工程实际中服役中的核电、汽车、飞机、和压力容器等结构零部件大多在复杂多轴载荷下工作，研究多轴疲劳小裂纹问题，有利于进一步从微观层次去认识疲劳裂纹从萌生到扩展各个阶段的物理本质。研究低周多轴疲劳小裂纹扩展机理与全寿命预测方法并应用到实际设计中对重大装备结构强度设计及安全服役具有重要的科学研究价值和工程实际意义。 本项目结合多轴疲劳理论、断裂力学，材料强度学等对多轴载荷下小裂纹特性进行系统的实验和理论分析，研究出变幅多轴加载下基于小裂纹扩展特性的全寿命预测方法，为实际复杂多轴加载下的结构疲劳寿命精确预测提供新的技术方法。核心研究内容包括：（1）多轴疲劳损伤机制与裂纹萌生与扩展特性实验研究；（2）变幅多轴加载下疲劳小裂纹扩展规律研究；（3）多轴载荷下小裂纹扩展速率模型的建立；（4）基于小裂纹特性的全疲劳寿命预测方法研究。

Most structural engineering components in nuclear power, automotive, aircraft, and pressure vessels in service are subjected to complex multiaxial loading, therefore, the study on multiaxial fatigue small crack problem can further understand the physical nature of the various stages from fatigue crack initiation to growth in the micro aspect. Study on the mechanism Low-cycle multiaxial fatigue small crack and total life prediction method applied to the actual design has an important scientific value and practical significance for the structural strength design of major engineering equipment and its safe service. In the project, multiaxial fatigue theory, fracture mechanics, strength theory of material are combined to investigate the total life prediction method based on the small crack growth behavior under variable amplitude multiaxial loading, which will provide new technology and methods for predicting accurately the fatigue life of the structure under actual complex multiaxial loading. The main contents of the study include: (1) experimental investigateion on the mechanism of multiaxial fatigue crack initiation and the crack propagation characteristics; (2) study on growth the law of fatigue small crack growth under variable amplitude multiaxial loading; (3) the model of multiaxial fatigue small crack growth rate; (4) The method of total fatigue life prediction based on the characteristics of small crack growth.