Spherical impression of thin elastic films on elastic-plastic substrates

The mechanical behavior of thin elastic films deposited onto structural all oys plays a critical role in determining film durability. This paper presen ts analysis of an impression experiment designed to evaluate some of the re levant properties of these films. The modeling provides quantitative strain information which can be used to estimate the fracture toughness of the fi lm, the static friction coefficient of the surface and the constitutive beh avior of the substrate. Results are presented for radial and circumferentia l strain distributions in the film relevant to the interpretation of cracki ng patterns. Additionally, load-displacement curves are provided that may b e used to evaluate the plastic properties of the substrate. To facilitate e stimates of the film cracking strain through correlation with experiments, the radial strain distributions are presented as functions of impression de pth, yield strain and hardening exponent. (C) 1999 Elsevier Science Ltd. Al l rights reserved.