satellites such as CubeSats performing proximity operations in a several meters range of a target object. The main goal is to develop a principled methodology for handling the coupled effects of orbital dynamics, rotational and translational rigid-body dynamics, underactuation and control bounds, and obstacle avoidance constraints. The proposed approach is based on constructing a reduced-order parameterization of the dynamics through dynamics inversion and differential flatness, and on efficient global optimization over a finite-dimensional reduced representation. Two simulated scenarios, a satellite reconfiguration maneuver and asteroid surface sampling, are developed to illustrate the approach. In addition, a simple two-dimensional experimental testbed consisting of an air-bearing table and two CubeSat engineering models is developed for partial testing and integration of the proposed methods.https://resolver.caltech.edu/CaltechAUTHORS:20140626-094453645Deployment Dynamics of Ultrathin Composite Booms with Tape-Spring Hinges
https://resolver.caltech.edu/CaltechAUTHORS:20140501-090732942
Year: 2014
DOI: 10.2514/1.A32401
An experimental and numerical study of the dynamic deployment of stored strain energy deployable booms with tape-spring hinges made of woven carbon fiber composite is presented. The deployment consists of three phases: deployment, one or more attempts to latch, and a small amplitude vibration. Twelve nominally identical deployment experiments show that the deployment and vibration phases are repeatable, whereas considerable scatter is observed during latching. A high-fidelity finite element shell model of the complete boom is used to carry out complete dynamic simulations with the Abaqus/Explicit finite element software. These analyses provide detailed time histories of deformation and stress distribution. By varying the end conditions at the root of the boom and the viscous pressure loading on the surface of the hinge region, the analyses provide 1) an envelope of responses that bound the complete set of experimental observations and 2) responses that closely approximate actual experiments. The presented approach is fully general and can provide high-fidelity simulations for any kind of stored-energy deployable structure.https://resolver.caltech.edu/CaltechAUTHORS:20140501-090732942Manufacture of Arbitrary Cross-Section Composite Honeycomb Cores Based on Origami Techniques
https://resolver.caltech.edu/CaltechAUTHORS:20140509-130505268
Year: 2014
DOI: 10.1115/1.4026824
As observed in the design of antenna reflectors and rocket bodies, both flat and 3D-shaped honeycomb cores are used in the field of aerospace engineering. This study illustrates
a new strategy to fabricate arbitrary cross-section honeycombs with applications of advanced composite materials by using the concept of the kirigami honeycomb, which is made from single flat sheets and has periodical slits resembling origami. The authors also describe a method of applying this technique to advanced composite materials.
Applying the partially soft composite techniques, 3D shaped composite honeycombs are manufactured, and some typical samples are shown with their folding line diagrams.https://resolver.caltech.edu/CaltechAUTHORS:20140509-130505268Design of Ultrathin Composite Self-Deployable Booms
https://resolver.caltech.edu/CaltechAUTHORS:20150105-090948670
Year: 2014
DOI: 10.2514/1.A32815
Recently developed analysis techniques for thin shells that can be folded elastically and are able to self-deploy are used to develop an iterative design approach for this type of structure. The proposed approach considers a series of potential designs and then evaluates, for each trial design, key performance parameters through a complete simulation of its folding and deployment behavior. This design approach is applied to a boom concept consisting of a thin-walled tube in which two tape-spring hinges are made by cutting diametrically opposite slots; the geometry of the slots is fully defined by the length, width, and end diameter of the cuts. A design for a two-hinge, 1-m-long, lightweight self-deployable boom that can be wrapped around a small spacecraft is developed; the hinge geometry is chosen such that there is no damage during folding/deployment of the boom, and also the boom becomes latched at the first attempt. The chosen boom design is successfully validated experimentally.https://resolver.caltech.edu/CaltechAUTHORS:20150105-090948670Design algorithm for the placement of identical segments in a large spherical mirror
https://resolver.caltech.edu/CaltechAUTHORS:20150402-133733867
Year: 2015
DOI: 10.1117/1.JATIS.1.2.024002
We present a design algorithm to compute the positions of identical, hexagonal mirror segments on a spherical surface, which is shown to provide a small variation in gap width. A one-dimensional analog to the segmentation problem is developed in order to motivate the desired configuration of the tiling patterns and to emphasize the desire for minimizing segment gap widths to improve optical performance. Our azimuthal equidistant centroid tiling algorithm is applied to three telescope architectures and produces mirror segment arrangements that compare favorably with existing and alternative designs.https://resolver.caltech.edu/CaltechAUTHORS:20150402-133733867Viscoplastic tearing of polyethylene thin film
https://resolver.caltech.edu/CaltechAUTHORS:20150706-104549692
Year: 2015
DOI: 10.1007/s11043-015-9259-7
Recent advances in noncontact strain measurement techniques and large-strain constitutive modeling of the linear low-density polyethylene film used in NASA superpressure balloons StratoFilm 420 are combined to provide a novel measurement technique for the tear propagation critical value of the J-integral. Previously these measurements required complex test configurations and procedures. It is found that the critical value of the J-integral increases by approximately 50 % when the strain rate is decreased from 1.33×10^−4 s^−1 to 1.33×10^−5 s^−1. It is shown that there is good correlation between measurements made on uniaxially loaded dogbone samples and circular diaphragms loaded by pressure, both with a 2-mm-wide slit in the middle. This result indicates that more extensive studies of strain-rate dependence may be made with the simpler, uniaxial test configuration.https://resolver.caltech.edu/CaltechAUTHORS:20150706-104549692Optimized actuators for ultrathin deformable primary mirrors
https://resolver.caltech.edu/CaltechAUTHORS:20150520-080116235
Year: 2015
DOI: 10.1364/AO.54.004937
A novel design and selection scheme for surface-parallel actuators for ultrathin, lightweight mirrors is presented. The actuation system consists of electrodes printed on a continuous layer of piezoelectric material bonded to an optical-quality substrate. The electrodes provide almost full coverage of the piezoelectric layer, in order to maximize the amount of active material that is available for actuation, and their shape is optimized to maximize the correctability and stroke of the mirror for a chosen number of independent actuators and for a dominant imperfection mode. The starting point for the design of the electrodes is the observation that the correction of a figure error that has at least two planes of mirror symmetry is optimally done with twin actuators that have the same optimized shape but are rotated through a suitable angle. Additional sets of optimized twin actuators are defined by considering the intersection between the twin actuators, and hence an arbitrarily fine actuation pattern can be generated. It is shown that this approach leads to actuator systems with better performance than simple, geometrically based actuators. Several actuator patterns to correct third-order astigmatism aberrations are presented, and an experimental demonstration of a 41-actuator mirror is also presented.https://resolver.caltech.edu/CaltechAUTHORS:20150520-080116235Imperfection-insensitive axially loaded thin cylindrical shells
