Thermal Shock Damage in a Two‐Dimensional Woven‐Fiber‐Reinforced‐CVI SiC‐Matrix Composite

Abstract

Thermal shock damage in a two‐dimensional woven‐Nicalon (tm) ‐fiber‐reinforced‐CVI SiC‐matrix composite was induced by water quenching and characterized by optical microscopy as a function of quench temperature difference (Δ T ) and number of quench cycles. Mechanical damage generated in flexure on quenched and unquenched specimens also was characterized and compared to the thermal shock damage. The observed thermal shock damage consisted of small matrix cracks and fiber‐matrix interfacial debonding on the surface, and large interior cracks in the matrix that formed between and parallel to the fiber cloths. At low Δ T values, only small matrix cracks on the surface were observed, and they were related to initial decreases in Young's modulus. At higher Δ T values, larger cracks between the fiber cloths in the specimen interior were observed and related to decreases in the ultimate strength. Cyclic quenching resulted in progressive thermal shock damage that was consistent with Young's modulus measurements.