Book Section records
https://feeds.library.caltech.edu/people/Rosakis-A-J/book_section.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenWed, 07 Feb 2024 02:51:10 +0000Interpretation of optical caustic patterns obtained during unsteady crack growth: an analysis based on a higher-order transient expansion
https://resolver.caltech.edu/CaltechAUTHORS:20190221-110520782
Authors: {'items': [{'id': 'Liu-Cheng', 'name': {'family': 'Liu', 'given': 'Cheng'}}, {'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'Ares J.'}, 'orcid': '0000-0003-0559-0794'}]}
Year: 1991
DOI: 10.1117/12.49532
The optical caustic method is re-examined considering the presence of transient effects. Based on the higher-order asymptotic expansion provided by Freund and Rosakis, regarding the stress field near a non-uniformly propagating crack tip, the caustic mapping and the initial curve equations are derived. The dynamic stress intensity factor, K^d_I(t), is related to experimentally measurable quantities of the caustic pattern by an explicit expression. It is shown that the classical analysis of caustics is a special case of the new interpretation method. The Broberg problem is used as an example problem to check the feasibility of analysing caustics in the presence of higher-order transient terms. It is shown that the caustic patterns are sensitive to transient effects, and that use of the classical analysis of caustics in the interpretation of the optical patterns for this problem may result in large errors in the value of the stress intensity factor, especially at short times after initiation.https://authors.library.caltech.edu/records/ack8r-qbt11Experimental investigation of dynamic mixed-mode fracture initiation
https://resolver.caltech.edu/CaltechAUTHORS:20190221-110520608
Authors: {'items': [{'id': 'Lambros-J-M', 'name': {'family': 'Lambros', 'given': 'J.'}}, {'id': 'Mason-J-J', 'name': {'family': 'Mason', 'given': 'J. J.'}}, {'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'A. J.'}, 'orcid': '0000-0003-0559-0794'}]}
Year: 1991
DOI: 10.1117/12.49481
The use of a coherent gradient sensing (CGS) apparatus is explored in dynamic fracture mechanics investigations. The ability of the method to accurately quantify mixed-mode crack tip deformation fields is tested under dynamic loading conditions. The specimen geometry and loading follow that of Lee and Freund who give the theoretical and numerical mixed mode K values as a function of time for the testing conditions. The CGS system's measurements of KI and KII are compared with the predicted results, and good agreement is found.https://authors.library.caltech.edu/records/6xgdj-ghr74Crack-tip deformation field measurements using coherent gradient sensing
https://resolver.caltech.edu/CaltechAUTHORS:20190221-110520688
Authors: {'items': [{'id': 'Tippur-H-V', 'name': {'family': 'Tippur', 'given': 'Hareesh V.'}}, {'id': 'Krishnaswamy-S', 'name': {'family': 'Krishnaswamy', 'given': 'Sridhar'}}, {'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'Ares J.'}, 'orcid': '0000-0003-0559-0794'}]}
Year: 1991
DOI: 10.1117/12.49513
A real time, full field, lateral shearing interferometry - coherent gradient sensing (CGS) - has recently been developed for investigating fracture in transparent and opaque solids. The resulting interference patterns are related to the mechanical fields by means of a first order diffraction analysis. The method has been successfully applied to quasi-static and dynamic crack tip deformation field mapping in homogeneous and bimaterial fracture specimens.https://authors.library.caltech.edu/records/cyp7x-a0095Dynamically Growing Shear Bands in Metals: A Study of Transient Temperature and Deformation Fields
https://resolver.caltech.edu/CaltechAUTHORS:20201201-105030731
Authors: {'items': [{'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'A. J.'}, 'orcid': '0000-0003-0559-0794'}, {'id': 'Ravichandran-G', 'name': {'family': 'Ravichandran', 'given': 'G.'}, 'orcid': '0000-0002-2912-0001'}, {'id': 'Zhou-M', 'name': {'family': 'Zhou', 'given': 'M.'}}]}
Year: 1997
DOI: 10.1007/978-94-011-5642-4_14