https://resolver.caltech.edu/CaltechAUTHORS:20150604-080335187
Year: 2015
DOI: 10.1016/j.ijsolstr.2014.12.030
The high efficiency of circular monocoque cylindrical shells in carrying axial loads is impaired by their extreme sensitivity to imperfections and there is an extensive body of literature that addresses this behavior. Instead of following this classical path, focused on circular cross-sections, this paper presents a novel approach that adopts optimal symmetry-breaking wavy cross-sections (wavy shells). The avoidance of imperfection sensitivity is achieved by searching with an evolutionary algorithm for smooth cross-sectional shapes that maximize the minimum among the buckling loads of geometrically perfect and imperfect wavy shells. It is found that shells designed through this approach can achieve higher critical stresses and knockdown factors than any previously known monocoque cylindrical shells. It is also found that these shells have superior mass efficiency to almost all previously reported stiffened shells.https://resolver.caltech.edu/CaltechAUTHORS:20150604-080335187Using CubeSat/micro-satellite technology to demonstrate the Autonomous Assembly of a Reconfigurable Space Telescope (AAReST)
https://resolver.caltech.edu/CaltechAUTHORS:20150806-141005388
Year: 2015
DOI: 10.1016/j.actaastro.2015.04.008
Future space telescopes with diameter over 20 m will require new approaches: either high-precision formation flying or in-orbit assembly. We believe the latter holds promise at a potentially lower cost and more practical solution in the near term, provided much of the assembly can be carried out autonomously. To gain experience, and to provide risk reduction, we propose a combined micro/nano-satellite demonstration mission that will focus on the required optical technology (adaptive mirrors, phase-sensitive detectors) and autonomous rendezvous and docking technology (inter-satellite links, relative position sensing, automated docking mechanisms). The mission will involve two "3U" CubeSat-like nanosatellites ("MirrorSats") each carrying an electrically actuated adaptive mirror, and each capable of autonomous un-docking and re-docking with a small central "15U" class micro/nano-satellite core, which houses two fixed mirrors and a boom-deployed focal plane assembly. All three spacecrafts will be launched as a single ~40 kg micro-satellite package. The spacecraft busses are based on heritage from Surrey׳s SNAP-1 and STRaND-1 missions (launched in 2000 and 2013 respectively), whilst the optics, imaging sensors and shape adjusting adaptive mirrors (with their associated adjustment mechanisms) are provided by CalTech/JPL. The spacecraft busses provide precise orbit and attitude control, with inter-satellite links and optical navigation to mediate the docking process. The docking system itself is based on the electromagnetic docking system being developed at the Surrey Space Centre (SSC), together with rendezvous sensing technology developed for STRaND-2. On orbit, the mission profile will firstly establish the imaging capability of the compound spacecraft before undocking, and then autonomously re-docking a single MirrorSat. This will test the docking system, autonomous navigation and system identification technology. If successful, the next stage will see the two MirrorSat spacecraft undock and re-dock to the core spacecraft in a linear formation to represent a large (but sparse) aperture for high resolution imaging. The imaging of stars is the primary objective, but other celestial and terrestrial targets are being considered. Teams at CalTech and SSC are currently working on the mission planning and development of space hardware. The autonomous rendezvous and docking system is currently under test on a 2D air-bearing table at SSC, and the propulsion and precision attitude control system is currently in development. Launch is planned for 2016. This paper details the mission concept; technology involved and progress to date, focussing on the spacecraft buses.https://resolver.caltech.edu/CaltechAUTHORS:20150806-141005388Effects of Long-Term Stowage on the Deployment of Bistable Tape Springs
https://resolver.caltech.edu/CaltechAUTHORS:20160408-093030473
Year: 2016
DOI: 10.1115/1.4031618
In the context of strain-energy-deployed space structures, material relaxation effects play a significant role in structures that are stowed for long durations, for example, in a space vehicle prior to launch. Here, the deployment of an ultrathin carbon fiber reinforced plastic (CFRP) tape spring is studied, with the aim of understanding how long-duration stowage affects its deployment behavior. Analytical modeling and experiments show that the deployment time increases predictably with stowage time and temperature, and analytical predictions are found to compare well with experiments. For cases where stress relaxation is excessive, the structure is shown to lose its ability to deploy autonomously.https://resolver.caltech.edu/CaltechAUTHORS:20160408-093030473Thermoviscoelastic models for polyethylene thin films
https://resolver.caltech.edu/CaltechAUTHORS:20151116-102001293
Year: 2016
DOI: 10.1007/s11043-015-9282-8
This paper presents a constitutive thermoviscoelastic model for thin films of linear low-density polyethylene subject to strains up to yielding. The model is based on the free volume theory of nonlinear thermoviscoelasticity, extended to orthotropic membranes. An ingredient of the present approach is that the experimentally inaccessible out-of-plane material properties are determined by fitting the model predictions to the measured nonlinear behavior of the film. Creep tests, uniaxial tension tests, and biaxial bubble tests are used to determine the material parameters. The model has been validated experimentally, against data obtained from uniaxial tension tests and biaxial cylindrical tests at a wide range of temperatures and strain rates spanning two orders of magnitude.https://resolver.caltech.edu/CaltechAUTHORS:20151116-102001293UHF Deployable Helical Antennas for CubeSats
https://resolver.caltech.edu/CaltechAUTHORS:20160913-085506285
Year: 2016
DOI: 10.1109/TAP.2016.2583058
The design process and the deployment mechanism of a quadrifilar helix antenna (QHA) and a conical log spiral antenna (CLSA) are presented. The two antennas are proposed to operate in the UHF frequency band. They are composed of conductors that are embedded and supported by innovative structural techniques. This allows efficient folding, packaging, and deployment once in space. The conductors in the QHA are composed of beryllium copper and are supported by helical arms of S_2 glass fiber reinforced epoxy. The CLSA, on the other hand, has conductors that are made out of a mesh of phosphor bronze and incorporated inside thin insulators composed of continuous fiber composites. The new aspects of these designs lie in their structures and deployment mechanisms. The deployment mechanisms for both antennas include helical pantograph and origami patterns such as Z-folding configurations. Both antennas are fabricated and tested for both deployment and radiation performance. A comparison is executed between both designs, and their potential deployment possibilities from CubeSats are also investigated.https://resolver.caltech.edu/CaltechAUTHORS:20160913-085506285Architecture for in-space robotic assembly of a modular space telescope
