Stress relaxation

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

Residual stresses in DLC/Si and Au/Si systems: Application of a stress-relaxation model to the nanoindentation technique

Abstract: Residual stress in a thin film was analyzed by the nanoindentation technique. Two dominant effects of residual stress to indentation were summarized as the slope change in loading curve and the invariant value of intrinsic hardness. A stress-sensitive reversibly deformed zone around contact was modeled to explain the indentation behaviors under a residually stressed state. Finally, the residual stress was evaluated from the changes in contact shape and applied load during stress relaxation under the condition of constant indentation depth. The residual stresses in diamond-like carbon and Au films analyzed from this model agreed well with the average values measured by the curvature method.

Dynamic Strain Aging and the Wire Drawing of Low Carbon Steel Rods

Abstract: The dynamic strain aging behaviour of low carbon steel wire rod was examined at room temperature to 450°C using tensile testing at strain rates of 10-4 to 10-1 s-1 The effects of temperature and strain rate on the yield stress, flow stress, UTS, fracture stress, and fracture strain were investigated in detail. In agreement with previous studies, work hardening peaks, minima in ductility, and negative strain rate dependences of the flow stress were observed between 100 and 400°C, the positions of which depended on the strain rate. A model for dynamic strain aging is employed to predict whether or not it will occur at the strain rates and temperatures involved in commercial wire drawing. For a steel containing 32 ppm N, a temperature higher than about 315°C must be attained for dynamic strain aging to occur; this is higher than the temperatures usually encountered in drawing. However, the model also predicts that if the N content is increased to 115 ppm, the minimum temperature for dynamic strain aging decreases to about 250°C, which can be attained if the die and capstan cooling are not adequate. The negative rate dependence of the flow stress attributable to dynamic strain aging is considered to promote flow localization and, therefore, to be a possible cause of wire breaks during drawing.

Stress and wafer bending of a-plane GaN layers on r-plane sapphire substrates

Abstract: The stress and wafer bending of (11 2- 0) a -plane GaN layers of different thicknesses grown on (1 1- 02) r -plane sapphire substrates by hydride vapor phase epitaxy were studied by high-resolution x-ray diffraction and photoluminescence and photoreflectance spectroscopies. The layers are found to be under compression in the growth plane and under tension in the growth direction. The elastic and thermal anisotropies of the GaN and the sapphire crystal result in an in-plane stress and a wafer curvature, both of which are different in the two in-plane directions parallel and perpendicular to the GaN c axis. The GaN unit cell is no longer hexagonal but orthorhombic. The stress relaxes with increasing GaN layer thickness while the curvature of the wafer increases. Different stress relief mechanisms are considered, and the stresses in the layer and the curvature of the wafer are calculated using standard models on wafer bending. The results suggest that the wafer bending is the dominant stress relief mechanism. In addition, the redshift of the near-band-edge photoluminescence and the free exciton photoreflectance peaks with increasing layer thickness is correlated with the strain data determined by x-ray diffraction. © 2006 American Institute of Physics.

Cooling rate and stress relaxation in silica melts and glasses via microsecond molecular dynamics.

Abstract: We have conducted extremely long molecular dynamics simulations of glasses to microsecond times, which close the gap between experimental and atomistic simulation time scales by two to three orders of magnitude. Static, thermal, and structural properties of silica glass are reported for glass cooling rates down to 5×10(9) K/s and viscoelastic response in silica melts and glasses are studied over nine decades of time. We present results from relaxation of hydrostatic compressive stress in silica and show that time-temperature superposition holds in these systems for temperatures from 3500 to 1000 K.