Mechanical properties at high strain rates

Abstract

In the range of high strain rates, the mechanical behaviour of materials is characterized by an increased strain rate sensitivity, by increasing effects of mass inertia forces and by the adiabatic character of the deformation process. For the relation between stress, strain and strain rate, empirical formulae are now mostly replaced by material laws based on structural mechanical models, whose parameters are to be determined by adequate systematic methods. Also special effects such as the influence of strain rate on the strain at the lower yield point of bcc-metals can be quantitatively described by simple models. The fracture mode and ductility are highly affected by the strain rate. The elongation at fracture can be increased due to the stabilising effect of the strain rate sensitivity similar to the super plastic behaviour. On the other hand, it can be reduced by the thermal induced instability, by the increasing sensitivity for internal notches and by the multiaxial stress state caused by inertia forces. The strain rate affects also the ductile fracture conditions as well as the transition temperature to clearage fracture.

Characterization, modelling and simulation of deformation and fracture behaviour of the light-weight wrought alloys under high strain rate loading

“…T m , T 0 , and T are the absolute melting point, room temperature, and actual temperature, respectively. b is a material constant which can be set to 3 for several materials [6]. Assuming that the major part of deformation energy is transferred to heat during the dynamic deformation process and that the remaining part is consumed by an internal energy increase, e.g.…”

“…The parameter s h signifies the stress extrapolated from the range of high strain rates down to _ ¼ 0 s À1 ; Z is the damping parameter. The influence of the temperature on the flow stress can be considered by a multiplicative function [5], so that the material behaviour can be described by [6] s…”

Estimating the Strain-Rate-Dependent Parameters of the Cowper-Symonds and Johnson-Cook Material Models using Taguchi Arrays

“…Investigations of this effect have been performed by many researchers over the last century, like Hopkinson, Charpy, Taylor [1], Zerilli, Armstrong, Johnson [2], [3], etc. In the last 20 years, strain rate influence on material behaviour is still interesting for researchers like El-Magd [4], Zhao and Gary [5], Huh et al [6] to [8], etc.…”

Dynamic compressive flow behaviour of S15C low carbon steel over wide temperature range

“…The activation energy can be determined experimentally by the following expression 30,31 DG 1~{ Tn 1 (Ls=LT): e (9) where n* is the activation volume obtained from equation (8). The activation energy of S15C, as obtained from equation (9), can be plotted as a function of flow stress and compared with the data reported by ElMagd, 32 as shown in Fig. 9.…”