https://resolver.caltech.edu/CaltechAUTHORS:20160713-105905208
Year: 2016
DOI: 10.1117/1.JATIS.2.4.041207
An architecture and conceptual design for a robotically assembled, modular space telescope (RAMST) that enables extremely large space telescopes to be conceived is presented. The distinguishing features of the RAMST architecture compared with prior concepts include the use of a modular deployable structure, a general-purpose robot, and advanced metrology, with the option of formation flying. To demonstrate the feasibility of the robotic assembly concept, we present a reference design using the RAMST architecture for a formation flying 100-m telescope that is assembled in Earth orbit and operated at the Sun–Earth Lagrange Point 2.https://resolver.caltech.edu/CaltechAUTHORS:20160713-105905208Nonlinear dynamic analysis of creased shells
https://resolver.caltech.edu/CaltechAUTHORS:20161111-101434125
Year: 2016
DOI: 10.1016/j.finel.2016.07.008
Recent studies analyze the behavior of advanced shell structures, like foldable, multistable or morphing shell structures. Simulating a thin foldable curved structure is not a trivial task: the structure may go through many snapping transitions from a stable configuration to another. Then, one could claim arc-length methods or use a dynamic approach to perform such simulations. This work presents a geometrically exact shell model for nonlinear dynamic analysis of shells. An updated Lagrangian framework is used for describing kinematics. Several numerical examples of folding a thin dome are presented, including creased shells. The triangular shell finite element used offers great flexibility for the generation of the unstructured curved meshes, as well as great results.https://resolver.caltech.edu/CaltechAUTHORS:20161111-101434125Bloch wave buckling analysis of axially loaded periodic cylindrical shells
https://resolver.caltech.edu/CaltechAUTHORS:20161202-074257153
Year: 2016
DOI: 10.1016/j.compstruc.2016.09.006
This paper presents an efficient computational method for predicting the onset of buckling of axially loaded, corrugated or stiffened cylindrical shells. This method is a modification of the Bloch wave method which builds on the stiffness matrix method. A numerical method and an efficient algorithm have been developed to implement the proposed method in the commercial finite element package Abaqus. Numerical examples have shown that, compared to the nonlinear buckling analyses based on detailed full finite element models, the proposed method can obtain highly accurate buckling loads and buckling modes and can achieve very significant reductions in computational time.https://resolver.caltech.edu/CaltechAUTHORS:20161202-074257153Micromechanics Models for Viscoelastic Plain-Weave Composite Tape Springs
https://resolver.caltech.edu/CaltechAUTHORS:20170216-123337810
Year: 2017
DOI: 10.2514/1.J055041
The viscoelastic behavior of polymer composites decreases the deployment force and the postdeployment shape accuracy of composite deployable space structures. This paper presents a viscoelastic model for single-ply cylindrical shells (tape springs) that are deployed after being held folded for a given period of time. The model is derived from a representative unit cell of the composite material, based on the microstructure geometry. Key ingredients are the fiber volume density in the composite tows and the constitutive behavior of the fibers (assumed to be linear elastic and transversely isotropic) and of the matrix (assumed to be linear viscoelastic). Finite-element-based homogenizations at two scales are conducted to obtain the Prony series that characterize the orthotropic behavior of the composite tow, using the measured relaxation modulus of the matrix as an input. A further homogenization leads to the lamina relaxation ABDABD matrix. The accuracy of the proposed model is verified against the experimentally measured time-dependent compliance of single lamina in either pure tension or pure bending. Finite element simulations of single-ply tape springs based on the proposed model are compared to experimental measurements that were also obtained during this study.https://resolver.caltech.edu/CaltechAUTHORS:20170216-123337810Crease-free biaxial packaging of thick membranes with slipping folds
https://resolver.caltech.edu/CaltechAUTHORS:20170407-080803700
Year: 2017
DOI: 10.1016/j.ijsolstr.2016.08.013
This paper presents a novel scheme to biaxially package and deploy flat membranes, in which the thickness of the membrane is accounted for through the novel concept of slipping folds. The membrane is divided into parallel strips connected by slipping folds, and specially chosen wrapping profiles that require zero slip along the edges of the membrane are identified. This packaging scheme avoids the kinematic incompatibilities that in other schemes result in local buckles and wrinkles that increase the deployment force and permanently deform the membrane. The paper also presents a scheme to apply uniform uniaxial prestress to the deployed membrane, as well as a two-stage deployment scheme. Packaging efficiencies of up to 83% have been demonstrated for meter-scale models, although for large membranes the packaging efficiency approaches 100%.https://resolver.caltech.edu/CaltechAUTHORS:20170407-080803700Post-cure shape errors of ultra-thin symmetric CFRP laminates: Effect of ply-level imperfections
https://resolver.caltech.edu/CaltechAUTHORS:20170317-082612485
Year: 2017
DOI: 10.1016/j.compstruct.2016.12.075
This paper discusses the effect of misalignments in ply orientation, uniform variations in ply thickness, and through-thickness thermal gradients on the post-cure shape errors for symmetric cross-ply laminates constructed from ultra-thin composite materials. Photogrammetry-based surface measurements are performed for laminates cured at elevated temperatures. Significant out-of-plane shape errors are observed, with amplitudes ∼75 times the laminate thickness. The magnitude of each imperfection is also characterized experimentally on coupon-level samples. A non-linear finite element model is developed and demonstrates that these imperfections result in cylindrical and twisting modes of deformation. Results are compared to Classical Lamination Theory predictions which are shown to be inadequate in predicting shape errors that require changes in Gaussian curvature. Through these studies, it is determined that thickness variations between the top and bottom plies have the most pronounced effect on shape errors.https://resolver.caltech.edu/CaltechAUTHORS:20170317-082612485Rapid Design of Deployable Antennas for CubeSats: A tool to help designers compare and select antenna topologies
https://resolver.caltech.edu/CaltechAUTHORS:20170303-105701054
Year: 2017
DOI: 10.1109/MAP.2017.2655531
A novel methodology for the rapid preliminary design of
deployable antennas for CubeSats is proposed in this
article. It uses a graphical representation of antenna
performance, consisting of a set of plots of different
performance metrics against antenna geometry parameters.
