Phase-Field Fracture Modelling for Lifetime Assessment of Thermal Barrier Coatings

燃气轮机被广泛用于发电和推动飞机。日益稀缺的资源，保持竞争力的需要，以及气候变化，正在推动英国能源市场及其航空航天行业对效率、可靠性和减排的要求。作为热机，涡轮入口处的气体温度要求尽可能高，以最大化效率，因此，发动机这一部分的金属部件被涂上热障涂层(TBCs)以防止它们熔化。燃气轮机效率、可靠性和减排的进一步提高，绝对需要进一步改进燃气轮机。优化的TBCs将允许显著提高气体温度，以提高效率，并将更耐用。优化热障涂层的部分障碍是尚未实现对热障涂层失效的完全机械性理解。这样的理解将有助于及时维护，避免计划外停机，并支持和直接开发新的优化TBC材料系统。这项PHD研究将发展界面断裂力学的相场方法来研究薄膜中的裂纹，以及多层热障涂层的气泡形核和层裂。也许相场断裂方法最吸引人的特点是，裂纹萌生和裂纹路径是从耦合弹性能和断裂能的最小化问题中自动获得的。因此，它有望成为研究这一研究挑战的有力工具。实验工作也可能完成，结果将用于检验预测的有效性。

Gas turbines are widely used to generate electricity and to propel aircraft. Increasingly scarce resources, the need to remain competitive, and climate change are driving the UK's energy market and its aerospace industry to demand efficiency, reliability and emissions reduction. Being heat engines, the gas temperature at the entry to the turbine is required to be as high as possible to maximise efficiency, and consequently, metallic components in this part of the engine are coated in thermal barrier coatings (TBCs) to protect them from melting. Further increases in gas turbine efficiency, reliability and emissions reduction absolutely necessitate further improvements to TBCs. Optimised TBCs would allow significantly higher gas temperatures to increase efficiency and will be more durable. Part of the barrier to optimising TBCs is that a complete mechanistic understanding of TBC failure has not yet been achieved. Such an understanding would facilitate timely maintenance, avoid unplanned down time, and underpin and direct development of new optimised TBC material systems. This PhD research will develop the phase field method for interface fracture mechanics to study cracking in thin films, and blister nucleation and spallation of multi-layer TBCs. Perhaps the most attractive characteristic of phase-field approaches to fracture is that crack initiation and crack paths are automatically obtained from a minimization problem that couples the elastic and fracture energies. As such, it is expected to be a powerful tool to investigate this research challenge. Experimental work may also be completed, with the results used to test the validity of predictions.