Abstract
The aim of the present study is to evaluate interfacial fracture toughness in model polyester/epoxy composite. This composite system was recently studied by Tandon and Pagano [1] in a push-out test. The progressive debonding portion of the load-displacement response including initiation of debonding, propagation and eventually catastrophic debonding of the remainder of the bonded interface were predicted using a single parameter characterized as the critical shear energy release rate of the interface. The model [1] predicted the apparent toughness of the interface to increase with the length of the debond while the numerical contribution of shear stresses to the potential energy release rate was found to be nearly constant.
In this work, we have used the end-notch flexure specimen (0.5 inch thick) consisting of polyester and epoxy rectangular beams with a non-adhesive insert on the interface (mid plane) as a starter crack, to evaluate the Mode II fracture toughness. A three point bending fixture with a total span of 4 inches is installed in a load frame and tested in a displacement control mode. The Mode II fracture energy is calculated from the load-deflection curve and crack extension data using compliance calibration method. The end-notch flexure specimen is also analyzed using the large radius axisymmetric damage model by Schoeppner and Pagano [2]. It has been shown that in the limit as the ratio of average cylinder radius R to laminate thickness T approaches infinity, the stress components and the governing equations of the large radius model are analytically equivalent to the flat laminate formulation. The crack-closure method is then used to calculate the potential energy release rate and the analytical predictions are compared with the experimental data.
