Experimental investigation of interfacial fracture parameters and crack initiation under mechanical and thermomechanical loading

Mechanically, and thermomechanically stressed interface cracks in adhesivel y bonded bimaterials (PMMA-aluminum) with a large elastic and thermal prope rty mismatch are experimentally studied The elasto-optic effects are mapped as (sigma(x) + sigma(y)) contours in the PMAA halves and interfacial fract ure parameters are estimated. Crack initiation under mechanical and thermom echanical loading conditions are shown to be controlled by different microm echanical processes. The results suggest that the micromechanical unlocking of microcavities and microprotrusions along the interface is primarily res ponsible for failure initiation under thermomechanical loading conditions. This is unlike the mechanical loading situations wherein fracture toughness is derived primarily from the breakage of interlocking microentanglements. The measured values of the fracture parameter Delta Im(Ka(i epsilon))(T) d ue to a temperature rise is a constant and much higher than its real counte rpart (Delta psi(T)(a) approximate to 76 - 82 degrees). The Delta(Ka(i epsi lon))(T)\(cr) thus obtained are much lower than the mechanical counterparts .