Introduction of strengthening and toughening mechanisms into intermetallic and ceramic matrix composites

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Fiber-reniforced intermetallic and ceramic matrix composites are expected as the high temperature materials for next generation. The strength and toughness are, however, not sufficient for application. Further strengthening and toughening, and improvement of reliability are required for practical use. The aim of the present workwas to achieve high strength and toughness by introducing crack arrest mechanisms.Main results are summarized as follows.(1) Newmodelwas developed fordescriptionofmicro-damageaccumulationprocess and its influenceonoverall stress-straincurve, strengthand fracturemorphology. With thismethod, indications formaterial design to achieve high strength and toughness could be obtained.(2) Influences of residual stresses, sample size and loading condition on longitudinal cracking were clarified experimentally and theoretically, which supplied useful indications for toughening.(3) Influences of inter facial condition on unnotched and notched strengths were clarified experimentally, from which the necessary condition for crack-arrest was obtained.(4) In the Si-Ti-C-0/BMAS composite with heat-resistant crystallized glass matrix, the formation of carbon layer at interface was found to act to cause longitudinal cracking, which leads to blunting of the notch-tip. The critical energy release rate of longitudinal crackingwas first estimated to be around 100J/m2.(5) To aim toughening by inter facial control and introduction of ductile metal, C/C-Mg composite was prepared, which showed high Young's modulus, high strength and low notch-sensitivity.