DEVELOPMENT OF A DYNAMIC DECOHESION CRITERION FOR SUBSONIC FRACTURE OF THE INTERFACE BETWEEN 2 DISSIMILAR MATERIALS

We present findings of an experimental study of dynamic decohesion of bimaterial systems composed of constituents with a large material prop erty mismatch. Poly-methylmethacrylate (PMMA)-steel and PMMA-aluminium bimaterial fracture specimens were used. Dynamic one-point bend loadi ng was accomplished with a drop-weight tower device (for low and inter mediate loading rates) or a high-speed gas gun (for high loading rates ). High-speed interferometric measurements were made using the lateral shearing interferometer of coherent gradient sensing in conjunction w ith high-speed photography. Very high crack propagation speeds (termin al crack-tip speeds up to 1.5c(s)(PMMA), where c(s)(PMMA) is the shear wave speed of PMMA) and high accelerations (of about 10(7) g, where g is the acceleration of gravity) were observed and are reported. Issue s regarding data analysis of the high-speed interferograms are discuss ed. The effects of near-tip three-dimensionality are also analysed. Dy namic complex stress factor histories are obtained by fitting the expe rimental data to available asymptotic crack-tip fields. A dynamic crac k growth criterion for crack growth along bimaterial interfaces is pro posed. In the subsonic regime of crack growth it is seen that the open ing and shearing displacements behind the propagating crack tip remain constant and equal to their value at initiation, i.e. the crack retai ns a self-similar profile during crack growth at any speed. This forms the basis of the proposed dynamic interfacial fracture criterion.