基于循环孔洞扩张模型的海工钢超低周疲劳断裂分析与预测

Analysis and prediction of ultra-low cycle fatigue fracture of offshore steel based on cyclic void growth model

基于微观断裂机理的循环孔洞扩张模型是一种进行超低周疲劳断裂分析及预测的有效方法。在该方法中,孔洞扩张指数与损伤退化参数是控制裂纹扩展进程的重要参数。受生产工艺的影响,不同批次钢材的孔洞扩张指数与损伤退化参数往往存在较大差异,使得对结构的超低周疲劳断裂分析存在准确性不足的问题。为解决上述问题,本文采用光滑圆棒、平滑槽口圆棒及缺口试样开展试验,进行钢材超低周疲劳特性研究,探索试样开裂机制和损伤演化规律;其次,编写基于循环孔洞扩张模型的VUSDFLD程序,结合圆棒试验结果进行有限元分析,校准孔洞扩张指数及损伤退化参数;最后,基于前述理论和程序,开展缺口试样超低周疲劳断裂研究,分析裂纹萌生及裂纹扩展速率,并就试样的超低周疲劳断裂寿命展开预测。结果表明,基于循环孔洞扩张模型的超低周疲劳断裂进程与试验结果比对良好,适用于超低周疲劳断裂寿命预测。

The cyclic void growth model(CVGM)based on microscopic fracture mechanism is an effective method to analyze and predict ultra-low cycle fatigue(ULCF)fracture.In this method,the void growth index and damage degradation parameters are important parameters to control the crack propagation process.Due to the influence of production technology,the void growth index and damage degradation parameters of different batches of steels are often unfixed,which leads to the insufficient accuracy of the ultra-low cycle fatigue fracture analysis.In order to solve this problem,smooth round bar,smooth notch round bar and notch samples were used to carry out experiments,the ultralow cycle fatigue characteristics of steel were studied,and the cracking mechanism and damage evolution law of the samples were explored.Secondly,the VUSDFLD program based on the cyclic void growth model was written,and the finite element analysis was carried out based on the results of test to calibrate the void growth index and damage degradation parameters.Finally,the ultra-low cycle fatigue fracture of notched samples was studied,the crack initiation and crack propagation rates were analyzed,and the ultra-low cycle fatigue fracture life of the samples was predicted.The results show that the fracture process of ultra-low cycle fatigue matches well with the experimental results,which is suitable for the prediction of ultra-low cycle fatigue fracture life.