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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenThu, 30 Nov 2023 19:59:07 +0000Unstable kinetic relations and the dynamics of solid-solid phase transitions
https://resolver.caltech.edu/CaltechAUTHORS:20141022-084738427
Authors: Rosakis, Phoebus; Knowles, James K.
Year: 1997
DOI: 10.1016/S0022-5096(97)00026-4
In recent continuum-mechanical models of phase transitions in solids, the kinetic relation for a transition is usually assumed to be such that the driving force acting on a phase boundary is a monotonically increasing function of phase boundary velocity. The present paper explores the implications of relinquishing this assumption in the dynamics of one-dimensional elastic bars undergoing stress-induced transitions. Among other results, it is found that, for a class of non-monotonic kinetic relations, models of the kind discussed here permit stick-slip motions of a phase boundary, as observed in certain experiments.https://authors.library.caltech.edu/records/3th1t-p7j59Continuum models for irregular phase boundary motion in shape-memory tensile bars
https://resolver.caltech.edu/CaltechAUTHORS:20141021-110039001
Authors: Rosakis, Phoebus; Knowles, James K.
Year: 1999
DOI: 10.1016/S0997-7538(99)80001-1
We consider quasi-static displacement-controlled loading through one stress cycle of a shape-memory tensile bar modeled as a one-dimensional, two-phase elastic solid. Our objective is to explore the effect on the associated hysteresis loop of various qualitatively different types of kinetic relations, bearing in mind certain features of such loops that have been observed experimentally. We show that when the model involves a kinetic relation that is 'unstable' in a definite sense, 'stick-slip' motion of the interface between phases and serration of the accompanying stress-elongation curve are both predicted at slow elongation rates. We also show that a 'nonhomogeneous' kinetic relation intended to model the effect of micro-obstacles on interface motion also leads to irregular interface motion and a serrated stress-elongation curve, in this case at all elongation rates.https://authors.library.caltech.edu/records/k1ecg-h5q92A Thermodynamic Internal Variable Model for the Partition of Plastic Work into Heat and Stored Energy in Metals
https://resolver.caltech.edu/CaltechAUTHORS:20150226-170425585
Authors: Rosakis, P.; Rosakis, A. J.; Ravichandran, G.; Hodowany, J.
Year: 2000
DOI: 10.1016/S0022-5096(99)00048-4
The energy balance equation for elastoplastic solids includes heat source terms that govern the conversion of some of the plastic work into heat. The remainder contributes to the stored energy of cold work due to the creation of crystal defects. This paper is concerned with the fraction β of the rate of plastic work converted into heating. We examine the status of the common assumption that β is a constant with regard to the thermodynamic foundations of thermoplasticity and experiments. A general internal-variable theory is introduced and restricted to abide by the second law of thermodynamics. Experimentally motivated assumptions reduce this theory to a special model of classical thermoplasticity. The only part of the internal energy not determined from the isothermal response is the stored energy of cold work, a function only of the internal variables. We show that this function can be inferred from stress and temperature data from a single adiabatic straining experiment. Experimental data from dynamic Kolsky-bar tests at various strain rates yield a unique stored energy function. Its knowledge is crucial for the determination of the thermomechanical response in non-isothermal processes. Such a prediction agrees well with results from dynamic tests at different rates. In these experiments, β is found to depend strongly on both strain and strain rate for various engineering materials. The model is successful in predicting this dependence. Requiring β to be constant is thus an approximation of dubious validity.https://authors.library.caltech.edu/records/bzdz6-0yd40Partition of Plastic Work into Heat and Stored Energy in Metals
https://resolver.caltech.edu/CaltechAUTHORS:20150226-165652488
Authors: Hodowany, J.; Ravichandran, G.; Rosakis, A. J.; Rosakis, P.
Year: 2000
DOI: 10.1007/BF02325036
This study investigates heat generation in metals during plastic deformation. Experiments were designed to measure the partition of plastic work into heat and stored energy during dynamic deformations under adiabatic conditions. A servohydraulic load frame was used to measure mechanical properties at lower strain rates, 10^(−3) s^(−1) to 1 s^(−1). A Kolsky pressure bar was used to determine mechanical properties at strain rates between 10^3 s^(−1) and 10^4 s^(−1). For dynamic loading, in situ temperature changes were measured using a high-speed HgCdTe photoconductive detector. An aluminum 2024-T3 alloy and α-titanium were used to determine the dependence of the fraction of plastic work converted to heat on strain and strain rate. The flow stress and β for 2024-T3 aluminum alloy were found to be a function of strain but not strain rate, whereas they were found to be strongly dependent on strain rate for α-titanium.https://authors.library.caltech.edu/records/7hhd9-rr083On the Conversion of Plastic Work into Heat During High-Strain-Rate Deformation
https://resolver.caltech.edu/CaltechAUTHORS:RAVaipcp02
Authors: Ravichandran, Guruswami; Rosakis, Ares J.; Hodowany, Jon; Rosakis, 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-q2t55A model for compression-weakening materials and the elastic fields due to contractile cells
https://resolver.caltech.edu/CaltechAUTHORS:20151218-112112538
Authors: Rosakis, Phoebus; Notbohm, Jacob; Ravichandran, Guruswami
Year: 2015
DOI: 10.1016/j.jmps.2015.08.013
We construct a homogeneous, nonlinear elastic constitutive law that models aspects of the mechanical behavior of inhomogeneous fibrin networks. Fibers in such networks buckle when in compression. We model this as a loss of stiffness in compression in the stress–strain relations of the homogeneous constitutive model. Problems that model a contracting biological cell in a finite matrix are solved. It is found that matrix displacements and stresses induced by cell contraction decay slower (with distance from the cell) in a compression weakening material than linear elasticity would predict. This points toward a mechanism for long-range cell mechanosensing. In contrast, an expanding cell would induce displacements that decay faster than in a linear elastic matrix.https://authors.library.caltech.edu/records/yp183-47g88Microbuckling of Fibrous Matrices Enables Long Range Cell Mechanosensing
https://resolver.caltech.edu/CaltechAUTHORS:20161108-141109524
Authors: Burkel, Brian; Lesman, Ayelet; Rosakis, Phoebus; Tirrell, David A.; Ravichandran, Guruswami; Notbohm, Jacob
Year: 2016
DOI: 10.1007/978-3-319-41351-8_19
When biological cells migrate, divide, and invade, they push and pull on individual fibers of the matrix surrounding them. The resulting fiber displacements are neither uniform nor smooth; rather, displacements localize to form dense fibrous bands that span from one cell to another. It is thought that these bands may be a mechanism by which cells can sense their neighbors, but this hypothesis remains untested, because the mechanism for band formation remains unknown. Using digital volume correlation, we measure the displacements induced by contractile cells embedded in a fibrous matrix. We find that cell-induced displacements propagate over a longer range than predicted by linear elasticity. To explain the long-range propagation of displacements, we consider the effect of buckling of individual matrix fibers, which generates a nonlinear stress-strain relationship. We show that fiber buckling is the mechanism that causes the displacements to propagate over a long range and the bands to form between nearby cells. The results thus show that buckling of individual fibers provides a mechanism by which cells may sense their distant neighbors mechanically.https://authors.library.caltech.edu/records/gwm7t-v3507