Mode II cohesive law extrapolation procedure of composite bonded joints

A novel extrapolation procedure to predict the mode II cohesive laws of adhesive joints is presented. At first, a recently proposed compliance based experimental method to extract mode II Cohesive Laws is extended to the eccentric end-notched flexure test EENF and generalized including the effect of the bond line thickness and to this end, improved expressions for the compliance, J-Integral and shear displacement at the crack tip are derived. Assuming that every effect associated to the damage is included in the equivalent crack length, new expressions related to the Compliance (C-0), JIntegral (J(0)) and crack tip shear displacement (Delta(0)) are defined and invariant relations between J(0)-Delta(0) and Delta(0)- C-0 are elicited for a given material system and test configuration. Finally, an extrapolation procedure is presented, based on the J(0)-Delta(0) and Delta(0)- C-0 calibrated curves, which enables to estimate the cohesive laws for a wide range of adhesive to adherend ratio of a given material system by processing only the load -displacement curve.