Spherical impression of thin elastic films on elastic–plastic substrates

The mechanical behavior of thin elastic films deposited onto structural alloys plays a critical role in determining film durability. This paper presents analysis of an impression experiment designed to evaluate some of the relevant properties of these films. The modeling provides quantitative strain information which can be used to estimate the fracture toughness of the film, the static friction coefficient of the surface and the constitutive behavior of the substrate. Results are presented for radial and circumferential strain distributions in the film relevant to the interpretation of cracking patterns. Additionally, load-displacement curves are provided that may be used to evaluate the plastic properties of the substrate. To facilitate estimates of the film cracking strain through correlation with experiments, the radial strain distributions are presented as functions of impression depth, yield strain and hardening exponent.