Rate Effects in Mode - II Fracture of Plastically Deforming , Adhesively - Bonded Structures

Results from a combined experimental and numerical investigation into the effects of rate on mode-II fracture of a plastically-deforming, adhesively-bonded joint are presented. It is shown that a cohesive-zone model has to be modified to include coupling between normal and shear modes of deformation when there is extensive shear deformation of the adhesive layer. A suitable cohesive-zone modeling strategy is described, and the mode-II cohesive parameters determined from the model are presented as a function of loading rate. Previous studies of the same system showed that the effects of rate in mode-I were limited to the probability that a crack growing in a toughened quasi-static mode would spontaneously make a transition to a brittle mode of fracture. No such transitions were found for mode-II fracture. Crack growth always occurred in a quasi-static fashion. While there was some evidence that rate might affect the mode-II fracture parameters, these effects were very limited even up to crack velocities of about 1000 mm/s. Any possible effects was limited to a very minor increase in toughness and strength with increased loading rates. However. the magnitude of these possible increases were comparable to the magnitude of the uncertainties in the measured values.