强拘束效应下三维弹塑性疲劳裂纹扩展内聚区模型研究

Damage tolerant design has become a necessary design step for high performance parts in aero engines, hence, assessment of fatigue cracks is the key technology in modern aero engine development. Since the Paris law is not applicable for elastic-plastic cracking, a life prediction model has to be built for low cycle fatigue crack growth and a reliable assessment method is still missing. For this reason, the cohesive zone model has been a keen research topic in international fracture and damage mechanics community. The present project is investigating the cohesive zone model for nickel-based alloy of aero engines under both monotonic and cyclic loading conditions and attempting to establish a uniform assessment methodology for both rupture and fatigue failure. The project starts with identification of material deformation and damage in a small notched tensile specimen to approach the mechanical behavior of the cohesive zone. The experiment should provide the detailed information about damage development and effects of the stress triaxiality. The cohesive zone model will be introduced based on the experiments and verified in 3D FEM computations. The investigation should carry out the inter-dependence among the constrain effects, the cohesive zone model and fatigue crack growth. The systematical material testing and fracture experiments should generate sufficient experimental data base for identifying the damage evolution equation of the cohesive zone model and finite element computations, which form the reliable relationship between local stress/strain distributions and global loads. Introducing the stress triaxiality into the cyclic cohesive zone model should be able to give more accurate prediction of elastic-plastic fatigue crack growth and the fatigue life of the mechanical parts. The project should generate a uniform computational model for both rupture and fatigue crack propagation.

损伤容限设计已成为航空发动机高性能零件的必要设计内容，使疲劳裂纹评估成为这些产品研发的关键技术。然而对于低循环疲劳寿命问题，由于Paris理论的失效，导致目前缺乏有效的弹塑性疲劳裂纹计算模型和评估方法，使内聚区模型成为近年国际上断裂损伤力学研究的热点。本项目根据航空发动机镍基高温合金零件设计需要，从单调载荷裂纹扩展和疲劳裂纹扩展两个方面研究强拘束效应下三维裂纹内聚区模型，以建立统一的内聚区理论和计算方法。首先用原位拉伸仪测试平板缺口试件变形和损伤来模拟内聚区的力学行为，量化应力三轴度和材料失效关联；然后用裂纹试件验证与修正模型，建立拘束效应、内聚区方程和疲劳裂纹扩展的映射联系；再通过系统的材料和裂纹试验，获取内聚区模型和损伤演化方程所需的疲劳数据，充分利用损伤力学和有限元计算，在内聚区模型中引入应力三轴度以表征拘束效应对裂纹扩展的影响，建立三维疲劳内聚区模型，完善损伤容限设计理论。

损伤容限设计已成为航空发动机高性能零件的必要设计内容，使疲劳裂纹评估成为这些产品研发的关键技术。然而对于低循环疲劳寿命问题，由于Paris理论的失效，导致目前缺乏有效的弹塑性疲劳裂纹计算模型和评估方法，使内聚区模型成为近年国际上断裂损伤力学研究的热点。本项目根据航空发动机镍基高温合金零件设计需要，从单调载荷裂纹扩展和疲劳裂纹扩展两个方面研究强拘束效应下三维裂纹内聚区模型，以建立统一的内聚区理论和计算方法。首先用原位拉伸仪测试平板缺口试件变形和损伤来模拟内聚区的力学行为，量化应力三轴度和材料失效关联；然后用裂纹试件验证与修正模型，建立拘束效应、内聚区方程和疲劳裂纹扩展的映射联系；再通过系统的材料和裂纹试验，获取内聚区模型和损伤演化方程所需的疲劳数据，充分利用损伤力学和有限元计算，在内聚区模型中引入应力三轴度以表征拘束效应对裂纹扩展的影响，建立三维疲劳内聚区模型，完善损伤容限设计理论。