The objective of our work is (1) to establish the critical conditions for initiation and growth of shear bands in pre-notched plates subjected to asymmetric impact loading (dynamic mode II, see Fig. 1); and (2) to investigate and characterize the transition in the modes of failure when such plates are subjected to a variety of loading rates (impact velocities). These failure modes which may feature either dynamic shear band growth, dynamic crack propagation or both, (see Fig. 1), have been observed in structural materials such as the high strength steels and heat-resistant titanium alloy considered in the present work. The approach is to study both the dynamic mechanical deformations and the processes of heat generation and thermal softening. This necessitates the simultaneous use of high speed optical and infrared diagnostics in the experiments. In parallel to the experimental study, full-scale thermomechanical finite element simulations are conducted to assist the development of criteria for shear band initiation and propagation. The calculations make use of constitutive parameters measured in house through material testing in a variety of strain rates. Such a combined experimental and numerical approach enables us to make direct comparisons between measurements and predictions obtained using various material constitutive and failure models.https://authors.library.caltech.edu/records/c33gk-64k25Experimental and Numerical Investigation of Shear-dominated Intersonic Crack Growth and Friction in Unidirectional Composites
https://resolver.caltech.edu/CaltechAUTHORS:20200219-114918280
Authors: {'items': [{'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'A. J.'}, 'orcid': '0000-0003-0559-0794'}, {'id': 'Yu-Chengxiang-Rena', 'name': {'family': 'Yu', 'given': 'C.'}, 'orcid': '0000-0003-4176-0324'}, {'id': 'Ortiz-M', 'name': {'family': 'Ortiz', 'given': 'M.'}, 'orcid': '0000-0001-5877-4824'}, {'id': 'Coker-D', 'name': {'family': 'Coker', 'given': 'D.'}, 'orcid': '0000-0001-7385-7089'}, {'id': 'Pandolfi-A', 'name': {'family': 'Pandolfi', 'given': 'A.'}, 'orcid': '0000-0002-7084-7456'}]}
Year: 2002
DOI: 10.1007/0-306-48410-2_27
Dynamic crack growth in unidirectional graphite/epoxy composite materials subjected to in-plane impact loading is investigated experimentally and numerically. The experiments are conducted using CGS (Coherent Gradient Sensing) Interferometry in conjunction with high-speed photography to visualize the crack growth events. Cracks are found to propagate at subsonic speeds in the Mode-I case, whereas in both mixed mode and Mode-II the crack tip speed clearly exceeds the shear wave speed of the laminate. For these intersonically growing shear (Mode-II) cracks a shock wave emanating from the crack tip is observed. This provides direct evidence that the cracks propagate faster than the shear wave speed of the composite. The crack tip speed is initally observed to jump to a level close to the axial longitudinal wave speed along the fibers (7500 m/s) and then to stabilize to a lower level of approximately 6500 m/s. This speed corresponds to the speed at which the energy release rate required for shear crack growth is non-zero as determined from asymptotic analysis. The CGS interferograms also reveal the existence of large-scale frictional contact of the crack faces behind the moving shear cracks. In addition high speed thermographic measurements are conducted that show concentrated hot spots behind the crack tip indicating crack face frictional contact. These experiments are modeled by a detailed dynamic finite element calculation involving cohesive elements, adaptive remeshing using subdivision and edge collapse, composite elements, and penalty contact. The numerical calculations are calibrated on the basis of fundamental material properties measured in the laboratory. The computational results are found to be in excellent agreement with the optical experimental measurements (crack speed record and near tip deformation field structure). For shear crack growth, the numerics also confirm the optical observation of large-scale crack face contact.https://authors.library.caltech.edu/records/fde8n-wwd04Dynamic Crack Growth along Interfaces
https://resolver.caltech.edu/CaltechAUTHORS:20200221-133523276
Authors: {'items': [{'id': 'Needleman-A', 'name': {'family': 'Needleman', 'given': 'A.'}}, {'id': 'Coker-Demirkan', 'name': {'family': 'Coker', 'given': 'D.'}, 'orcid': '0000-0001-7385-7089'}, {'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'A. J.'}, 'orcid': '0000-0003-0559-0794'}]}
Year: 2002
DOI: 10.1007/978-94-017-0081-8_29
