Interlaminar fracture toughness testing of composite mode I and mode II DCB specimens

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Abstract
A computer controlled test procedure for evaluating mode I and mode II interlaminar fracture behavior was used in experiments with eight different resin matrix/graphite fiber composites. Four analytical methods for calculating fracture toughness were compared. These included an energy rate determination of theJ‐integral, a compliance calibration procedure, equations based on linear beam bending, and an Area method calculation. Methods that account for nonlinear material behavior, such as theJ‐integral, were needed for characterizing the systems with high fracture toughness. The ratio of mode II to mode I fracture toughness ranged from 1.5 to 8.0, depending on the material system. Finally, preliminary work with a technique for constant strain rate testing of mode I DCB specimens is presented.