THE CRACKED LAP SHEAR SPECIMEN REVISITED - A CLOSED-FORM SOLUTION

This paper revisits the cracked lap shear specimen and reports a close d form solution to determine three fracture parameters, the energy rel ease rate, the fracture mode mixity, and the fracture efficiency param eter. The solution is based on a beam-column approach pioneered by Gol and and Reissner. Because of the geometrically nonlinear nature of thi s specimen, it is found that the fracture parameters are functions of five independent nondimensional parameters. The closed form solution r eported in this paper provides a simple and useful tool to design the cracked lap shear specimen and to understand the behavior of this test geometry. The results in this paper suggest that to design a specimen with an energy release rate less dependent on the crack length, the a dherend thickness should be small compared to the specimen length, and the thicker or stiffer adherend should be used as the strap. For a sp ecimen of unequal adherend thickness, using the thicker adherend as th e strap would significantly reduce the likelihood of yielding in the a dherend. Compared with the finite element analyses found in the litera ture, the closed form solution shows good agreement in energy release rates, but less satisfactory agreement in Fracture mode mixities. Fina lly, the closed Form solution is used to give a reasonable explanation of anomalous debond behavior in a series of fatigue experiment using the cracked lap shear specimen.