航空发动机叶片表面梯度强化层裂纹扩展监测方法研究

The cold side blade locating at the front of engine suffers from fatigue crack causing by complex environment, which is a great danger to the engine reliability. Blade Tip-timing is a promising way to achieve on-line monitoring of the crack state. To enhance the fatigue strength, most of the engine blades have been treated by Laser Shock Peening. However, the gradient surface layer induced by laser shock leads new challenges to the crack monitoring. This project will firstly focus on multi-scale problem due to the gradient surface layer. From nanoscale to mesoscale perspective, a gradient coarse-grained molecular dynamics method will be proposed to study the gradient constitutive feature. By coupling the mesoscale and macroscale models, the mechanism of crack growth affected by gradient grain boundary and gradient constitutive feature will be revealed. On this basis, a method on compressed sensing of undersampling signal to obtain the reconstruction of strain field will be presented. The mapping relation between tip-timing signal and reconstructed stain field of the strengthened blade will be given thus to effectively monitor the crack growth in the gradient surface layer. Finally, experimental verification will be performed on rotor simulator platform. By means of this project, the mechanism of crack growth in the gradient surface layer and the method on reconstructing tip-timing signal of the strengthened blade are expected to be achieved. These results may provide significant support to the on-line monitoring of aero-engine at both of theoretical and technical aspects.

冷端叶片位于航空发动机最前端，其在复杂环境下产生的疲劳裂纹是威胁发动机可靠运行的重要隐患，非接触式的叶端定时为实现叶片裂纹状态在线监测提供了有效途径。为提高疲劳强度，叶片大多经过激光冲击强化，然而，由激光冲击导致的梯度表层给叶片裂纹状态监测带来了新的挑战。本项目首先针对梯度表层引发的多尺度问题，拟从微-介观尺度出发，提出梯度化介观分子动力学方法，研究材料表层梯度本构，耦合介-宏观模型，揭示梯度晶界作用与梯度本构特性下的裂纹扩展规律；在此基础上，提出叶端定时欠采样信号压缩感知应变场重构方法，阐明强化叶片叶端定时测点与应变场重构的映射关系，实现叶片表面梯度强化层裂纹扩展监测；在模拟转子实验台上开展实验验证。通过本项目的研究，可望在梯度表层裂纹扩展机理和强化叶片叶端定时信号重构方法方面有所突破，为航空发动机在线监测提供重要理论与技术支持。

本项目针对强化叶片梯度表层裂纹状态监测方法开展研究，揭示了梯度晶界作用与梯度本构特性下的裂纹扩展规律，提出了叶片裂纹演化特征与应变场的多尺度建模方法，结合叶端定时少测点与应变场重构映射机制，实现了强化叶片梯度表层裂纹扩展监测。创新点如下：.a.提出了纳米孪晶钛临界孪晶密度强化机理，建立了梯度晶界优化与梯度本构特性下的多晶钛力学模型，揭示了梯度结构影响下的多晶钛力学性能演化与裂纹扩展规律，解决了梯度结构裂纹扩展的物理与力学关联问题。.b.提出了考虑原子尺度缺陷的微-介-宏观跨尺度损伤演化模型，通过引入剪切弹性非线性和界面损伤接触，阐明了复合材料损伤演化的多尺度力学机理，解决了损伤多尺度演化过程中应变场的表征难题，实现了宏观结构件的损伤精确预测。.c.基于叶端定时测量技术，通过构造叶片动应变场稀疏重构模型，采用正交匹配追踪算法求解模型，提出了少测点欠定条件下叶片动应变场稀疏重构方法，在此基础上实现了强化叶片梯度表层裂纹扩展监测。.研究成果在《Applied Surface Science》、《Composites Part B: Engineering》、《IEEE Transactions on Instrumentation and Measurement》等权威期刊发表中英文论文10篇（其中，第一标注6篇），会议论文4篇，申请发明专利18项、其中授权专利7项，申请软件著作权1项。