Coupled electromagnetic and structural design problems are
addressed easily, enabling the rapid and direct comparison of different antenna concepts. This approach is demonstrated
for a case study at ultrahigh frequency (UHF), comparing
the performance of a dipole, a helix, a conical horn, and a
conical log spiral (CLS), all based on dual-matrix composite
deployable structures. The initial design space of antenna
geometries is reduced by two orders of magnitude to a set
of constraint-satisfying designs. A graphical user interface
implementing the approach is presented, and the accuracy of
the method is briefly addressed.https://resolver.caltech.edu/CaltechAUTHORS:20170303-105701054Experiments on imperfection insensitive axially loaded cylindrical shells
https://resolver.caltech.edu/CaltechAUTHORS:20170526-080151216
Year: 2017
DOI: 10.1016/j.ijsolstr.2017.02.028
This paper presents an experimental study of imperfection insensitive composite wavy cylindrical shells subject to axial compression. A fabrication technique for making cylindrical shells with intricate shape of cross-sections has been developed. A photogrammetry technique to measure the geometric imperfections has also been developed. The behavior of the wavy shells under axial compression was predicted through simulations and measured through compression tests. Both the analyses and experiments have confirmed that the wavy shells are imperfection insensitive. Comparisons between the wavy shells and circular shells have also confirmed that introducing optimal symmetry-breaking wavy cross-sections can significantly reduce the imperfection sensitivity and improve the load-bearing capability of cylindrical shells.https://resolver.caltech.edu/CaltechAUTHORS:20170526-080151216Molecular based temperature and strain rate dependent yield criterion for anisotropic elastomeric thin films
https://resolver.caltech.edu/CaltechAUTHORS:20170818-092431386
Year: 2017
DOI: 10.1016/j.polymer.2017.07.080
A molecular formulation of the onset of plasticity is proposed to assess temperature and strain rate effects in anisotropic semi-crystalline rubbery films. The presented plane stress criterion is based on the strain rate-temperature superposition principle and the cooperative theory of yielding, where some parameters are assumed to be material constants, while others are considered to depend on specific modes of deformation. An orthotropic yield function is developed for a linear low density polyethylene thin film. Uniaxial and biaxial inflation experiments were carried out to determine the yield stress of the membrane via a strain recovery method. It is shown that the 3% offset method predicts the uniaxial elastoplastic transition with good accuracy. Both the tensile yield points along the two principal directions of the film and the biaxial yield stresses are found to obey the superposition principle. The proposed yield criterion is compared against experimental measurements, showing excellent agreement over a wide range of deformation rates and temperatures.https://resolver.caltech.edu/CaltechAUTHORS:20170818-092431386Nonlinear thermomechanical response and constitutive modeling of viscoelastic polyethylene membranes
https://resolver.caltech.edu/CaltechAUTHORS:20171018-094843923
Year: 2018
DOI: 10.1016/j.mechmat.2017.10.004
Thin films of linear low-density polyethylene show a significant time-dependent behavior, strongly reliant on temperature and strain rate effects. A constitutive nonlinear thermo-viscoelastic relation is developed to characterize the response of thin membranes up to yielding, in a wide range of temperatures, strain rates, and mechanical loading conditions. The presented plane stress orthotropic formulation involves the free volume theory of viscoelasticity and the time-temperature superposition principle, necessary to describe non-linearities and non-isothermal conditions. Uniaxial tension tests at constant strain rate and long-duration biaxial inflation experiments have been employed in the calibration of the material parameters. The model has been implemented in the Abaqus finite element code by means of a user-defined subroutine based on a recursive integration algorithm. The accuracy of the constitutive relation has been validated against experimental data of full field diaphragm inflation tests and uniaxial tension, relaxation and cyclic experiments, covering sub-ambient temperatures and strain rate ranges observed during the operation of stratospheric balloons.https://resolver.caltech.edu/CaltechAUTHORS:20171018-094843923Wrinkling of Transversely Loaded Spinning Membranes
https://resolver.caltech.edu/CaltechAUTHORS:20180214-081512136
Year: 2018
DOI: 10.1016/j.ijsolstr.2018.01.031
Spinning membrane structures provide a mass-efficient solution for large space apertures. This paper presents a detailed study of the wrinkling of spinning circular membranes loaded by transverse, uniform loads. Experimental measurements of the angular velocities at which different membranes become wrinkled, and of the wrinkling mode transitions that occur upon spin down of the membrane, are presented. A theoretical formulation of the problem is presented, from which pairs of critical angular velocities and critical transverse loads are determined. A general stability chart is presented, which identifies the stability limits in terms of only two dimensionless parameters, for any membrane. The transition between bending dominated behavior and in-plane dominated behavior is identified, and it is shown that in the bending-dominated case the critical non-dimensional transverse load is independent from the non-dimensional angular velocity.https://resolver.caltech.edu/CaltechAUTHORS:20180214-081512136Design of ultra-thin shell structures in the stochastic post-buckling range using Bayesian machine learning and optimization
https://resolver.caltech.edu/CaltechAUTHORS:20180221-091817099
Year: 2018
DOI: 10.1016/j.ijsolstr.2018.01.035
A data-driven computational framework combining Bayesian regression for imperfection-sensitive quantities of interest, uncertainty quantification and multi-objective optimization is developed for the design of complex structures. The framework is used to design ultra-thin carbon fiber deployable shells subjected to two bending conditions. Significant increases in the ultimate buckling loads are shown to be possible, with potential gains on the order of 100% as compared to a previously proposed design. The key to this result is the existence of a large load reserve capability after the initial bifurcation point and well into the post-buckling range that can be effectively explored by the data-driven approach. The computational strategy here presented is general and can be applied to different problems in structural and materials design, with the potential of finding relevant designs within high-dimensional spaces.https://resolver.caltech.edu/CaltechAUTHORS:20180221-091817099Nonlinear vibration of transversely-loaded spinning membranes
https://resolver.caltech.edu/CaltechAUTHORS:20180502-090136585
Year: 2018
DOI: 10.1016/j.jsv.2018.04.015
