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Computational modeling of failure in thermal barrier coatings under cyclic thermal loads.

机译：循环热负荷下热障涂层失效的计算模型。

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摘要

In this dissertation, finite element models are used to investigate catastrophic failure of thermal barrier coatings (TBCs) due to delaminations along susceptible interfaces of thermally grown oxide (TGO) with the ceramic top coat and the inter-metallic bond coat. The materials and geometries in the studies are chosen to be representative of TBC materials in real applications.;The characteristics of the failure modes along the TGO and bond coat interface (e.g. buckling instability and strain energy driven delamination propagation) are investigated using thermo-elastic finite element models. The solution of a linear elastic eigen-value problem determines the onset of the buckling instability with a pre-existing delamination between bond coat and the TGO. The virtual crack extension method is employed to study strain energy release rate driven interfacial delamination at wavy interfaces. The materials and geometries in the study are chosen to be representative of TBC materials in real applications. Extensive sensitivity analyses are conducted to identify the critical design parameters affecting the onset of buckling and extension of interfacial delamination, as well as to develop parametric relations that enhance the understanding of these mechanisms. Finally, a numerical exercise demonstrates that the buckling instability is the leading failure mechanism at flat interfaces or at the locations of minimum cross-section in a wavy interface. However, in the vicinity of waviness, crack extension becomes a dominant mode of failure.;The top coat crack initiation and propagation is investigated using a thermo-elastic finite element model with bond coat creep. Cracks are assumed to initiate when the maximum principal stress exceeds rupture stress of the top coat. A sensitivity analysis estimates the contribution of geometric and material parameters and forms a basis to develop parametric relation to estimate maximum principal stress. Subsequently, crack propagation simulations using a hysteretic cohesive zone model are performed for parametric combinations which initiate cracks away from the interface. These analyses conclude that parametric combinations initiating top coat cracks also assist in propagation and eventual delamination of TGO and top coat interface.;A homogenization based continuum damage mechanics (HCDM) modeling framework is proposed for TBC failure effects of top coat microstructural defects. An extended Voronoi cell finite element (X-VCFEM) is employed to perform the micromechanical analysis of RVE and the results show that HCDM model has limited validity due to loss of material stability with significant damage. A sensitivity analysis reveals that the range of HCDM validity is dependent on top coat cohesive energy.
机译：本文采用有限元模型研究了热障涂层与陶瓷面涂层和金属间结合涂层沿易感界面的分层引起的热障涂层的灾难性破坏。选择研究中的材料和几何形状来代表实际应用中的TBC材料。；使用热弹性研究沿TGO和粘结层界面的破坏模式特征（例如屈曲不稳定性和应变能驱动的分层传播）有限元模型。线性弹性本征值问题的解决方案决定了屈曲不稳定性的开始，并在粘结层和TGO之间预先存在分层。虚拟裂纹扩展方法用于研究应变能释放速率驱动的波浪界面界面分层。选择研究中的材料和几何形状以代表实际应用中的TBC材料。进行了广泛的敏感性分析，以识别影响屈曲和界面分层扩展的关键设计参数，并建立参数关系以增强对这些机理的理解。最后，数值模拟表明，屈曲不稳定性是平面界面或波浪界面中最小横截面位置的主要失效机理。然而，在波纹度附近，裂纹扩展成为破坏的主要方式。;使用结合涂层蠕变的热弹性有限元模型研究了面涂层裂纹的萌生和扩展。当最大主应力超过面漆的破裂应力时，假定会产生裂纹。敏感性分析估计几何和材料参数的贡献，并形成开发参数关系以估计最大主应力的基础。随后，针对参数组合执行了使用滞后粘性区模型的裂纹扩展模拟，该参数组合引发了远离界面的裂纹。这些分析得出的结论是，引发顶涂层裂纹的参数组合也有助于TGO和顶涂层界面的传播和最终分层。；针对顶涂层微结构缺陷的TBC破坏效应，提出了一种基于均质化的连续损伤力学（HCDM）建模框架。采用扩展的Voronoi细胞有限元（X-VCFEM）进行RVE的微力学分析，结果表明HCDM模型由于材料稳定性的损失而受到严重破坏，因此有效性有限。敏感性分析表明，HCDM有效性的范围取决于面漆的内聚能。

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  • 作者

    Bhatnagar, Himanshu.;

  • 作者单位

    The Ohio State University.;

  • 授予单位 The Ohio State University.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2008
  • 页码 219 p.
  • 总页数 219
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;
  • 关键词

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