Weibull master curves and fracture toughness testing Part III Master curves for the evaluation of dynamic Charpy impact tests

Abstract

The existence of specimen-size-independent quasi-static Weibull master curves for macroscopically homogeneous solids characterizing strength and failure of both purely brittle materials and rather tough materials, which undergo an amount of stable crack growth prior to failure, has already been proved in earlier publications. In this paper, the concept of Weibull master curves is extended to the case of dynamic testing conditions, being typical for Charpy impact tests performed in the ductile-to-brittle transition temperature-range of ferritic-martensitic steels. Dynamic Weibull master curves can be constructed, if the stress-distributions, which are built up in the process zone of the specimens during the Charpy impact tests, can be described with a dynamic quasi-equilibrium approach. In this case, the dynamic Weibull master curves can be related to the quasi-static Weibull master curves with the help of the toughening exponent τ, characterizing the rate of toughness increase with increasing crack length. Characteristic magnitudes, being most convenient to estimate the capacity of the tested materials to undergo stable crack growth, microcracking and crack-tip shielding prior to rupture, can be derived as well from dynamic Weibull master curves as from quasi-static Weibull master curves.