Showing papers by "Amol A. Gokhale published in 2023"

Surface hardening through oxygen diffusion in niobium: The defining role of stress inhomogeneity in tensile embrittlement

Abstract: Surface hardening, through oxygen diffusion, enforced significant tensile embrittlement of a commercial niobium (Nb) alloy (C-103). This was explored with microscopic digital image correlation and crystal plasticity finite element (CPFE) modeling. In particular, the presence of an oxygen-rich surface layer provided a gradient in hardness and elastic stiffness. These coincided with an increase in yield and tensile strength but a significant drop in ductility. The latter was reflected in the strain localization(s) and crack(s) on the hard gauge region, which ultimately led to a brittle failure. Full-field CPFE simulations were conducted on the actual microstructures. Our model, without crack and damage initiation, predicted extreme stress inhomogeneity during the tensile deformation. In brief, ∼5 times higher stress concentration was noted in the oxygen-rich hard surface grains. This appeared to be responsible for the subsequent crack initiation and embrittlement.

Investigation of shock transmission and amplification/mitigation in aluminium foams

Abstract: The present work investigates factors which control the stress generated at the back face of end wall-mounted shock-loaded aluminum foam. When the applied shock pressure is higher than the plastic strength of the foam, the foam deforms plastically generating a compaction wave traveling below shock velocity. Wave reflection and momentum transfer at the end wall result in shock amplification. With increasing foam length, the stress at the end wall decreases, finally leading to shock mitigation. A relation between compaction wave characteristics, foam densification, and stress generated at the end wall is established.