S.T. Tu

Residual stress analysis in the film/substrate system with the effect of creep deformation

The physical phenomenon of residual stress relaxation and redistribution in the film/substrate systems due to creep deformation is focused in this work. A new analysis model to elucidate either the film or the substrate subjected to creeping deformation is developed. Specific analyses are made on the NiCrAlY coating-based system and silicon-epoxy bilayer structure. Results reveal that the proposed model can lead to an excellent agreement with the simulated results of finite element method. Furthermore, comparisons among FE results, the present model, and Zhang’s creep solution [J. Appl. Phys. 101, 083530 (2007)] have been carried out. Meanwhile, comparisons between Hsueh’s viscoelastic solution [J. Appl. Phys. 91, 2760 (2002)] and our current model in the case of creep exponent n=1 have also been conducted. Effects of thickness ratio of the film to the substrate on the stress distribution and the evolution of the accumulated creep strain have also been discussed in this paper.

Analysis on multiple cracking in film/substrate systems with residual stresses

The multiple cracks might be initiated in the film on a substrate due to the presence of residual stress. In this paper, the multiple film cracking in the film/substrate systems with residual stress was analyzed. First, a relatively simplified model with the closed solutions considering the edge effect was developed to predict the residual stress within the film segment. Some obvious relationships between the material properties and the dimensions of the film and substrate and the stress distribution in the film could be reflected by using this model. By comparing the analytical results with those from the existing analytical models, finite element analysis, and the existing experimental measurements, it could be concluded that the present analytical model was very rigorous. Then, the energy criterion was adopted to perform the analysis on multiple film cracking on the basis of the knowledge on the residual stress distributions. The closed-form solution for the critical misfit strain for the crack initiat...

Multiple film cracking in film/substrate systems with mismatch strain and applied strain

Multiple cracking of brittle films deposited on the relatively soft substrate was commonly used in different applications. In the present paper, multiple film cracking in the film/substrate systems was analyzed. The system was subjected to the combination of the residual stresses due to the mismatch strain between the film and substrate and the applied stress due to the unidirectional strain on the substrate. First, a simply analytical model was developed to derive the closed-form solutions for the residual stress distribution and redistribution due to the edge effects in the film segment. Second, the energy and strength criteria were adopted to perform the analysis on the multiple film cracking on the basis of the knowledge on the residual stress distributions. Third, the case of SiOx film/polyethylene terephthalate substrate system was used to illustrate the implementation of this model. The relationship between the fracture energy as well as the film strength and the film thickness was obtained. The pr...