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R ‐Curve Behavior and Stable Crack Growth at Elevated Temperature (1500°–1650°C) in a Si 3 N 4 /SiC Nanocomposite
Author(s) -
Rouxel Tanguy,
Wakai Fumihiro,
Sakaguchi Shuji
Publication year - 1994
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1994.tb04576.x
Subject(s) - materials science , composite material , crack growth resistance curve , brittleness , intergranular corrosion , composite number , fracture mechanics , growth rate , crack closure , microstructure , geometry , mathematics
The crack growth resistance behavior and the stable crack growth regime of a Si 3 N 4 /SiC composite have been examined at high temperature (1500°–1650°C). SENB specimens were used and the load/unloading technique, with high deflection rates to ensure an elastic behavior, has been employed to estimate the crack lengths. Rising R ‐curves have been obtained with a maximum crack growth resistance almost twice as high as the initial value. Above the T g of the intergranular glassy phase, the behavior changes from brittle to visco‐plastic and, consequently, the fracture characteristics become strongly rate dependent. It is observed experimentally that in the enhanced ductile region the crack extension velocity during the stable crack propagation from a preexisting flaw decreases rapidly with time. This phenomenon has been tentatively attributed to dynamic crack‐tip stress relaxation resulting from the rapid flow of the glassy intergranular phase in the process zone. Thus, the rheological properties of the composite appear to be of major importance to gain insight into the mechanical behavior at such elevated temperatures.