从微孔洞起始的热冲击裂纹的数值研究——Ⅰ: 热应力分析

陶瓷材料在热冲击荷载作用下的典型破坏模式是裂纹的起始和扩展。当高温的材料或构件突然处于低温环境时,裂纹将由材料或构件的表面开始产生和发展。因此,材料表面及其表面附近的材料微结构对裂纹的起始有着非常重要的影响。实验表明:某些具有微孔洞结构的陶瓷材料比相应的密实材料的抗热冲击性能有所提高,但相关的机制目前还没有得到定量的解释。本文作者利用商业有限元软件ABAQUS,分析了受热冲击表面上的开口微孔洞、处于表面附近的闭口微孔洞周围的热应力场,以及微孔洞的大小、微孔洞与表面的距离对热应力场的影响,其目的是为进一步分析裂纹的起始和扩展做准备。数值结果表明:一般情况下,闭口微孔洞引起的应力集中比开口微孔洞引起的应力集中更为严重,特别当闭口微孔洞与表面之间的距离很小时,和没有微孔洞情况相比,闭口微孔洞引起的最大的应力集中系数超过6。

INITIATION OF CRACK FROM THE PORES IN CERAMICS UNDER THERMAL SHOCK --Ⅰ: ANALYSIS OF THERMAL STRESSES

Cracking initiating from the surface of ceramics is a typical failure mode when the ceramic with high temperature is suddenly put into air or water with low temperature. So, the microstructure of the surface and near the surface of the ceramics is one of the dominant factors for the thermal shock behaviors of the ceramics. In other words, some experimental results have shown that porous ceramics manifested good thermal shock behaviors compared with dense ceramics, but the mechanism related to the fact has not been explained quantitatively. In the present paper, with the commercial finite element method (FEM) package, ABAQUS, stress distributions on and near the surface of the ceramics under sudden temperature change, particularly around the pores on the surface (open pores) and the pores near the surface (closed pores), were analyzed. It is found that the stress concentration caused by the closed pores was more serious than that caused by the open pores.