Enhanced and weakened strength in brittle film-substrate structure

Abstract

The mechanical properties of multi-use multilayers including the apparent tensile strength are important for estimating the multilayer's reliability. Yet in biaxial flexure, there exist enhanced or weakened performances when measuring apparent strength of laminates, resembling those found in uniaxial tensile load. In this paper, a model is proposed to predict the effect of thin film on apparent strength in terms of the applied tensile load. Six cases are discussed to characterize the enhanced or weakened performances of laminated membranes by introducing Apparent Strength Enhancement Factor (ASEF). It is notable that the ASEF is independent from thermal residual stresses in the case where substrate can continue to sustain the entire external load solely when film cracks first. Experimental results show clearly that fracture stress of laminated half-cell is lower than that of corresponding anode substrate. The prediction capability of the proposed model has been validated by the experimental results, though additional experiments are still required in order to critically assess the model's predictions over a range of bilayer laminates. In addition, comparison of the reverse mechanical performances between different types of loading reveals that the present analysis is significative for design and discussion of the mechanical integrity for multi-use multilayers.