A modified test for measuring the interlaminar tensile strength of fiber-reinforced ceramic composites

The low interlaminar tensile (ILT) strength of ceramic composites with two-dimensional fiber architectures presents serious challenges in the design of thermostructural components. Existing protocols for measuring ILT strength remain contentious because of the presence of free edges. The principal objective of the present study is to introduce a modified test that eliminates machined edges (and associated flaws) from the volume that experiences stress, thereby enabling an ILT measurement more representative of the delamination response expected in actual components. A secondary objective is to assess the efficacy of a layer-to-layer interlock weave relative to a satin weave in the ILT strength of SiC/SiC composites. These goals are addressed by exploring oversized circular specimens. Experiments and numerical analyses of both the oversized and the standard configurations are used to characterize the stress distributions and the failure conditions. The numerical results indicate that stress concentrations arise from thermal expansion mismatch in the near-edge regions of the standard configuration and exacerbate the deleterious effects of machining flaws. The ILT strengths of the oversized specimens are significantly higher than those of the standard configuration (by 30–50%), consistent with the exclusion of machining flaws and the reduced stress concentration. Moreover, the strength of the composite with the interlock weave is about 50% greater than that for the satin weave.