VOID GROWTH AND COALESCENCE IN CONSTRAINED SILVER INTERLAYERS

The mechanisms of void growth and coalescence during fracture of thin Ag interlayers were studied by tensile testing and metallographic examination. No measurable void growth was observed in the deformed interlayers prior to fracture. The fracture surface dimple size, however, increased with increasing interlayer diameter-to-thickness ratio (D/T). The experimental results suggest that fracture in the constrained Ag interlayers occurred by void initiation at silicon oxide inclusions followed immediately by void coalescence. The highly triaxial stress state in the interlayer promoted void coalescence by plastic instability and accounts for the observed change in fracture surface dimple size with D/T. An expression, based upon a slip-line field model of the deformation zone between neighboring voids, is presented which relates the dimple size to the average inclusion diameter and the stress state in the interlayer. The predictions of the expression are in broad agreement with the experimental data.