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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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15 Dec 1995TL;DR: In this article, a method of strengthening a glass article by developing compressive stress in a surface layer on the article through an exchange of alkali metal ions in the surface layer at an elevated temperature below the glass strain point is described.
Abstract: A method of strengthening a glass article by developing compressive stress in a surface layer on the article through an exchange of alkali metal ions in the surface layer at an elevated temperature below the glass strain point, the step of minimizing stress relaxation by carrying out the ion exchange in a glass essentially free from non-bridging oxygen atoms. Glasses having particular utility contain alumina in their compositions in such amount that the number of aluminum atoms in a glass are at least equal to the number of alkali metal ions, or contain both alumina and boric oxide in such amounts that the formula ##EQU1## is satisfied.
104 citations
TL;DR: In this article, the authors calculate the equilibrium stresses and strains in the substrate as well as in the deposit by using a method initiated by Hu [J. Appl. Phys. 50 (1979) 4661] where continuous forces that the deposit exerts on its substrate are calculated in a self-consistent way.
104 citations
TL;DR: A new elasto-visco-plastic model which is able to describe the mechanical properties of a concentrated cell suspension or aggregate is reported on, based on the idea that the rearrangement of adhesion bonds during the deformation of the aggregate is related to the existence of a yield stress in the macroscopic constitutive equation.
104 citations
TL;DR: In this article, the authors measured the flow stress of tungsten single crystals, oriented for single slip, in dependence on temperature and strain rate in the temperature regime 60 to 800 K by successive tensile deformations at constant strain rate and in correlated stress-relaxation tests.
Abstract: The flow stress of high-purity tungsten single crystals, oriented for single slip, was measured in dependence on temperature and strain rate in the temperature regime 60 to 800 K by successive tensile deformations at constant strain rate and in correlated stress-relaxation tests. Three regimes in the dependence of the flow stress and its strain-rate sensitivity on the temperature were detected. They constitute a challenging feature of the mechanical properties of high-purity b.c.c. metals. The interpretation of the results is based on the motion of a 0 /2(111) screw dislocations which is rate-controlled by thermally activated formation of kink pairs on screw dislocations. The kink-pair theory of the flow stress developed by A. Seeger provides excellent tools to interprete the temperature and strain-rate dependence of the flow stress of b.c.c. metals. Comparison between theory and experiment enables quantitative tests of the theory and allows the determination of kink properties. It is found that for low stresses (regime I, T > 600 K) the fundamental process of kink-pair formation takes place on {211} plane with a formation enthalpy of two isolated kinks of a kink pair 2H k ≅ 2.1 eV. For intermediate stresses (regime II, 220 K ≤ T ≤ 600 K) the fundamental kink-pair formation process takes place on {211} with 2H k ≅ 1.75 eV. For high stresses (regime III, T ≤ 220K) the fundamental process of kink-pair formation takes place on {110} glide planes with 2H k ≅ 1.3eV.
104 citations
TL;DR: In this paper, a thermomechanical constitutive model was developed for the time-dependent behaviors of the glass transition of amorphous networks, which used multiple discrete relaxation processes to describe the distribution of relaxation times for stress relaxation, structural relaxation, and stress-activated viscous flow.
Abstract: In this paper, a thermomechanical constitutive model was developed for the time-dependent behaviors of the glass transition of amorphous networks. The model used multiple discrete relaxation processes to describe the distribution of relaxation times for stress relaxation, structural relaxation, and stress-activated viscous flow. A non-equilibrium thermodynamic framework based on the fictive temperature was introduced to demonstrate the thermodynamic consistency of the constitutive theory. Experimental and theoretical methods were developed to determine the parameters describing the distribution of stress and structural relaxation times and the dependence of the relaxation times on temperature, structure, and driving stress. The model was applied to study the effects of deformation temperatures and physical aging on the shape-memory behavior of amorphous networks. The model was able to reproduce important features of the partially constrained recovery response observed in experiments. Specifically, the model demonstrated a strain-recovery overshoot for cases programmed below T g and subjected to a constant mechanical load. This phenomenon was not observed for materials programmed above T g . Physical aging, in which the material was annealed for an extended period of time below T g , shifted the activation of strain recovery to higher temperatures and increased significantly the initial recovery rate. For fixed-strain recovery, the model showed a larger overshoot in the stress response for cases programmed below T g , which was consistent with previous experimental observations. Altogether, this work demonstrates how an understanding of the time-dependent behaviors of the glass transition can be used to tailor the temperature and deformation history of the shape-memory programming process to achieve more complex shape recovery pathways, faster recovery responses, and larger activation stresses.
104 citations