The paper studies the transverse nonlinear vibration of an isotropic and homogeneous annular membrane spinning at constant angular velocity, under the action of a uniform transverse load. The equilibrium configuration of the membrane, clamped along the inner edge and free along the outer edge, and the natural frequencies of vibration of the membrane are calculated. A Galerkin procedure is used to determine a reduced order model describing the weakly nonlinear vibration of the membrane, and it is shown that near-resonance vibration can be modeled as a single degree of freedom Helmholtz-Duffing oscillator. A detailed study at vibration frequencies close to the fundamental, axisymmetric vibration mode shows a transition from softening to hardening behavior, and jump phenomena or hysteretic behavior depending on the angular velocity, the transverse load, the amplitude of dynamic excitation and the damping ratio. The results are in agreement with dynamic implicit finite element simulations in Abaqus/Standard and direct experimental measurements.https://resolver.caltech.edu/CaltechAUTHORS:20180502-090136585Searching for Imperfection Insensitive Externally Pressurized Near-Spherical Thin Shells
https://resolver.caltech.edu/CaltechAUTHORS:20180615-091650052
Year: 2018
DOI: 10.1016/j.jmps.2018.06.008
This paper studies the buckling behavior and imperfection sensitivity of geodesic and stellated shells subject to external pressure. It is shown that these structures can completely eliminate the severe imperfection sensitivity of spherical shells and can achieve buckling pressure and mass efficiency higher than the perfect sphere. Key results of this paper are as follows. First, a shell with the shape of an icosahedron can carry external pressure significantly higher than a spherical shell, when the effects of geometric imperfections are considered. Second, stellated shells are generally insensitive to imperfections. For pyramids with height-to-radius ratios greater than 35% the buckling pressure is greater than for a perfect sphere. The specific ratio 45% gives the highest buckling pressure, 28% higher than the perfect sphere. Third, stellated icosahedra with concave pyramids have higher mass efficiency than the perfect sphere. Fourth, in terms of volume efficiency, geodesic shells are comparable to spherical shells with a knockdown factor of 0.2 and convex stellated shells are comparable to spherical shells with a knockdown factor of 0.65.https://resolver.caltech.edu/CaltechAUTHORS:20180615-091650052Closed Cross-Section Dual-Matrix Composite Hinge for Deployable Structures
https://resolver.caltech.edu/CaltechAUTHORS:20181022-154930890
Year: 2019
DOI: 10.1016/j.compstruct.2018.10.040
Dual-matrix composite structures with localized elastomer composite hinges have been proposed to enable packaging with much smaller fold radii than allowed by traditional resin-based fiber reinforced composites. Previous studies have been limited to proof-of-concept of folding capabilities and constitutive modeling of elastomer composites. A novel closed cross-section dual-matrix deployable hinge is studied here to develop the tools for studying the deployment of general dual-matrix structures. A set of tools for the analysis of deployment of this simple structure is developed: an analytic model that minimizes the strain energy in the folded configuration, experimental characterization, and finite element techniques using the LS-Dyna commercial software. The three models are used to predict the packaged shape and deployment moments, and are shown to be in good agreement amongst themselves. The analytic model is used to demonstrate control of the folded shape of the hinge using the stiffness of the elastomer composite. This behavior is verified using finite element models developed in the LS-Dyna commercial code. The simulations are used to predict the localized fold radius of the hinge within 3% and deployment moments within 5% by accounting for the microbuckled stiffness of the elastomer composite.https://resolver.caltech.edu/CaltechAUTHORS:20181022-154930890A flexible phased array system with low areal mass density
https://resolver.caltech.edu/CaltechAUTHORS:20190416-120325923
Year: 2019
DOI: 10.1038/s41928-019-0247-9
Phased arrays are multiple antenna systems capable of forming and steering beams electronically using constructive and destructive interference between sources. They are employed extensively in radar and communication systems but are typically rigid, bulky and heavy, which limits their use in compact or portable devices and systems. Here, we report a scalable phased array system that is both lightweight and flexible. The array architecture consists of a self-monitoring complementary metal–oxide–semiconductor-based integrated circuit, which is responsible for generating multiple independent phase- and amplitude-controlled signal channels, combined with flexible and collapsible radiating structures. The modular platform, which can be collapsed, rolled and folded, is capable of operating standalone or as a subarray in a larger-scale flexible phased array system. To illustrate the capabilities of the approach, we created a 4 × 4 flexible phased array tile operating at 9.4–10.4 GHz, with a low areal mass density of 0.1 g cm^(−2). We also created a flexible phased array prototype that is powered by photovoltaic cells and intended for use in a wireless space-based solar power transfer array.https://resolver.caltech.edu/CaltechAUTHORS:20190416-120325923Shear-induced buckling of a thin elastic disk undergoing spin-up
https://resolver.caltech.edu/CaltechAUTHORS:20190208-125359102
Year: 2019
DOI: 10.1016/j.ijsolstr.2019.01.038
The stability of a spinning thin elastic disk has been widely studied due to its central importance in engineering. While the plastic deformation and failure of an annular disk mounted on a rigid and accelerating circular shaft are well understood, shear-induced elastic buckling of the disk due to this 'spin-up' is yet to be reported. Here, we calculate this buckling behavior within the framework of the Föppl–von Kármán equations and give numerical results as a function of the disk's aspect ratio (inner-to-outer radius) and Poisson's ratio. This shows that shear-induced elastic buckling can dominate plastic failure in many cases of practical interest. When combined with existing theory for plastic failure, the results of the present study provide foundation results for a multitude of applications including the characterization of accelerating compact disks and deployment of space sails by centrifugal forces.https://resolver.caltech.edu/CaltechAUTHORS:20190208-125359102A Theory for the Design of Multi-Stable Morphing Structures
https://resolver.caltech.edu/CaltechAUTHORS:20191025-133026102
Year: 2020
DOI: 10.1016/j.jmps.2019.103772
Multi-stable structures can provide desired reconfigurability and require relatively simple actuation. This paper considers general bar and plate structures connected by frictionless hinges that are to be made locally stable in a set of chosen target configurations by attaching extensional and rotational, linear-elastic springs to the structure. The unstressed lengths and angles of the springs, as well as their stiffnesses, are the unknown design parameters to be determined. A set of equilibrium and stability conditions to be satisfied in each of the target configurations of the structure are derived. Solutions of these equations provide specific values of the spring properties that correspond to local energy minima in all of the target configurations. The formulation is fully general and is applicable to structures of any complexity. A simple example is used to illustrate the design process for a bi-stable origami structure and a physical prototype is also presented.https://resolver.caltech.edu/CaltechAUTHORS:20191025-133026102Power-Optimal Guidance for Planar Space Solar Power Satellites
