Cohesive zone modeling of crack nucleation at bimaterial corners

The prediction of crack nucleation from bimaterial corners that have the sa me corner angle land therefore singularity) via stress intensity factors is fairly well established. The objective of this work was to examine crack n ucleation from a range of corner angles and see if a more general crack nuc leation criterion could be formulated, A series of experiments was conducte d using an aluminum-epoxy bimaterial specimen loaded under 4-point bending, In addition to the usual measurements of load and an associated displaceme nt, the displacements near the corner were measured using moire interferome try, Numerical analyses were first conducted assuming a rigid interface. Ho wever, the resulting displacements differed from the measured ones, especia lly near the corner and along the interface. The interface was then modeled as a separate constitutive entity by incorporating a cohesive zone model i n the numerical analysis. Following calibration via an interface crack conf iguration (zero corner angle), the cohesive zone model yielded displacement s that were in good agreement with the measured values for all the other co rner angles that were considered. The predicted failure loads were also in good agreement with the experimental results. Thus the consistent nucleatio n criterion was that the area under the traction-separation curve and its m aximum traction (the dominant cohesive zone model parameters) remain the sa me. The numerical solutions indicated that the plastic deformation in the e poxy was small and that failure was predominantly in opening mode. In addit ion, the critical vectorial crack opening displacement and mode-mix were in dependent of the corner angle. Finally, a simple design parameter was propo sed for predicting the failure load of a bimaterial specimen with an arbitr ary corner angle, based on the failure load of a bimaterial specimen with a n interface crack. (C) 2000 Elsevier Science Ltd. All rights reserved.