Effect of Interface Crack and Corner Singularity in Bimaterial System – Experimental and Numerical Investigation

Pai, R N and M, Ramji (2012) Effect of Interface Crack and Corner Singularity in Bimaterial System – Experimental and Numerical Investigation. Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

It is of great importance to study behavior of adhesively bonded dissimilar materials as they are widely used in electronic packaging, plastic integrated circuit, welded joints of dissimilar materials, composite materials etc. Due to mechanical loading, cyclic variation in climate or changes in moisture content of ambience leads to high stress at corners or interface, where discontinuities of geometry or material property is present. In this study an attempt has been made to study the behavior of small crack at the interface of aluminum/epoxy bimaterial system. Initially stress intensity factors are estimated experimentally by digital photoelasticity and then compared numerically with a finite element model. Experimentally, ten-step phase shifting technique is used to get isochromatic phase map without ambiguity and later it is unwrapped to get the total fringe order over the model domain. Three fringe photoelasticity technique is also used to get total fringe order. From this information stress intensity factor at interface crack tip is determined using simplified multi-parameter stress field equation of Deng involving over-deterministic least square approach. Numerically stress intensity factors are evaluated by virtual crack closure integral method. Numerically J-integral method is also used for evaluating stress intensity factors for interface crack. We may have to account for the effect of material mismatch as well as temperatute effect at material interfaces. A bimaterial wedge corner can also act as a source for high stress concentration, and it’s singularity is different from crack tip. In the present work, analytically order of singularity is found out for the aluminium/epoxy bimaterial system and using this, stress fields around the corner is predicted. For finding the order of singularity modified stress field equations of Seweryn has been used with appropriate boundary conditions. A linear elastic fracture mechanics frame work is applied for the entire study.

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