Mixed-mode delamination of multidirectional composite laminates at 0°/θ° ply interfaces

The objective of this study is to determine the mixed-mode I+II interlaminar fracture toughness at high mode I content for a 0°/45° ply interface. Mixed-mode I+II delamination tests on unidirectional and multidirectional specimens were performed using ADCB and AMMF methods. The procedure used for choosing the stacking sequence resulted in desirable propagation behaviors of the delamination. There was no change of delamination plane, an acceptable crack front profile, no initial specimen curvature, and no energy dissipation through global specimen damage. For data reduction, the experimental compliance method was the most consistent in determining the total energy release rate. Finite element simulation proved to be an indispensable analysis tool. A resin-rich interlayer was modeled at the delamination interface to eliminate the non-convergence behavior of the energy release rate. For delamination between plies of different orientations, the mode decomposition could only be analyzed by the finite element method. The ADCB configuration offered a very high mode I content (90-95%) while the AMMF offered a moderately high mode I (70-78%)