The effect of bond strength and loading rate on the conditions governing the attainment of intersonic crack growth along interfaces

Dynamic crack growth along a bimaterial interface under impact shear loadin g is analyzed numerically. The material on each side of the bond line is ch aracterized by an isotropic hyperelastic constitutive relation. A cohesive surface constitutive relation is also specified that relates the tractions and displacement jumps across the bond line and that allows for the creatio n of new free surface. The resistance to crack initiation and the crack spe ed history are predicted without invoking any additional failure criterion. Full finite strain transient analyses are carried out. A plane strain mode l of the configuration used in experiments of Rosakis and co-workers is ana lyzed. Calculations are carried out for parameters characterizing a steel-P MMA bimaterial. For a sufficiently low impact velocity, the crack speed inc reases smoothly to the PMMA Rayleigh wave speed, whereas above a sharply de fined transition impact velocity, the crack speed reaches a value somewhat less than the PMMA dilational wave speed. This high speed crack growth is a ssociated with multiple crack face contact, separated by discrete micro-cra ck like openings behind the main shear crack. The calculations reproduce, a t least qualitatively, the type of crack speed histories and crack tip fiel ds seen in the experiments. They are also consistent with optical observati ons of finite multi-site contact occurring at intersonic crack speeds. (C) 1999 Elsevier Science Ltd. All rights reserved.