Bridging stresses from R-curves of silicon nitrides
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The increasing crack resistance (R-curve) behaviour of ceramic materials is of high interest for technical applications. The initial value at the onset of crack extension is called the crack-tip toughness KI0. Very often but not in all cases a saturation of KR → KR,max is observed. Whereas silicon nitride ceramics show an increase of KR up to saturation within a few micrometers, alumina exhibits a comparably low initial steepness and shows saturation even after some mm crack extension.
Several reasons can be responsible for this effect. In coarse-grained materials, large grains can transmit tractions between the two crack faces resulting in so-called bridging stresses acting against the crack opening. As the consequence, such bridging effects shield the crack tip partially from the applied loads.
R-curve behaviour is commonly described by a relation KR = f(Δa) in which KR is the stress intensity factor necessary for crack propagation by an amount of Δa. This would be an appropriate...
KeywordsStress Intensity Factor Y2O3 Silicon Nitride Crack Opening Displacement Crack Extension
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