CRACKING PATTERNS IN METAL-CERAMIC LAMINATES - EFFECTS OF PLASTICITY

Multilayered metal-ceramic composites exhibit unique fracture characte ristics that result from the need to reinitiate cracks in adjacent cer amic layers across intact metal layers. Quantitative knowledge of the stress and strain fields around cracked brittle layers is required to predict the fracture modes of such composites. In this paper, two comp eting fracture modes are analysed for a laminate containing a precrack that spans several layers: fracture is either by co-planar crack grow th within the ceramic layers ahead of the initial crack, or, by multip le cracking within the ceramic layers. The appropriate boundary condit ions employed in the numerical modelling are determined by comparing f inite element predictions with experimental observations of elastic an d plastic strain distributions around single cracks in Al/Al2O3 lamina tes using moire interferometry. It is found that plastic yielding of t he metal layers encourages single, co-planar crack growth instead of m ultiple cracking. This competition between single and multiple crackin g is summarised in the form of a fracture map.