https://resolver.caltech.edu/CaltechAUTHORS:20191224-093207317
Year: 2020
DOI: 10.2514/1.g004643
This paper presents power-optimal guidance for a planar space solar power satellite (SSPS). Power-optimal guidance is the attitude trajectory that maximizes the solar power transmitted by the SSPS. Planarity is important because it couples the orientations of the SSPS's photovoltaic and antenna surfaces. Hence, the transmitted power depends on the relative geometry between the SSPS, the sun, and the receiving station. The orientation that maximizes power transfer changes as this relative geometry changes. Both single- and dual-sided SSPS architectures are considered. A single-sided SSPS has one photovoltaic surface and one antenna surface. A dual-sided SSPS is a single-sided SSPS with at least one additional photovoltaic or antenna surface. Geometric arguments show that a dual-sided SSPS has superior performance to a single-sided SSPS. Power-optimal guidance is then presented for the special cases of SSPSs in geostationary Earth orbit, medium Earth orbit, and low Earth orbit transmitting to an equatorial receiving station at the time of Earth's vernal equinox. These examples emphasize important solution properties, including the need for large slew maneuvers, and they show that, even though system efficiency decreases as orbit altitude decreases, reduced path losses actually increase the amount of received energy per unit aperture area. This has significant system implications for future space solar power missions.https://resolver.caltech.edu/CaltechAUTHORS:20191224-093207317Tension-Stabilized Coiling of Isotropic Tape Springs
https://resolver.caltech.edu/CaltechAUTHORS:20190924-095350723
Year: 2020
DOI: 10.1016/j.ijsolstr.2019.09.010
A tape spring can be held tightly coiled on a circular cylinder by means of a tension force applied at the tip. This paper determines the smallest value of the required tension force by means of analytical methods, experiments and detailed numerical simulations. The minimum force depends on the coiling ratio, defined as the ratio between the transverse radius of the tape spring and the radius of the cylinder. It varies with an inverse quadratic relation for coiling ratios smaller than 1 (bending-dominated regime) and with a linear relation for coiling ratios greater than 3.424 (tension-dominated regime). For coiling ratios between 1 and 3.424 there is an intermediate behavior, and the required tension force is non-unique and rather small.https://resolver.caltech.edu/CaltechAUTHORS:20190924-095350723An Ultralight Concentrator Photovoltaic System for Space Solar Power Harvesting
https://resolver.caltech.edu/CaltechAUTHORS:20200128-142200161
Year: 2020
DOI: 10.1016/j.actaastro.2019.12.032
We present a detailed design treatment for a concentrating photovoltaic mini module subsystem with a specific power of up to 4.1 kW/kg for integration into a space solar power system. Concentrating designs are required to achieve specific power over 1 kW/kg with current high-efficiency III-V multijunction solar cells. The 15 sun, linear concentration concept detailed here reduces the system mass by replacing cell and radiation shield area with ultralight carbon fiber reinforced polymer (CFRP) optics. Reducing the cell size to 1mm width as well as careful optimization of cell architecture and CFRP material and thickness are critical for maintaining cell temperatures under 100 C despite the concentration. We also describe ultralight multilayer optical coatings to increase the thermal emissivity of the concentrator surfaces and enhance radiative transfer for cell cooling, which is a critical technological component of the total system design.https://resolver.caltech.edu/CaltechAUTHORS:20200128-142200161Nonlinear Elastic Buckling of Ultra-Thin Coilable Booms
https://resolver.caltech.edu/CaltechAUTHORS:20200720-095447666
Year: 2020
DOI: 10.1016/j.ijsolstr.2020.06.042
This paper presents a study of the elastic buckling behavior of Triangular Rollable And Collapsible (TRAC) booms under pure bending. An autoclave manufacturing process for ultra-thin composite booms is presented and the behavior of three test samples is investigated experimentally. Two regimes are observed, a pre-buckling regime and a stable post-buckling regime that ends when buckling collapse is reached. The buckling collapse moment, marking the end of the stable post-buckling regime, is typically four times higher than the initial buckling moment. A numerical simulation of the boom behavior with the Abaqus finite element package is presented and all of the features observed experimentally are captured accurately by the simulation, except buckling collapse. The numerical model is also used to study the effect of varying the boom length from 0.3 m to 5.0 m. It is shown that the pre-buckling deformation of the flanges under compression leads to a constant wavelength lateral-torsional buckling mode for which the critical moment is mostly constant across the range of lengths.https://resolver.caltech.edu/CaltechAUTHORS:20200720-095447666Shape reconstruction of planar flexible spacecraft structures using distributed sun sensors
https://resolver.caltech.edu/CaltechAUTHORS:20210104-164231438
Year: 2021
DOI: 10.1016/j.actaastro.2020.12.056
Flexible planar spacecraft, such as solar sails, phased antenna arrays and space solar power satellites vary their shape in flight and also may not have a known shape after deployment. To allow applications where spacecraft shapes are measured to allow the closed-loop correction of flight or payload parameters, this paper presents a method for measuring shapes with miniature sun sensors embedded within the structure. Two algorithms to reconstruct the shape of the structure from the two local angles to the sun are presented; the first one is geometry-based, whereas the second one uses a finite element model of the structure. Both algorithms are validated on a 1.3 m x 0.25 m structure with 14 novel miniature sun sensors with an accuracy of 5°, developed for the present research. The structure was reconstructed to an accuracy better than one millimeter by both algorithms, after undergoing bending and torsional deformations. While the geometrically based algorithm is fast and accurate for small deformations, the finite element based algorithm performs better overall, especially for larger deformations.https://resolver.caltech.edu/CaltechAUTHORS:20210104-164231438Size effects in plain-weave Astroquartz® deployable thin shells
https://resolver.caltech.edu/CaltechAUTHORS:20210713-174100812
Year: 2021
DOI: 10.1177/0021998320987618
The general scaling trend for brittle materials, in which the strength increases when the sample size decreases, is reversed in plain-weave laminates of Astroquartz® and cyanate ester resin. Specifically, both the shear stiffness and the compressive strength decrease for test samples with widths smaller than 15 times the wavelength of the fabric, and observations at the microscale explain this behavior. The derived scaling is applied to the analysis of a deployable thin shell forming a 90∘ corner hinge with five cutouts on each side. The cutouts leave narrow strips of material with width as small as one fabric wavelength, forming structural ligaments whose strength and stiffness are subject to strong size-scaling effects. A numerical simulation of the folding process followed by a failure analysis is presented, using two alternative material models and failure criteria. The size independent model predicts that the structure will remain damage-free after it is folded and deployed, whereas the size-scaled model predicts that failure will occur. The correctness of the size-scaled model prediction is verified by measuring localized damage in a physical prototype, using x-ray CT scans.https://resolver.caltech.edu/CaltechAUTHORS:20210713-174100812Topology and Shape Optimization of Ultrathin Composite Self-Deployable Shell Structures with Cutouts
