FEM modeling of fiber/matrix debond growth in tension-tension cyclic loading of unidirectional composites

The fiber/matrix interface crack (debond) growth from fiber break in unidirectional composite subjected to high stress tension–tension cyclic loading is analyzed. The debond growth is simulated calculating the strain energy release rate GII by FEM in three-dimensional formulation and using power law with respect to the GII change to describe the debond growth rate. Two models were applied. In Model 1 the partially debonded fiber/matrix cylindrical unit with a fiber break is surrounded from all sides by an effective composite phase. In Model 2 the effective composite phase was used around the fiber/matrix unit except the region between the unit and the specimen surface, which contains neat matrix only. Calculations show that the average GII is slightly larger, when the analyzed fiber is closer to the specimen surface. The debond growth was simulated using interface fatigue parameters obtained from single fiber composite specimen tests in the literature. Simulation results show that debonds from fiber breaks close to the specimen surface grow faster than from fiber breaks inside the composite specimen.