基于临界失效能密度判据的热障涂层热震损伤行为研究

目的探索热障涂层系统(TBCs)在热震过程中的损伤行为。方法基于材料能量储存极限,推导了适用于平面复杂应力情形的温度相关性临界失效能密度判据,进而利用该临界失效能密度判据与ABAQUS有限元软件相结合,研究了热生长氧化层(TGO)凸起的热障涂层系统在冷却热震过程中的损伤行为。结果对于TGO层凸起的热障涂层系统,计算了冷却热震过程中陶瓷层(TC)和TGO层的失效能密度分布云图,并根据最大失效能分布情况分析了TBCs在热震过程中各层材料的可能破坏位置,所得结果与实验吻合较好。在对TBCs的冷却热震损伤行为模拟计算中发现,当TC层的强度比较低时,热震会使TC层上表面产生往内部扩展的垂直裂纹;当TC层强度达到某一定值时,首先发生热震破坏的位置由TC层上表面变成了TGO层与粘结层(BC)的界面处,即TBCs的各层破坏顺序发生了变化。结论使用临界失效能密度准则来判断热障涂层在冷却热震过程中的损伤行为,比单纯使用某一方向应力更为准确,并能准确判断损伤起始位置和演化情况,从而更全面地反映热障涂层在热震过程中的损伤破坏行为。

Thermal Shock Damage Behaviour of Thermal Barrier Coatings Based on the Failure Energy Density Criteria

The work aims to investigate the damage behavior of thermal barrier coating system (TBCs) during the thermal shock. The temperature-dependent failure energy density criteria was deduced based on the energy storage limitation of material for plane complex stress condition. With the criteria and ABAQUS finite element software, thermal shock damage behavior of raised TBCs in the thermally grown oxide (TGO) was studied. The distribution of failure energy density in top-coat (TC) and TGO during cooling thermal shock was calculated for the raised TBCs in TGO and the damaged location of each layer in TBCs during the thermal shock was analyzed according to the maximum failure energy distribution. The obtained results agreed well with the experiment results. Furthermore, the simulation of thermal shock damage evolution behavior for TBCs showed that vertical cracks growth towards inside layer could be produced in TC under thermal shock when the strength of TC was relative lower. However, the firstly damaged location could change to the interface between TGO and BC (bond-coat) from the upper surface of TC when the strength of TC reached a certain value. The damage order of each layer in TBCs changed. Therefore, the failure energy density criteria is more accurate to characterize the thermal shock damage behavior of TBCs than the stress of one direction and can also determine the exact location of damage initiation and the evolution of damage, thus revealing the thermal shock failure for TBCs comprehensively.