喷丸强化的高温涡轮榫接结构高低周复合疲劳损伤机理及多尺度模拟

Turbine attachment in modern aero-engines experiences a low amplitude and high frequency vibration (namely HCF loading) combined with a high level, low frequency stress (namely LCF loading) during operation. This combined fatigue loading on the turbine attachment posts serious reliability concerns. Shot-peening is a surface modification technique used to treat metal components to introduce compressive residual stresses and modify microstructures within the surface or subsurface layers, and is widely regarded as one effective method to improve the fatigue life of the turbine attachment. However, currently several major obstacles exist, which prevents the development of an accurate model to predict the shot peening-induced improvement of fatigue life owing to the lack of: 1) multiscale simulations to quantitatively characterize the evolution of key meso- and micro-scopic quantities, such as dislocation structure, dislocation density and grain refinement, and their impacts on fatigue damage; 2) considerations of the coupling effects of high and low cyclic loading, and 3) complex geometric structures of the turbine attachment. Therefore, it is of critical importance to investigate fatigue damage mechanism in shot-peened turbine attachments under combined high-low cycle fatigue loading. A multiscale modeling approach will be employed in the project. In particular, crystal plasticity based numerical simulations of shot peening process will be performed. The evolution of dislocation and grain structures, and their contributions to fatigue damage, will be examined and quantitatively evaluated. And eventually a predictive model will be developed to assess the fatigue life of shot-peened turbine attachments under combined high-low cyclic loading. In addition, corresponding combined cycle fatigue experiments on standard specimens and component-like specimens from actual turbine attachments will be conducted to allow multi-level experimental verification of the model. This study is expected to provide more accurate fatigue life prediction for shot-peened turbine attachment under combined high-low cyclic loading, and scientific guidance to the life-time design of critical components in advanced aero-engines.

航空发动机涡轮榫接因结构和受载的双重复杂性存在高低周复合疲劳失效问题，为此，采取喷丸强化表面改性技术优化零件表层的微观组织并引入残余压应力，用以提高抗疲劳性能。目前喷丸强化的高温涡轮榫接寿命设计存在的主要问题有：①缺乏量化表征喷丸所致位错组织、位错密度、晶粒细化等微细观参量对疲劳损伤的影响机制；②尚未考虑载荷耦合与残余应力综合引起的裂纹闭合效应，以及涡轮榫接的结构特征。因此，本项目拟从喷丸强化的物理机制出发，揭示喷丸强化的涡轮榫接结构复合疲劳损伤机理并提供有效的数值模拟方法。主要包括：基于位错密度、晶粒尺寸的喷丸强化建模技术；高低周载荷耦合作用下喷丸强化对疲劳损伤的影响机制；喷丸强化的涡轮榫接结构高低周复合疲劳寿命模型；标准试件、模拟件、涡轮榫接构件的多层次试验验证。期望通过本项研究更为精确的预测喷丸强化高温涡轮结构的复合疲劳寿命，为先进航空发动机关键部件的寿命设计提供科学支持。

航空发动机涡轮榫接因结构和受载的双重复杂性存在高低周复合疲劳失效问题，因此采取喷丸强化技术来提高抗疲劳性能。目前喷丸强化的高温涡轮榫接寿命设计存在尚未掌握喷丸强化工艺对表面完整性的影响机理、缺乏量化表征喷丸所致微细观参量对疲劳损伤的影响机制以及尚未考虑高低周载荷耦合对疲劳损伤的影响机制等问题，因此无法充分发挥喷丸强化的技术优势，仅仅作为提高疲劳性能的备用手段。.本项目以涡轮榫接为对象，在喷丸强化工艺试验的基础上，发展了三种形状的喷丸强化代表性体积元模型，揭示了喷丸强化晶粒细化机制，在此基础上基于位错演化模型关联了宏细观参数，建立了喷丸强化晶粒尺寸、位错密度等微观参量数值模拟方法。基于喷丸强化后高温合金单一载荷高温疲劳试验和高低周载荷耦合试验，揭示了表面粗糙度、残余应力、微观组织等表面完整性参量对疲劳的影响机理，分别建立了单一载荷下疲劳寿命模型，探究了高低周载荷耦合作用对疲劳损伤的影响机制。在此基础上针对涡轮榫接结构，建立了DEM-FEM耦合的涡轮榫槽结构喷丸强化工艺数值模拟方法，发展了基于临界平面法和临界距离法的涡轮榫接结构高低周复合疲劳寿命模型。利用本文建立的数值模拟方法与寿命预测方法，完成了涡轮榫接结构高低周复合疲劳寿命预测，试验结果在预测寿命的3倍分散带以内，预测结果吻合较好。.通过本项目研究，进一步明确了喷丸强化工艺对表面完整性的影响机理，建立了适用于涡轮榫接复杂结构的喷丸强化数值模拟方法，发展了经试验验证的高低周复合疲劳涡轮榫接寿命预测方法，实现了喷丸强化高温涡轮榫接结构复合疲劳寿命的精准预测，有效支撑喷丸强化工艺在涡轮榫接部位的应用，为先进航空发动机关键部件的寿命设计提供科学支持，具有重要的科学意义。