, Volume 15, Issue 3, pp 277-291
Date: 19 Jan 2011

Plastic deformation in multilayered thin films during indentation unloading: a modeling analysis incorporating viscoplastic response

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The indentation behavior of metal/ceramic multilayered thin films is studied numerically using the finite element method. The axisymmetric model consists of alternating aluminum (Al) and silicon carbide (SiC) layers above a silicon (Si) substrate, with the rate-dependent viscoplastic response of Al accounted for. Different unloading rates, with and without a hold period at the peak indentation load, are considered. Attention is devoted to plastic deformation in the Al layers during the unloading phase of indentation. It is found that the hold period stabilizes the deformation so the unloading response becomes insensitive to the unloading rate. However, significant parts of the Al layers under indentation still experience plastic deformation during unloading, due to the mechanical constraint imposed by the hard SiC layers. Consequently unloading is no longer an elastic event in this heterogeneous material system. The unloading induced plasticity is further analyzed by tracking the stress and strain histories inside the material throughout the course of indentation.