Mechanisms of Stress Relaxation and Failure in Metals Under Shock Compression

Abstract

Deformation behavior of materials at high strain rates is characterized by intensive nucleation and growth of defects both under shock wave compression and unloading conditions that may reduce to spall fracture in the bulk of sample. The influence of defects on the relaxation properties of the material shown in the elastic precursor decay, the self-similarity of plastic wave fronts, and the kinetics of spall fracture is developed. Experiments on the registration of the shock wave profiles by laser interferometry (VISAR) with high temporal resolution allow the studying of the kinetics of the elastic-plastic transition, due to the mechanism of structural relaxation in heavy accumulation of defects, plastic deformation, and spall fracture, and use the data to justify the wide-range constitutive equations reflecting the relationship between structural and traditional mechanical (stress, strain, strain rate) variables. Present work is concerned on the numerical simulation of the deformation behavior of vanadium under plate impact. The analysis of free surface velocity profiles allow us to estimate the values of the dynamic elastic limit and spall failure stress at strain rates in the range of 105–107 s−1. Decay of the elastic precursor and the formation of the spall fracture are discussed. A mathematical model explaining the exponential nature of the relaxation of the elastic precursor and spall fracture was proposed.