TY - JOUR
T1 - Directional dependence of fracture toughness in hot-Pressed SiC-whisker reinforced alumina at room and elevated temperatures
AU - Wereszczak, Andrew A.
AU - Ferber, Mattison K.
AU - Parvizi-Majidi, Azar
PY - 1997
Y1 - 1997
N2 - The directional dependence of fracture toughness was investigated in commercially available hot-pressed SiC-whisker reinforced alumina composites at room and elevated temperatures. Whisker orientation was transversely isotropic with respect to the pressing axis in these composites. Composite bend bars were chevron-notched and loaded in four-point bending to induce stable crack propagation in two different crack systems: defined here as a combination of crack plane and direction with reference to the pressing axis. The average fracture toughness, K1c, was found to be approximately 30% less for a crack system with its crack plane parallel and crack direction perpendicular to the pressing axis compared to a crack system with both its crack plane and direction parallel to the pressing axis through 1200°C. The crack systems with the lower fracture toughness exhibited a characteristic high concentration of whiskers aligned parallel to the crack direction within the crack plane; this appeared to be associated with decreased or unpromoted crack deflection. This fracture mechanism evidently dominated the fracture process through 1200°C because measured fracture toughnesses were independent of temperature; crack-wake toughening mechanisms, whose efficiency is a function of the residual thermal stresses, are expected to be temperature-dependent.
AB - The directional dependence of fracture toughness was investigated in commercially available hot-pressed SiC-whisker reinforced alumina composites at room and elevated temperatures. Whisker orientation was transversely isotropic with respect to the pressing axis in these composites. Composite bend bars were chevron-notched and loaded in four-point bending to induce stable crack propagation in two different crack systems: defined here as a combination of crack plane and direction with reference to the pressing axis. The average fracture toughness, K1c, was found to be approximately 30% less for a crack system with its crack plane parallel and crack direction perpendicular to the pressing axis compared to a crack system with both its crack plane and direction parallel to the pressing axis through 1200°C. The crack systems with the lower fracture toughness exhibited a characteristic high concentration of whiskers aligned parallel to the crack direction within the crack plane; this appeared to be associated with decreased or unpromoted crack deflection. This fracture mechanism evidently dominated the fracture process through 1200°C because measured fracture toughnesses were independent of temperature; crack-wake toughening mechanisms, whose efficiency is a function of the residual thermal stresses, are expected to be temperature-dependent.
KW - Ceramic composite
KW - Crack deflection
KW - Elevated temperatures
KW - Fracture toughness
KW - Whisker
UR - http://www.scopus.com/inward/record.url?scp=0031347763&partnerID=8YFLogxK
U2 - 10.1177/002199839703101902
DO - 10.1177/002199839703101902
M3 - Article
AN - SCOPUS:0031347763
SN - 0021-9983
VL - 31
SP - 1905
EP - 1919
JO - Journal of Composite Materials
JF - Journal of Composite Materials
IS - 19
ER -