For remotely loaded cracks in isotropic elastic solids, the energy flux into the crack tip vanishes as the crack speed increases to the Rayleigh wave speed of the material, see [1]. However, theoretical and numerical studies dating back to the mid 1970's, e.g. Andrews [2], Burridge et al. [3] and Broberg [4, 5], have indicated that faster crack speeds should be possible under shear loading conditions.https://authors.library.caltech.edu/records/ej9tm-c3704On the Conversion of Plastic Work into Heat During High-Strain-Rate Deformation
https://resolver.caltech.edu/CaltechAUTHORS:RAVaipcp02
Authors: {'items': [{'id': 'Ravichandran-G', 'name': {'family': 'Ravichandran', 'given': 'Guruswami'}, 'orcid': '0000-0002-2912-0001'}, {'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'Ares J.'}, 'orcid': '0000-0003-0559-0794'}, {'id': 'Hodowany-J', 'name': {'family': 'Hodowany', 'given': 'Jon'}}, {'id': 'Rosakis-P', 'name': {'family': 'Rosakis', 'given': 'Phoebus'}}]}
Year: 2002
DOI: 10.1063/1.1483600
Heat generation in metals during high-strain-rate plastic deformation was investigated. Experiments were designed to measure the partition of plastic work into heat and stored energy during dynamic deformations under adiabatic conditions. A Kolsky pressure bar was used to determine mechanical properties at high strain rates while a servo-hydraulic material testing system was used at low strain rates. For dynamic loading, in-situ temperature changes were measured using a high-speed infrared detector. The dependence of the fraction of plastic work converted to heat on strain and strain rate was determined for an aluminum 2024-T3 alloy and alpha-titanium. The flow stress and the fraction of plastic work converted to heat for 2024-T3 aluminum alloy were found to be a function of strain but not of the strain rate while they were found to be strongly dependent on strain rate for alpha-titanium.https://authors.library.caltech.edu/records/y3p0p-q2t55Validation of large scale simulations of dynamic fracture
https://resolver.caltech.edu/CaltechAUTHORS:20200609-095317554
Authors: {'items': [{'id': 'Arias-I', 'name': {'family': 'Arias', 'given': 'Irene'}}, {'id': 'Knap-J', 'name': {'family': 'Knap', 'given': 'Jaroslaw'}}, {'id': 'Chalivendra-V-B', 'name': {'family': 'Chalivendra', 'given': 'Vijaya B.'}}, {'id': 'Hong-Soonsung', 'name': {'family': 'Hong', 'given': 'Soonsung'}}, {'id': 'Ortiz-M', 'name': {'family': 'Ortiz', 'given': 'Michael'}, 'orcid': '0000-0001-5877-4824'}, {'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'Ares J.'}, 'orcid': '0000-0003-0559-0794'}]}
Year: 2006
DOI: 10.1007/1-4020-5370-3_252
A novel integrated approach is developed for a systematic validation of large-scale finite element simulations on dynamic crack propagations along a weak plane [1]. A set of well-controlled experimental scheme is specifically designed to provide accurate input data for the numerical simulations as well as to provide metrics for quantitative comparisons between experimental and numerical results. Dynamic photoelasticity with high-speed photography is used to capture experimental records of dynamic crack propagations along a weak plane and to provide the crack propagation history. In the dynamic experiments, a modified Hopkinson bar setup with a notch-face loading configuration is used to obtain controlled loading conditions for the dynamic fracture problem. Also an inverse-problem approach of cohesive zone model is employed to obtain a realistic cohesive law, i.e. a traction-separation law, of the weak plane, from independently measured crack-tip deformation fields using speckle interferometry technique. The experimentally collected data, the loading conditions and the cohesive law, are considered as input for the finite element simulations [2]. We employ finite-deformation cohesive elements to account for crack initiation and growth in bulk finite-element discretizations of the experimental sample. As it is well know, the cohesive elements introduce an additional material-dependent length-scale into the finite element model. The demand of accurately resolving this length-scale by the finite-element discretization, as required for truly mesh-independent results, may often lead to discretizations containing several millions of elements. We therefore resort to massively parallel computing.
