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 loading is analyzed numerically. The material on each side of the bond line is characterized 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 creation of new free surface. The resistance to crack initiation and the crack speed history are predicted without invoking any additional failure criterion. Full finite strain transient analyses are carried out. A plane strain model of the configuration used in experiments of Rosakis and co-workers is analyzed. Calculations are carried out for parameters characterizing a steel-PMMA bimaterial. For a sufficiently low impact velocity, the crack speed increases smoothly to the PMMA Rayleigh wave speed, whereas above a sharply defined transition impact velocity, the crack speed reaches a value somewhat less than the PMMA dilational wave speed. This high speed crack growth is associated with multiple crack face contact, separated by discrete micro-crack like openings behind the main shear crack. The calculations reproduce, at least qualitatively, the type of crack speed histories and crack tip fields seen in the experiments. They are also consistent with optical observations of finite multi-site contact occurring at intersonic crack speeds. (C) 1999 Elsevier Science Ltd. All rights reserved.