HIGHLY TRANSIENT ELASTODYNAMIC CRACK-GROWTH IN A BIMATERIAL INTERFACE - HIGHER-ORDER ASYMPTOTIC ANALYSIS AND OPTICAL EXPERIMENTS

A HIGHER ORDER asymptotic analysis of the transient deformation field surrounding the tip of a crack running dynamically along a bimaterial interface is presented. An asymptotic methodology is used to reduce the problem to one of the Riemann-Hilbert type. Its solution furnishes displacement potentials which are used to evaluate explicitly the near-tip transient stress field. Crack-tip fields corresponding to crack speeds up to the lower of the two shear wave speeds are investigated. An experimental study of dynamic crack growth in PMMA-steel interfaces using the optical method of CGS and high speed photography, is also described. Transonic terminal speeds (up to 1.4c(5)(PMMA)) and initial accelerations (similar to 10(8) ms(-2)) are reported and discussed. Transient effects are found to be severe and more important than in homogeneous dynamic fracture. For subsonic crack growth, these experiments are used to demonstrate the necessity of employing a fully transient expression in the analysis of optical data to predict accurately the complex dynamic stress intensity factor history.