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Stress relaxation
About: Stress relaxation is a research topic. Over the lifetime, 12959 publications have been published within this topic receiving 270815 citations.
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TL;DR: In this paper, a new set of physically based, unified ageing-creep constitutive equation is developed based on the unified theories and ageing kinetics and the material constants within the equations are determined from experimental results and evolutionary algorithm (EA) based optimization package.
106 citations
TL;DR: In this paper, a model for the development of cross-hatch surface morphology in growing mismatched layers is proposed and investigated, which incorporates two important elements: (i) strain relaxation due to dislocation glide in the layer interior that is also associated with misfit dislocation formation at the film/substrate interface and (ii) lateral surface transport that eliminates surface steps that originated from dislocation drift.
Abstract: We propose and investigate a model for the development of cross-hatch surface morphology in growing mismatched layers. The model incorporates two important elements: (i) strain relaxation due to dislocation glide in the layer (film) interior that is also associated with misfit dislocation formation at the film/substrate interface and (ii) lateral surface transport that eliminates surface steps that originated from dislocation glide. A combination of dislocation-assisted strain relaxation and surface step flow leads to the appearance of surface height undulations during layer growth. A Monte Carlo simulation technique was applied to model dislocation nucleation events in the course of strain relaxation. The simulation was used to model the influence of dislocations on film surface height profiles. The surface height displacement was calculated from the analytic elasticity solutions for edge dislocations near a free surface. The results of the modeling predict that the average amplitude of the surface undulations and their apparent wavelength both increase with increasing film relaxation and film thickness. The developed cross-hatch pattern is characterized by an atomically smooth but mesoscopically (lateral dimensions ∼0.1–10 μm) rough surface morphology. The conclusions of the model are in agreement with atomic force microscopy observations of cross-hatch surface relief in In0.25Ga0.75As/GaAs samples grown well beyond the critical thickness for misfit dislocation formation.
106 citations
TL;DR: Simple, but accurate, asymptotic approximations are derived for the deformation and stress fields in the tissue for slow and moderately fast rates of compression and lead to important insights into the role of the flow-dependent viscoelastic nature of articular cartilage and other hydrated biological tissues.
Abstract: The dominant mechanism giving rise to the viscoelastic response of articular cartilage during compression is the nonlinear diffusive interaction of the fluid and solid phases of the tissue as they flow relative to one another. The present study is concerned with the role of this interaction under uniaxial stress relaxation in compression. The model is a biphasic mixture of fluid and solid which incorporates the strain-dependent permeability found earlier from permeation experiments. When a ramp-displacement is imposed on the articular surface, simple, but accurate, asymptotic approximations are derived for the deformation and stress fields in the tissue for slow and moderately fast rates of compression. They are shown to agree very well with experiment and they provide a simple means for determining the material parameters. Moreover, they lead to important insights into the role of the flow-dependent viscoelastic nature of articular cartilage and other hydrated biological tissues.
106 citations
TL;DR: In this paper, a soda-lime-silica glass was subjected to an ordinary ion exchange treatment in molten potassium nitrate at temperatures near and substantially below the strain point of the glass.
Abstract: A soda-lime-silica glass was subjected to an ordinary ion exchange treatment in molten potassium nitrate at temperatures near and substantially below the strain point of the glass. Stress profiles were measured as a function of exchange temperature and time. At all temperatures, the measurements showed rapid relaxation of the surface stress and the development of a pronounced compression maximum in a short period. A simple viscoelastic model with composition-independent parameters was used to analyze the stress profiles. Neither Maxwell's nor Michelson's relaxation expression could satisfy both characteristics of the residual stress development. Reasons for discrepancies are discussed.
106 citations
TL;DR: In this article, a qualitative process zone model is proposed to explain the effect of ferroelastic domain switching on the R-curve of the barium titanate in CT-specimens.
Abstract: R-curves of ferroelectric barium titanate have been measured with CT-specimens. Depending on the grain size, the R-curves exhibit an increase from an initial value of 0.5–0.7 MPa√m to a plateau value of 0.7–1.2 MPa√m after a crack length increment of approximately 100–800 μm. The main toughening mechanism is thought to be ferroelastic domain switching leading to the development of a process zone around the crack. The small differences in the initial values of the R-curves are attributed to grain bridging, crack deflection and crack branching associated with large grains. Applying an electric field perpendicular to the specimen plane results in an increased initial fracture toughness and a stronger R-curve behaviour. Time-dependent reorientation of domains in the crack wake causes stress relaxation combined with a strong time dependence of the R-curves. A qualitative process zone model is proposed to explain these effects.
105 citations