Shear Strength as a Function of Test Rate for SiCf/BSAS Ceramic Matrix Composite at Elevated Temperature

Abstract

Both interlaminar and in‐plane shear strengths of a unidirectional Hi‐Nicalon™‐fiber‐reinforced barium strontium aluminosilicate (SiCf/BSAS) composite were determined at 1100°C in air as a function of test rate using double‐notch shear test specimens. The composite exhibited a significant effect of test rate on shear strength, regardless of orientation. The shear strength degraded by about 50% as the test rate decreased from 3.3 × 10−1 to 3.3 × 10−5 mm/s. The rate dependency of shear strength was similar to that observed for ultimate tensile strength at 1100°C for the two‐dimensional (2‐D) SiCf/BSAS composite, in which tensile strength decreased by about 60% when the test rate varied from 5 to 0.005 MPa/s. A phenomenological, power‐law slow crack growth model is proposed and formulated to account for the rate dependency of shear strength of the composite. The proposed model has been validated with additional results of both constant stress‐rate and constant stress testing in shear at 1100°C using a 2‐D Nicalon‐fiber‐reinforced crossply magnesium aluminosilicate (SiCf/MAS‐5) ceramic matrix composite.