共晶基陶瓷复合材料的断裂韧性

应用细观力学方法研究了由具有随机尺寸和方位的棒体共晶体构成的共晶基陶瓷复合材料的断裂韧性.首先根据棒状共晶体的细观结构特性,考虑共晶体边界处的微观滑移确定共晶陶瓷复合材料的开裂应力,当外载荷达到开裂应力时,裂纹开始扩展.然后分析裂纹表面处的棒状共晶体桥联力使裂纹产生闭合效应,减小裂纹尖端的应力集中,建立棒状共晶体桥联增韧机制;再依据棒状共晶体拔出过程中摩擦力做功,建立棒状共晶体拔出增韧机制.最后在棒状共晶体的桥联与拔出增韧机制的基础上,得到了共晶基陶瓷复合材料断裂韧性的理论表达式.结果表明共晶基陶瓷复合材料的断裂韧性与棒状共晶体的长径比密切相关.

FRACTURE TOUGHNESS OF EUTECTIC CERAMIC COMPOSITE

This paper presents the fracture toughness of theeutectic ceramic composite which is mainly composed of eutectic ceramic rodswith random size and orientation. Firstly, on basis of the microstructure,considering the boundary slip of eutectic rods, the cracking stress of theeutectic ceramic composite is determined. When the applied tensile stressequals to the cracking stress, the crack will grow. Secondly, we imaginethat the load carried by the eutectic ceramic rods in the crack wake willproduce a crack-closing force. It will reduces the stress intensity in frontof the crack. The bridging toughening mechanism of eutectic rods isconstructed. Thirdly, the pull-out work is given by the integral of thefrictional force over the pull-out length. The pull-out toughening mechanismof eutectic rods is obtained. And lastly, based on the bridging tougheningmechanism and the pull-out toughening mechanism, the enhanced toughnessscales with the inherent matrix toughness, and the theoretical formula offracture toughness of the eutectic ceramics composite is determined. Theresult shows that the fracture toughness of the composite is dependent onthe aspect ratio of eutectic-rod.