https://resolver.caltech.edu/CaltechAUTHORS:20210518-073404833
Year: 2021
DOI: 10.2514/1.j059550
This paper presents two methods to design cutouts that allow damage-free folding of the stiffest possible composite self-deployable thin shell structures of complex shapes. The first method uses level-set functions that define a general number of cutouts. The second method uses a spline representation of the contour of a single cutout and optimizes its shape. Material failure detection is implemented in the solution. Both methods are applied to the design of deployable thin shells forming 90° joints, and multiple viable solutions are obtained. Experiments on the best performing design, a 90–390 μm thick shell made of Astroquartz with a cyanate ester matrix, with five cutouts on each side, are presented to illustrate and validate the proposed approach.https://resolver.caltech.edu/CaltechAUTHORS:20210518-073404833Inextensible Surface Reconstruction Under Small Relative Deformations from Distributed Angle Measurements
https://resolver.caltech.edu/CaltechAUTHORS:20220126-901981200
Year: 2022
DOI: 10.1007/s11263-021-01552-x
A mathematical model to measure the shape of a 3D surface using angle measurements from embedded sensors is presented. The surface is known in a reference configuration and is assumed to have deformed inextensibly to its current shape. An inextensibility condition is enforced through a discretization of the metric tensor generating a finite number of constraints. This model allows to parameterize the shape of the surface using a small number of unknowns which leads to a small number of sensors. We study the singularities of the equations and derive necessary conditions for the problem to be well-posed as well as limitations of the algorithm. Simulations and experiments are performed on developable surfaces under relatively small deformations to analyze the performance of the method and to show the influence of the parameters used in our algorithm. Overall, the proposed method outperforms the current state-of-the-art by almost an order of magnitude.https://resolver.caltech.edu/CaltechAUTHORS:20220126-901981200Probing the Stability of Ladder-Type Coilable Space Structures
https://resolver.caltech.edu/CaltechAUTHORS:20220112-107090239
Year: 2022
DOI: 10.2514/1.j060820
This paper analyzes the buckling and postbuckling behavior of ultralight ladder-type coilable structures, called strips, composed of thin-shell longerons connected by thin rods. Based on recent research on the stability of cylindrical and spherical shells, the stability of strip structures loaded by normal pressure is studied by applying controlled perturbations through localized probing. A plot of these disturbances for increasing pressure is the stability landscape for the structure, which gives insight into the structure's buckling, postbuckling, and sensitivity to disturbances. The probing technique is generalized to higher-order bifurcations along the postbuckling path, and low-energy escape paths into buckling that cannot be predicted by a classical eigenvalue formulation are identified. It is shown that the stability landscape for a pressure-loaded strip is similar to the landscape for classical shells, such as the axially loaded cylinder and the pressure-loaded sphere. Similarly to classical shells, the stability landscape for the strip shows that an early transition into buckling can be triggered by small disturbances; however, while classical shell structures buckle catastrophically, strip structures feature a large stable postbuckling range.https://resolver.caltech.edu/CaltechAUTHORS:20220112-107090239Investigation of Equatorial Medium Earth Orbits for Space Solar Power
https://resolver.caltech.edu/CaltechAUTHORS:20211217-98213000
Year: 2022
DOI: 10.1109/taes.2021.3122790
Most existing space solar power concepts place one or more power stations in geosynchronous Earth orbit (GEO). However, due to the limited availability of GEO orbital slots, it may not be feasible to locate a power station in GEO. To overcome this limitation, this article presents a system analysis for a space solar power system that incorporates a constellation of power stations in a 20184 km altitude equatorial medium Earth orbit (MEO). The orbiting power stations are based on the Caltech Space Solar Power Project architecture. The constellation consists of multiple power stations in a shared equatorial MEO each transmitting to a nonequatorial receiving station. The analysis assumes a one-to-one correspondence between the number of power stations and the number of ground stations. Like a GEO-based system, this constellation architecture enables a MEO-based system to provide near continuous power (outside of eclipse) to each ground station. It is shown that a MEO constellation with three or more power stations provides comparable transmission efficiency to a GEO-based system. The levelized cost of electricity (LCOE) is then computed for MEO systems with three, four, and five power stations and compared to the LCOE for the GEO-based system. Ground station area is identified as a significant contributor to the LCOE for the MEO-based systems. The system analysis shows that a MEO constellation with as few as four power stations has an LCOE comparable to GEO, and hence, it is concluded that MEO is a viable alternative to GEO for space solar power.https://resolver.caltech.edu/CaltechAUTHORS:20211217-98213000Deployment Dynamics of Thin-Shell Space Structures
https://resolver.caltech.edu/CaltechAUTHORS:20220204-680152000
Year: 2022
DOI: 10.2514/1.a35172
This study was motivated by the desire to develop accurate simulation models for the deployment dynamics of future, ultralight deployable structures consisting of multiple thin shells packaged elastically, through a combination of folding and coiling. The specific problem studied is the packaging and unconstrained deployment of a rectangular space frame formed by two thin-shell longerons connected by multiple transverse rods, and called a strip. The study included experiments on high-quality test articles, using a suspension system with low inertia and friction. The elastic folds in the strips were tracked with high-speed three-dimensional digital image correlation for deployment in both air and near-vacuum. The study also developed a high-fidelity finite element model of the strips that captures the elastic, localized deformation that occurs during the initial folding, the self-contact between different parts of the structure as the folding develops, and the strain energy stored during the folding process. This model accurately captured the deployment dynamics and self-latching of the strips, as well as the effects of air on deployment.https://resolver.caltech.edu/CaltechAUTHORS:20220204-680152000Kirigami tiled surfaces with multiple configurations
https://resolver.caltech.edu/CaltechAUTHORS:20221128-494241100.10
Year: 2022
