基于缺陷安全衰减路径仿真的含埋藏裂纹压力容器剩余寿命研究

Study on Residual Life of Pressure Vessels with Immerged Cracks Based on Defect Security Attenuation Path Simulation

裂纹的扩展行为研究是压力容器剩余寿命预测的关键与基础,针对压力容器含埋藏裂纹的安全程度评价问题,在埋藏裂纹的安全衰减路径仿真基础上,提出了一种预测埋藏裂纹剩余寿命的计算方法。首先通过对Paris疲劳裂纹扩展公式进行迭代运算,建立裂纹长度和深度的几何关联变化模型,利用该关联模型在R6评价图上仿真模拟埋藏裂纹缺陷的安全衰减路径轨迹,其路径轨迹表征的裂纹变化过程可分为埋藏裂纹阶段和表面裂纹阶段。采用数字积分方法求解不同阶段的安全衰减路径的剩余轨迹线段,并以此为度量建立埋藏裂纹安全裕度的计算模型,该计算模型能够给出裂纹缺陷在任何尺寸时对应的动态安全裕度,并以此来反应压力容器的安全程度。通过建立压力容器裂纹缺陷的受力模型,利用有限元方法分别计算出裂纹特殊点的应力强度因子,并运用权函数法,求出裂纹缺陷应力强度因子幅K的函数表达式;采用对Paris公式进行积分的方法求出疲劳循环次数N的函数表达式,根据裂纹长度和深度的几何关联变化模型,采用分布积分的方法计算出埋藏裂纹的疲劳循环次数,从而能够有效的对压力容器含埋藏裂纹的剩余寿命进行预测。

The study of crack propagation is the key and foundation of pressure vessels’residual life prediction.In view of security assessment for pressure vessels with immerged cracks,based on the security attenuation path simulation,another calculation method is put forward to predict the residual life.First of all,the iterative calculation based on Paris fatigue crack growth formula is conducted to build the model of geometric correlation change in crack length and depth.Next,this correlation model is used to simulate the security attenuation path track of immersed crack defects in R6 evaluation diagram.The immersed crack change represented by path track can be divided into immersed crack phase and surface crack phase.Then the numerical integration method is adopted to get the residual track segment of security attenuation path in different phases,and the calculation model of immersed crack safety margin is built.This calculation model can show related dynamic safety margins for different sizes of crack defect,and reflect the safety degree of pressure vessels.After building the mechanical model of pressure vessels’crack defect,the stress intensity factor of special crack point in finite element method is calculated.And weight function method is adopted to get the function formula of the stress intensity factor range K of crack defect.The function formula of fatigue circulation time N is calculate by Paris formula integral.Lastly,according to the model of geometric correlation change in crack length and depth,the fatigue circulation times of immersed cracks is calculated by means of integration.