NONLOCAL THEORY STUDY ON FRACTURE TOUGHNESS OF CERAMIC MATERIALS

The theoretical calculation formulas for the plane strain fracture toughness of mode Ⅰand Ⅱcracks of ceramic materials are deduced in this paper by using the nonlocal elasticity theory and maximum tensile stress criterion The deduced formulas, which are independent of crack geometry,bear a relation to material parameters.It is shown through experiment that the theoretical value of fracture toughness is the lower limit of testing value. The theoretical calculation formulas for fracture toughness relate the macro-mechanical performance of materials with the micro-structural parameters and,therefore, are beneficial to fully understanding the physical mechanism of material rupture.

陶瓷材料裂纹扩展非局部理论

本文根据非局部弹性理论推导了陶瓷材料的裂纹扩展准则。理论推导表明用非局部理论推导的裂纹扩展临界应力与临界裂纹长度都要比用线弹性断裂理论（ＬＥＦＭ）推导出来的大得多。用热压氮化硅（ＨＰ－Ｓｉ３Ｎ４）陶瓷材料在室温下做裂纹扩展实验，实验结果与理论推导吻合得较好。

超声拉伸陶瓷材料断裂机理研究

基于非局部理论对超声振动拉伸下ZrO2增韧Al2O3(ZTA)陶瓷材料的力学特性进行了研究,建立了超声振动拉伸下的非局部本构模型。通过数值模拟,研究了晶粒间距、超声振幅、频率等内外部特征变量对非局部核函数的影响规律,振幅、频率对核函数的影响均呈现下开口抛物线性形状,对核函数的影响存在一个临界值。通过超声单轴拉伸试验,对理论推导的核函数影响规律进行验证。在超声单轴拉伸实验下通过观察陶瓷断口SEM形貌,分析了裂纹扩展规律及断口微观结构的变化特征,获得了超声振幅和频率对陶瓷材料微观结构的影响规律。结果表明超声振动改变了材料的断裂方式和微观组织结构,断裂应力随着振幅和频率的增大而减小而后增大,试验得出了与非局部理论一致的结论。证实了超声振动对裂纹扩展起到了促进作用。