DOI: 10.1098/rspa.2022.0405
This paper presents new kirigami patterns consisting of tiles connected by sub-folds that can approximate multiple specified target surfaces. The curvature of the surfaces approximated by the tiles varies as the patterns are folded, allowing access to a wide range of curvatures. A numerical framework is developed for the synthesis of the fold patterns that approximate a given set of target surfaces. The pattern synthesis process is framed as a tile placement problem, where compatible tile arrangements associated with each target surface are computed by solving a constrained optimization problem. After computing a set of tile arrangements, sub-folds are added to connect adjacent tiles. The resulting patterns are rigid foldable with many kinematic degrees of freedom, allowing them to achieve configurations that approximate the specified target surfaces. Kinematic simulations verify the existence of continuous paths between the target surfaces. A prototype pattern with six target surfaces is fabricated using three-dimensional printed components.https://resolver.caltech.edu/CaltechAUTHORS:20221128-494241100.10Mass efficiency of strip-based coilable space structures
https://resolver.caltech.edu/CaltechAUTHORS:20220728-729497000
Year: 2022
DOI: 10.1016/j.ijsolstr.2022.111867
This paper presents a general semi-analytical study of the mass efficiency of coilable plate-like space structures. A bending architecture based on four diagonal booms that support parallel strips is compared to a cable-stayed architecture in which vertical booms and cable stays support the diagonal booms at the tip. Limiting conditions of global buckling, local buckling, material failure, and excessive deflection define the design space for each architecture. Considering pressure loads spanning several orders of magnitude, the optimal areal density of structures of size varying from a few meters to hundreds of meters is determined for both architectures. Design charts for optimal designs are provided for a range of sizes, loads, and deflection limits. It is shown that the cable-stayed architecture is always lighter than the bending architecture, from a few percent to over 30%.https://resolver.caltech.edu/CaltechAUTHORS:20220728-729497000Probing the stability of thin-shell space structures under bending
https://resolver.caltech.edu/CaltechAUTHORS:20220706-534199000
Year: 2022
DOI: 10.1016/j.ijsolstr.2022.111806
The stability of lightweight space structures composed of longitudinal thin-shell elements connected transversely by thin rods is investigated, extending recent work on the stability of cylindrical and spherical shells. The role of localization in the buckling of these structures is investigated and early transitions into the post-buckling regime are unveiled using a probe that locally displaces the structure. Multiple probe locations are studied and the probe force versus probe displacement curves are analyzed and plotted to assess the structure's stability. The probing method enables the computation of the energy input needed to transition early into a post-buckling state, which is central to determining the critical buckling mechanism for the structure. A stability landscape is finally plotted for the critical buckling mechanism. It gives insight into the post-buckling stability of the structure and the existence of localized post-buckling states in the close vicinity of the fundamental equilibrium path.https://resolver.caltech.edu/CaltechAUTHORS:20220706-534199000Formation and propagation of buckles in coilable cylindrical thin shells with a thickness discontinuity
https://resolver.caltech.edu/CaltechAUTHORS:20221209-478595000.2
Year: 2022
DOI: 10.1016/j.ijsolstr.2022.112010
This paper studies the snap-through buckling that occurs ahead of the coiled region in thin, linear-elastic, isotropic coilable cylindrical shells with a sudden change in the thickness of the shell cross section. The study is focused on Triangular Rollable And Collapsible (TRAC) booms. It is shown that coiling of these shells leads to longitudinal compression of the inner flange mid-surface, which in turn leads to the formation of a buckle in the transition region between the fully coiled and fully deployed parts of the inner flange. This buckle grows to reach a steady-state configuration and is then pushed along the shell without changing its shape when the shell is coiled.https://resolver.caltech.edu/CaltechAUTHORS:20221209-478595000.2Multi-configuration rigidity: Theory for statically determinate structures
https://authors.library.caltech.edu/records/4zrv0-w5y55
Year: 2023
DOI: 10.1016/j.ijsolstr.2023.112502
<div class="Abstracts u-font-serif text-s">
<div class="abstract author">
<div>
<p>This paper introduces the concept of multi-configuration rigidity for kinematically indeterminate structures with elastic springs and unilateral constraints. A simple example is provided by a structure with a single mechanism and a spring that engages two different unilateral constraints. In each of these configurations, the structure can rigidly support loads up to a critical magnitude at which the unilateral constraints become inactive. The general design problem of embedding springs throughout a structure to achieve <em>multi-configuration rigidity</em>, with multiple unilateral constraints and springs, is studied. This problem is cast as a <a class="topic-link" title="Learn more about linear program from ScienceDirect's AI-generated Topic Pages" href="https://www.sciencedirect.com/topics/engineering/linear-program">linear program</a> that maximizes the critical loads required to break free from the unilateral constraints, in all target configurations. This problem can be efficiently solved with guarantees of <a class="topic-link" title="Learn more about optimality from ScienceDirect's AI-generated Topic Pages" href="https://www.sciencedirect.com/topics/engineering/optimality">optimality</a>. The formulation is generally applicable to a variety of discrete structures (e.g., linkages, pin-jointed bars, or origami) with unilateral constraints (e.g., contacts or cables).</p>
</div>
</div>
</div>
<ul class="issue-navigation u-margin-s-bottom u-bg-grey1"></ul>https://authors.library.caltech.edu/records/4zrv0-w5y55Folding kinematics of kirigami-inspired space structures
https://authors.library.caltech.edu/records/bja23-yz438
Year: 2024
DOI: 10.1016/j.ijsolstr.2024.112865
<div class="Abstracts u-font-serif text-s">
<div class="abstract author">
<div>
<p>This paper studies the folding of square, kirigami-inspired space structures consisting of concentrically arranged modular elements formed by thin shells. Localized elastic folds are introduced in the thin shells and different folding strategies can be obtained by varying the location of the folds and the sequence of imposed rotations. Modeling each modular element with rigid rods connected by revolute joints, numerical simulations of the kinematics of folding are obtained, including constraints that represent folding aids and a gravity offload system. These simulations are used to study two specific packaging schemes, and the folding envelopes of a specific structure are analyzed to identify the scheme that is easier to implement in practice. This particular scheme is demonstrated by means of a physical prototype.</p>
</div>
</div>
</div>
<div class="Keywords u-font-serif text-s">
<div class="keywords-section"></div>
</div>https://authors.library.caltech.edu/records/bja23-yz438