Mechanical behavior and damage development of unidirectional brittle matrix composites

Development of several damage mechanisms, including matrix cracking, interface debonding/sliding and fiber fractures in a brittle matrix composite are observed in several experiments including tensile testing under the microscope, acoustic emission monitoring of monotonic and loading-unloading tensile testing. Damage mechanisms and their development are identified and correlated with the macroscopic deformation. Tensile tests at elevated temperature are also conducted to study the effect of interphase and initial stresses on the mechanical behavior of the composite. The matrix cracking stress is found to be sensitive to the interphase and can be affected by moderate temperature change. The interpretation is made possible by theoretical efforts to model the macroscopic mechanical behavior in terms of microscopic damage and deformation. A cylinder model based on the principle of virtual work is derived, and macroscopic deformation correlated with the microscopic damage and deformation. A more general approach based on first principles of elasticity successfully derives the same results as the ones derived from the cylinder model. The results are used to help identify microscopic damage development through interpretation of macroscopic deformation. Although the work was focused on the mechanical behavior and damage development of a specific ceramic composite (Silicon Carbide fiber reinforced Cathium Aluminosilicate), the results from the cylinder model and especially from the general damage model are not limited to the particular material.