Introduction of Cnack-arrest Mechanism in Fiber Composites

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For practical application of advanced composite materials, further improvement of mechanical property and reliability are needed. In the present study, it was intended to introduce crack-arrest mechanism in fiber-composites for siliconcarbide fiber reinf orced titaniumaluminide intermetallic compound and siliconcarbide fiber reinofrced BMAS (crystallized glass) from theoretical and experimental standpoints. Main results are summarized as follows.(1) The energy release rate for mode I crack decreases rapidly with increasing debonding length. From this and related study, it was clarifoed that even the debonding length comparable to several times of the fiber diameter is very affective to arrest Mode I crack propagation.(2) The condition for the debonding to occur prior to the crack extension was studied from fracture mechanical approach, from which it was shown that controling the interface as to be have the mode II type energy release rate less than 0.3 times the energy release rate for mode I crack.(3) The interfacial debonding grows unstably when the volume fraction of fiber is low but stably in the early stage when it is high.(4) The influences of residula stress and frictional shear stress at the debonded interface on interfacial debonding in mulitifiber composites were clarified. A new approch to describe the fracture behavior of composites with residula stresses was developed.(5) The effects of double and gradient coatings on fiber on crack-arrest was clarified. Also it was shown that multiple cracking can be utilized for crack-arrest since the enrgy release rate at the crack tip in mode I can be reduced by reduction in crack-spacing.(6) The crack-arrest conditions for several composite systems which are promising for industrial application were derived.