EDGE CRACKING BEHAVIOR OF A COATED HOLLOW CYLINDER DUE TO THERMAL CONVECTION
PengZhongfu1, ChenXuejun1,2, 1.Department of Applied Mechanics, University of Science and Technology Beijing, Beijing 100083, China2.Beijing Key Laboratory for Magneto-Photoelectrical Composite and Interface Science, University of Science and Technology Beijing, Beijing 100083, China 中图分类号:O346.1 文献标识码:A
关键词:热对流;涂层;边裂;权函数;应力强度因子 Abstract Edge cracking is one of major damage modes for coatings subjected to thermal transients. After penetrating across coating thickness, edge cracks usually cause interfacial decohesion and hence result in the detachment of coating from substrate, which leads to the ultimate loss of the protective effect on the substrate. The edge cracking behavior due to thermal convection is studied in this paper for a coated hollow cylinder, where the thermal stress intensity factor is used to characterize the crack driving force. Firstly, by using the Laplace transform technique, closed-form solutions are obtained for the transient temperature as well as thermal stresses. Secondly, the weight function for an edge crack in a coated hollow cylinder is determined by using the three-parameter method proposed by Fett et al. Finally, the thermal stress intensity factor at the edge crack tip is evaluated based on the principle of superposition and the derived weight function. The dependence of the normalized thermal stress intensity factor is examined on the normalized time, edge crack depth, substrate/coating thickness ratio as well as thermal convection severity. It is shown that the peak thermal stress intensity factor occurs neither at the very beginning nor at the thermal steady state of a thermal transient, but at an intermediate instant. The severer thermal convection generates a peak thermal stress intensity factor not only higher in magnitude but also earlier in time. Should other conditions remain invariant, the thermal stress intensity factor is a decreasing function of the edge crack depth; a thicker coating or a thinner substrate may enhance the thermal transient resistance of a coating.
(1) 边缘裂纹的热应力强度因子峰值既非发生在热载荷初始时刻,也非发生在热稳态时刻,而出现在时间历程的中间时刻. 用热稳态分析来代替热瞬态分析将严重低估瞬态热载荷的破坏程度. (2) 裂纹长度、基体/涂层厚度比及热流强度显著影响热应力强度因子. 其他条件相同时,随着裂纹长度的增大,筒壁边缘裂纹的热应力强度因子降低;增大涂层厚度或减小基体厚度可增强涂层抵抗瞬态热载荷的能力;增大热流强度不仅使热应力强度因子的峰值增大,而且令峰值的发生时刻提前. The authors have declared that no competing interests exist.
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