Microstructure Based Failure Criterion For Ductile Materials

Abstract

For ductile metals, the process of dynamic fracture occurs through nucleation, growth and coalescence of voids. The stress required to nucleate these voids is inferred from the velocimetry data (using the acoustic approach) and termed as the spall strength. This is a key parameter that is used to evaluate a material’s susceptibility to damage and failure. However, it is also well recognized that the dynamic parameters used to generate the shock state such as pulse duration, tensile strain-rate and peak stress coupled with material microstructure itself affect the material response in a complex manner. Yet, it is impossible to capture all this information by assessing only the spall strength measured from simple one-dimensional Photon Doppler Velocimetry measurements. Although, there exist widely used corrections proposed by Kanel et. al. that allow for the inclusion of some of these complexities into the measured spall strength but still does not take the microstructure into account. In this work, we propose another scheme for normalization of spall strength with a damage area to capture the complexities included in the damage and failure process especially pertaining to microstructure. We will also demonstrate the application of this scheme by applying to examples of materials such as Copper, Copper-24 wt%Ag, Copper-15 wt% Nb and additively manufactured 316L SS.

Mechanism of Microscopic Fracture of Typical Shell Steel under Impact Loading

“…Zerilli and Armstrong [26] developed an intrinsic structural model that takes into account the influence of the material microstructure. Bourne et al [27][28][29] and others have carried out a number of studies to analyze the influence of the material crystal structure on the fracture behavior and proposed a method to calculate the fracture strength based on the number of microscopic defects, such as dislocations and holes in the material. ey concluded that there was a correlation between the number of microscopic defects and the grain size of the material.…”