基于损伤力学和XFEM的舰船蒸汽轮机叶片裂纹扩展研究

Research on blade crack propagation based on damage mechanics and XFEM

叶片作为舰船汽轮机的核心零部件,其在复杂工况下的低周疲劳寿命一直是备受关注的问题。传统的寿命预测方法大多是基于经验公式进行求解,没有考虑损伤累积对材料固有属性的影响,也没有对裂纹萌生和扩展过程进行全面的分析。文章以损伤力学的基本理论为基础,考虑叶片实际非对称循环的工作状态,引入平均应力的概念,推导叶片低周疲劳寿命的计算公式以及损伤随循环次数变化关系的表达式。同时基于有限元分析软件ABAQUS,使用XFEM方法模拟叶片裂纹扩展并进行低周疲劳寿命分析,并与所给出的理论计算结果进行对比。结果表明,所建立的基于损伤力学的低周疲劳寿命计算结果与基于扩展有限元的裂纹扩展模拟结果吻合较好,其对于舰船汽轮机叶片等工程结构的寿命预测具有一定价值。

As the core component of marine steam turbine,the fatigue life of blade in complex conditions has been a concern.Most traditional life prediction methods are based on the maximum stress or strain position of the blade during the working process.The influence of the damage accumulation on the inherent properties of the material is not considered in the methods which are based on the empirical formula,and the crack initiation life and the crack propagation life of the blade are not described completely.Based on the basic theory of damage mechanics,this paper deduces the formula of low-cycle fatigue life of blade which considers the actual nonsymmetry operating condition of turbine blade;by introducing the concept of average stress,the expression of the relationship between damage and cycle times is proposed.At the same time,based on the finite element analysis software ABAQUS,XFEM method is used to simulate the crack growth simulation and the low-cycle fatigue life analysis of the blade,and the results are compared with the theoretical calculation results.The results show that the proposed calculation method of low cycle fatigue life based on damage mechanics coincides well with the finite element method of blade crack propagation analysis,which has a certain value for the prediction of life span of steam turbine blades and other engineering structures.