A comparison of the metrics from the numerical simulations with those from the experimental measurements is performed to validate the large-scale simulations. The numerical results show good agreements with the experimental results, leading to a successful validation of the large scale simulations of the dynamic crack propagations along the weak plane.https://authors.library.caltech.edu/records/pjwqf-qv757Dynamic Shear Rupture in Frictional Interfaces: Speeds, Directionality, and Modes
https://resolver.caltech.edu/CaltechAUTHORS:20160726-082744533
Authors: {'items': [{'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'A. J.'}, 'orcid': '0000-0003-0559-0794'}, {'id': 'Xia-K', 'name': {'family': 'Xia', 'given': 'K.'}}, {'id': 'Lykotrafitis-G', 'name': {'family': 'Lykotrafitis', 'given': 'G.'}}, {'id': 'Kanamori-H', 'name': {'family': 'Kanamori', 'given': 'H.'}, 'orcid': '0000-0001-8219-9428'}]}
Year: 2007
DOI: 10.1016/B978-0-444-53802-4.00072-5
The goal in designing dynamic frictional experiments simulating earthquake rupture has been to create a testing environment or platform which could reproduce some of the basic physics governing the rupture dynamics of crustal earthquakes while preserving enough simplicity so that clear conclusions can be obtained by pure observation. In this chapter, we first review past and recent experimental work on dynamic shear rupture propagation along frictional interfaces. The early experimental techniques are discussed in relation to recent experimental simulations of earthquakes which feature advanced diagnostics of high temporal and spatial resolution. The high-resolution instrumentation enables direct comparison between the experiments and data recorded during natural earthquakes. The experimental results presented in this chapter are examined in light of seismological observations related to various natural large rupture events and of recent theoretical and numerical development in the understanding of frictional rupture. In particular, the physics and conditions leading to phenomena such as supershear rupture growth, sub-Rayleigh to supershear rupture transition, and rupture directionality in inhomogeneous systems are discussed in detail. Finally, experiments demonstrating the attainability of various rupture modes (crack-like, pulse-like, and mixed) are presented and discussed in relation to theoretical and numerical predictions.https://authors.library.caltech.edu/records/9hm3f-5t356In-situ Optical Investigations of Hypervelocity Impact Induced Dynamic Fracture
https://resolver.caltech.edu/CaltechAUTHORS:20200522-132645095
Authors: {'items': [{'id': 'Lamberson-L-E', 'name': {'family': 'Lamberson', 'given': 'Leslie E.'}}, {'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'Ares J.'}, 'orcid': '0000-0003-0559-0794'}, {'id': 'Eliasson-V', 'name': {'family': 'Eliasson', 'given': 'Veronica'}}]}
Year: 2011
DOI: 10.1007/978-1-4419-8228-5_6
Two independent optical methods are used to analyze the dynamic material behavior of Mylar and Homalite-100 subjected to hypervelocity impact. Birefringent targets are loaded in tension inside a two-stage light-gas gun vacuum chamber, and are impacted with a 5 mg nylon slug at velocities between 3 and 6 km/s. Caustics and photoelasticity combined with high-speed photography are used to determine dynamic stress intensity behavior around the crack tip during and after impact. Homalite-100 lower crack tip speeds are subjected to reflecting boundary shear waves from the nylon impact, and thereby the crack path exhibits distinct kinks; whereas Mylar higher crack tip speeds provides distinguishable isochromatic patterns and an unadulterated fracture surface. Shear wave patterns in the target from photoelastic effects are compared to results from numerical simulations using the Overture Suite, which solves linear elasticity equations on overlapping curvilinear grids by means of adaptive mesh refinement.https://authors.library.caltech.edu/records/69vcc-ygz09Feasibility of Non-Equilibrium Hypersonic Flow Measurements at the Small Particle Hypervelocity Impact Range
