In-situ characterization of damage evolution in metal matrix composites

A composite's local response to initial damage under stress is the primary micromechanical process determining its fracture toughness, strength, and lifetime. Through the use of high energy X-ray microdiffraction, the elastic lattice strains of both phases in a Ti-SiC composite were revealed providing the in-situ load transfer under applied tensile stress at the scale of the microstructure. To understand the damage evolution, the measured strains were compared to those predicted by a modified shear lag model. Comparisons between the model and the data demonstrated the importance of accounting for the matrix axial and shear stiffness, provided an optimal stiffness ratio for load transfer and planar interpretation of the geometry in the composite, showed the matrix within and around the damage zone sustained axial load, and highlighted matrix yielding observed in the composite. It was also shown that an area detector is essential in such a study as it provides multiaxial strain data and helps eliminate the "graininess" problem.