Stress relaxation

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

An elastic-plastic stress analysis for a notched bar in plane strain bending

Abstract: An elastic-plastic stress analysis, which allows for linear work-hardening, has been carried out for a notched bar using the method of finite elements. Good agreement has been found with available experimental data and confirmation obtained of the idea that the strain at the notch surface is nearly constant over a large fraction of the root. However, some interesting differences exist between the present results and those apparently predicted from slip-line field theory. First, there is the surprising result that the maximum stress does not occur at the elastic-plastic interface. Secondly, in considering the stress intensification (the ratio, R , of the maximum stress to the yield stress), it is shown that slip-line field theory apparently over-estimates R at low loads but slightly under-estimates it near to general yield. The results for the stress intensification are used to re-analyse existing experimental data in order to find the temperature variation of the local fracture stress: this is found to be nearly constant over a range of 250°C.

Computational models for ductile and brittle fracture

Abstract: Computational models of dynamic ductile and brittle fracture are developed for wave propagation in one‐ and two‐dimensional geometries. The model features have been taken mainly from detailed observations of samples partially fractured during impacts, but the functional forms are consistent with theoretical results where applicable. Basic features of the models are the nucleation and growth (hence, the acronym NAG for the models) of voids or cracks, and the stress relaxation resulting from the growing damage. The results of the calculations include number and sizes of cracks, voids, or fragments as a function of position in the material. The NAG analysis presents the nucleation law, determined from experiment, and two growth laws: both growth and nucleation are functions of stress and stress duration. Procedures for treating cracks with a range of sizes and orientation are presented with the method for computing the stress relaxation that accompanies growth of damage. Brittle fracture is essentially aniso...

Yield stress: A time-dependent property and how to measure it

Abstract: This paper reviews the different aspects of the yield stress phenomenon and attempts a synthesis of knowledge. Yield stress can be probed using constant shear stress or shear rate. The magnitude of the result depends on the time allowed to determine whether the sample has developed continuous flow or has ceased flowing. It is closely associated with creep, stress growth and thixotropic breakdown and recovery, and the characteristic times of these transient responses play a part in yield stress measurement. In thixotropic fluids, yield stress is a function of structure and hence of time. In simple thixotropy, the yield stress derived from the equilibrium flow curve is the same as that for the fully built-up structure. But in many materials, the static yield stress obtained after prolonged rest is much higher than the dynamic yield stress from the equilibrium flow curve. This is associated with the phenomenon in which the equilibrium flow curve bends upwards as the shear rate is reduced to very low values. The paper also reviews the many methods that can be used to measure yield stress. It is pointed out that the choice of observation time or shear rate to use should be related to the characteristic time of the flow process to which the result is to be applied. Examples discussed are solids suspension capability of fluids, levelling and sagging, pipeline flow and start-up power requirement of mixers.