Abstract
Abstract : Numerical simulation and experiments on the toughness and fatigue crack growth resistance of MEMS relevant thin film structures are reported. Structures consisting of metal films (aluminum, 0.1 to 2.0 micrometers thickness) confined between elastic substrates (semiconductor wafers) are considered. The study is concerned with the influence of the thickness of the metal film on the fatigue failure response. Numerical simulations of fatigue crack growth are conducted by use of cohesive zone models. Both a damage mechanics-based model as well as a model based on dislocation mechanics are employed. To enable these computations, a strain gradient plasticity model is developed. It is demonstrated that cohesive zone models of fatigue enable analysis of fatigue failure to cases where the Paris Law is no longer applicable. The influence of geometric constraint (thin film confinement, presence of interfaces), mechanical constrain (T-stress), size, and strain gradients on fatigue crack growth are demonstrated.
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