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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, the authors studied suspensions of monodisperse spheres dispersed in a liquid polymer have been studied in shear flow, and measured properties include linear dynamic moduli, steady-state shear viscosities, and nonlinear stress relaxation moduli.
Abstract: Suspensions of monodisperse spheres dispersed in a liquid polymer have been studied in shear flow. The particle diameters range from 0.18 to 2.7 μm. The measured properties include linear dynamic moduli, steady-state shear viscosities, and nonlinear stress relaxation moduli. At small volume fractions and/or large particle sizes, the linear and nonlinear behavior can be explained on the basis of hydrodynamic effects caused by the presence of the particles. In that case, the nonlinear relaxation moduli display time−strain separability. The concentration dependence of the damping function at large strains is similar to that of the linear properties. At small interparticle distances, a weak particulate structure develops that mainly alters the low shear viscosities and the low-frequency moduli. The effect of this structure on the stresses can be gradually eliminated by applying larger strains, as demonstrated by the strain dependence of the nonlinear relaxation moduli in step−strain experiments.

70 citations

Journal ArticleDOI
TL;DR: Results emphasize that fluid-flow dependent viscoelasticity dominates the compressive response of cartilage, whereas intrinsic solid matrix viscoeling dominates the tensile response.
Abstract: Very limited information is currently available on the constitutive modeling of the tensile response of articular cartilage and its dynamic modulus at various loading frequencies. The objectives of this study were to (1) formulate and experimentally validate a constitutive model for the intrinsic viscoelasticity of cartilage in tension, (2) confirm the hypothesis that energy dissipation in tension is less than in compression at various loading frequencies, and (3) test the hypothesis that the dynamic modulus of cartilage in unconfined compression is dependent upon the dynamic tensile modulus. Experiment 1: Immature bovine articular cartilage samples were tested in tensile stress relaxation and cyclical loading. A proposed reduced relaxation function was fitted to the stress-relaxation response and the resulting material coefficients were used to predict the response to cyclical loading. Adjoining tissue samples were tested in unconfined compression stress relaxation and cyclical loading. Experiment 2: Tensile stress relaxation experiments were performed at varying strains to explore the strain-dependence of the viscoelastic response. The proposed relaxation function successfully fit the experimental tensile stress-relaxation response, with R2 = 0.970+/-0.019 at 1% strain and R2 = 0.992+/-0.007 at 2% strain. The predicted cyclical response agreed well with experimental measurements, particularly for the dynamic modulus at various frequencies. The relaxation function, measured from 2% to 10% strain, was found to be strain dependent, indicating that cartilage is nonlinearly viscoelastic in tension. Under dynamic loading, the tensile modulus at 10 Hz was approximately 2.3 times the value of the equilibrium modulus. In contrast, the dynamic stiffening ratio in unconfined compression was approximately 24. The energy dissipation in tension was found to be significantly smaller than in compression (dynamic phase angle of 16.7+/-7.4 deg versus 53.5+/-12.8 deg at 10(-3) Hz). A very strong linear correlation was observed between the dynamic tensile and dynamic compressive moduli at various frequencies (R2 = 0.908+/-0.100). The tensile response of cartilage is nonlinearly viscoelastic, with the relaxation response varying with strain. A proposed constitutive relation for the tensile response was successfully validated. The frequency response of the tensile modulus of cartilage was reported for the first time. Results emphasize that fluid-flow dependent viscoelasticity dominates the compressive response of cartilage, whereas intrinsic solid matrix viscoelasticity dominates the tensile response. Yet the dynamic compressive modulus of cartilage is critically dependent upon elevated values of the dynamic tensile modulus.

70 citations

Journal ArticleDOI
TL;DR: In this paper, the authors measured biaxial stress and strain in (100) and (111) oriented grains and observed that grain growth was controlled by strain energy density minimization.
Abstract: Biaxial stress and strain in (100) and (111) oriented grains have been measured as a function of annealing temperature for a Cu film on an oxidized Si substrate which exhibits abnormal (100) grain growth. The observed behavior indicates isostrain averaging, which is consistent with grain growth that is controlled by strain energy density minimization. In contrast, two films which do not exhibit (100) abnormal grain growth appear to follow isostress averaging. Strain energy density minimization in this situation favors (111) grain growth.

70 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the role of interlayer water in the mechanical behavior of calcium silicate hydrate (C-S-H) and showed that a significant part of the relaxation at saturation is attributed to the hydrodynamic component associated with the pore water.
Abstract: The origin of the time-dependent response of cement-based materials to applied stress has not been clearly resolved. The role of interlayer water in the mechanical behavior of calcium silicate hydrate (C–S–H) is still debated. In order to better understand the pertinent mechanisms, the stress relaxation tests were conducted on thin rectangular beams of compacted synthetic C–S–H powder and hydrated Portland cement subjected to three-point bending. C–S–H specimens of variable composition (C/S = 0.8, 1.2 and 1.5) were prepared at various moisture content levels from saturation to the dry state. A special drying procedure was applied in order to remove the adsorbed and interlayer water incrementally from C–S–H conditioned at 11%RH. It was shown that a significant part of the relaxation at saturation is attributed to the hydrodynamic component associated with the pore water. It was demonstrated that the viscoelastic performance of C–S–H depends considerably on the presence of interlayer water. It was argued that the results support the validity of the theory of sliding of C–S–H sheets as a time-dependent deformation mechanism responsible for the creep and stress relaxation of cement-based materials. This concept was illustrated in a proposed model for the viscoelastic response of C–S–H.

70 citations

Journal Article
TL;DR: Collagen viscoelasticity appears to play an import role in articular cartilage in tensile testing, while fluid pressurization dominates the transient mechanical behavior in compression.

70 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023145
2022390
2021266
2020276
2019270
2018281