Microscale damage evolution and stress redistribution in Ti-SiC fiber composites

Local damage evolution in a composite is the primary micromechanical process determining its fracture toughness, strength, and lifetime. In this study, high energy X-ray microdiffraction was used to measure the lattice strains of both phases in a Ti-SiC fiber composite laminate. The data provided in situ load transfer information under applied tensile stress at the scale of the microstructure. To better understand damage evolution, predictions of a modified shear lag model were compared to the strain data. This comparison (1) demonstrated the importance of accounting for the matrix axial and shear stiffness, (2) optimized the stiffness ratio for load transfer, and (3) improved the interpretation of the ideal planar geometry commonly used in micromechanical composite models. In addition, the results proved the matrix within and around the damage zone sustained substantial axial load and locally yielded. It was also shown that an area detector is essential in such a diffraction study as it provides multi-axial strain data and helps eliminate the "graininess" problem.