DAMAGE DEVELOPMENT IN A SHORT-FIBER REINFORCED COMPOSITE

The important issue of finding a relationship between a macroscopic damage variable and the process of damage accumulation within a material is addressed in this article. Monotonic and cyclic deformation behavior has been studied in a randomly distributed glass reinforced polyester matrix composite. The composite material is called sheet molding compound, abbreviated as SMC, with a short glass fiber weight of 30%. The damage evolution in this planar isotropic material is studied by continuously monitoring axial, lateral, and specimen thickness strain components on the specimen. Based on these measurements, the damage volumetric strain was calculated that increased continuously with cycles in load-controlled experiments. However, in the strain-controlled experiments, where tensile stresses decayed rapidly with cycles, the corresponding damage volumetric strain reached a saturation level. Microscopic observations revealed that cracks grew along the matrix/fiber interfaces as well as the matrix/filler interfaces. Many of these cracks are normal to the specimen thickness direction. This observation is consistent with the increasing specimen thickness strain measured in the experiments.