Stress relaxation

About: Stress relaxation is a research topic. Over the lifetime, 12959 publications have been published within this topic receiving 270815 citations.

Tensile stress evolution during deposition of Volmer–Weber thin films

Abstract: A simple model is presented that predicts the kinetics of tensile stress evolution during the deposition of thin films that grow by the Volmer–Weber mechanism. The generation of a tensile stress was attributed to the impingement and coalescence of growing islands, while concurrent stress relaxation was assumed to occur via a microstructure-dependent diffusive mechanism. To model the process of island coalescence, finite element methods were employed and yielded average tensile stresses more consistent with experimental observations than those predicted using previously reported analytical models. A computer simulation was developed that models the process of film growth as the continuous nucleation of isolated islands, which grow at a constant rate to impinge and coalesce to form a continuous polycrystalline film. By incorporating the finite element results for stress generation and a microstructure-dependent stress relaxationmodel, the simulation qualitatively reproduced the complex temperature-dependent trends observed from in situ measurements of stress evolution during the deposition of Ag thin films. The agreement includes simulation of the decreasingstress relaxation rate observed during deposition at increasing temperatures.

Residual stress relaxation in an AISI 4140 steel due to quasistatic and cyclic loading at higher temperatures

Abstract: Residual stresses can be relaxed by supplying sufficiently high amounts of thermal and/or mechanical energy, which converts the residual elastic strains to microplastic strains. In order to better understand this relaxation behavior, shot peening induced residual stresses in normalized condition and in quenched and tempered condition of the steel AISI 4140 (German grade 42 CrMo 4) were investigated in annealing experiments, quasistatic loading experiments and bending fatigue experiments at 25, 250 and 400°C. The residual stress relaxation during alternating bending occurs in different regimes. First, thermal relaxation reduces the residual stresses during specimen heating. The relaxation during the first cycle can be discussed on the basis of the effects due to quasistatic loading, if the inhomogeneous distribution of the loading stress is taken into account. Differences in the behavior after the two heat treatments result from the Bauschinger-effect and effects of dynamic strain ageing. Owing to cyclic creep effects, the interval between the first cycle (N=1) and the number of cycles to crack initiation Ni is characterized by residual stresses which decrease linearly with the logarithm of N. Finally for N>Ni the reduction of residual stresses with the logarithm of N is stronger than linear.

Large Step Shear Strain Experiments with Parallel‐Disk Rotational Rheometers

Abstract: A new method is proposed and tested for step shear strain experiments with parallel‐disk rotational rheometers. The method is applicable to large strains, i.e., outside the linear viscoelastic region. The nonhomogeneity of the strain in the parallel‐disk rheometer is accounted for by a correction term which is similar to the well‐known Rabinowitsch correction in capillary rheometry. The transient shear relaxation moduli of a low‐density polyethylene (150°C) and of a polystyrene (180°C) from this method agree very well with equivalent data from a cone‐and‐plate rheometer. The two different geometries give an overlapping set of data; small‐strain data (γ=0.1−5) from cone‐and‐plate and large‐strain data (γ=0.4−25) from parallel disk. The step strain data support the separability of the relaxation modulus into time‐ and strain‐dependent functions. The strain dependence is well approximated by a sigmoidal function. The data were obtained with a Rheometrics dynamic spectrometer having a maximum angular displace...

Application of nonlinear viscoelastic models to describe ligament behavior

Abstract: Recent experiments in rat medial collateral ligament revealed that the rate of stress relaxation is strain dependent and the rate of creep is stress dependent. This nonlinear behavior requires a more general description than the separable quasilinear viscoelasticity theory commonly used in tissue biomechanics. The purpose of this study was to determine whether the nonlinear theory of Schapery or the modified superposition method could adequately model the strain-dependent stress-relaxation behavior of ligaments. It is shown herein that both theories describe available nonlinear experimental ligament data well and hence can account for both elastic and viscous nonlinearities. However, modified superposition allows for a more direct interpretation of the relationship between model parameters and physical behavior, such as elastic and viscous nonlinearities, than does Schapery's theory. Hence, the modified superposition model is suggested to describe ligament data demonstrating both elastic nonlinearity and strain-dependent relaxation rate behavior. The behavior of the modified superposition model under a sinusoidal strain history is also examined. The model predicts that both elastic and viscous behaviors are dependent on strain amplitude and frequency.