Elastic and elastoplastic response of thin copper foil

Abstract

The tensile elastic, elastoplastic and low strain plastic parameters of the 12–35 μm thick rolled (R) and electrodeposited (ED) copper foils have been characterized between 296 and 573 K and after an anneal exposure at up to 1173 K. At 296 K, all parameters are inversely proportional to grain size but the thermal effects dominate at the higher temperatures. For the R foils, the temperature coefficient of elastic modulus (E) is more or less identical to that for the bulk copper. For the ED foils, the coefficient increases with decreasing grain size; this effect is presumably related to the characteristic point defect structure generated during deposition. A significant grain growth ensues upon annealing but the post-anneal grain size has little effect on E; for the R foil, however, E decreases sharply with the anneal induced emergence of new crystallogrpahic textures with orientations near (100). The tangent modulus (E t) in the elastoplastic regime decreases with strain and with temperature, a very large drop in E t with anneal temperature suggests that both the diminution of dislocation activity and the texture modification are the contributory factors. It is argued that the strain hardening parameter (n) in the elastoplastic regime, and the strain rate hardening parameter (m) and the flow stress in the low strain plastic regime influence the handling damage to the thin foil.