https://resolver.caltech.edu/CaltechAUTHORS:20190828-102318872
Authors: {'items': [{'id': 'Alexeenko-Alina-A', 'name': {'family': 'Alexeenko', 'given': 'A. A.'}}, {'id': 'Kulakhmetov-Marat', 'name': {'family': 'Kulakhmetov', 'given': 'M.'}}, {'id': 'Weaver-Andrew', 'name': {'family': 'Weaver', 'given': 'A.'}}, {'id': 'Slipchenko-M-N', 'name': {'family': 'Slipchenko', 'given': 'M. N.'}}, {'id': 'Mihaly-J-M', 'name': {'family': 'Mihaly', 'given': 'J.'}}, {'id': 'Adams-Marc', 'name': {'family': 'Adams', 'given': 'M.'}}, {'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'A.'}, 'orcid': '0000-0003-0559-0794'}]}
Year: 2012
DOI: 10.2514/6.2012-596
Currently used hypersonic flow models, such as high-enthalpy reaction and energy relaxation rates, are based on experiments conducted at relatively low flow enthalpies and are highly uncertain. This paper presents analysis of the feasibility of calibrating hypersonic flow parameters using free-flight experiments at the Small Particle Hypervelocity Range (SPHIR) at Caltech/JPL. Chemically reacting, nonequilibrium flows around a 2-mm diameter spherical projectile are modeled using the Direct Simulation Monte Carlo (DSMC) method. The flowfields generated by DSMC simulations are used to calculate emission spectra in order to determine the observable radiation in UV/vis spectral range. Bayesian calibration and generalized polynomial chaos expansion (gPCE) techniques are used to assess the sensitivity of observable flow properties to key reaction rates. These techniques are then used to predict how experimental resolution would affect the uncertainty in the calibrated parameters.https://authors.library.caltech.edu/records/kjrbw-h2e32A Recursive Division Stochastic Strike-Slip Seismic
Source Algorithm Using Insights from Laboratory
Earthquakes
https://resolver.caltech.edu/CaltechAUTHORS:20130305-152759959
Authors: {'items': [{'id': 'Siriki-Hemanth', 'name': {'family': 'Siriki', 'given': 'H.'}}, {'id': 'Rosakis-A-J', 'name': {'family': 'Rosakis', 'given': 'A. J.'}, 'orcid': '0000-0003-0559-0794'}, {'id': 'Krishnan-Swaminathan', 'name': {'family': 'Krishnan', 'given': 'S.'}, 'orcid': '0000-0002-2594-1523'}, {'id': 'Bhat-Harsha-S', 'name': {'family': 'Bhat', 'given': 'H. S.'}}, {'id': 'Lu-Xiao', 'name': {'family': 'Lu', 'given': 'X.'}}]}
Year: 2012
There are a sparse number of credible source models available from past earthquakes and a stochastic source
model generation algorithm thus becomes necessary for robust risk quantification using scenario earthquakes.
We present an algorithm that combines the physics of fault rupture as imaged in laboratory earthquakes with
stress estimates on the fault constrained by field observations to generate probability distributions of rise-time
and rupture-speed for strike-slip earthquakes. The algorithm is validated through a statistical comparison of peak
ground velocity at 636 sites in Southern California from synthetic ground motion histories simulated for 10
rupture scenarios using a stochastically generated source model against that generated using a kinematic source
model from a finite source inversion. This model, selected from a set of 5 stochastically generated source
models, produces ground shaking intensities in Southern California with a median that is closest to the median
intensity of shaking from all 5 source models (and 10 rupture scenarios per model).https://authors.library.caltech.edu/records/m8447-nyn62