Life Prediction of Long-Term Creep-Fatigue

本课题的目的是开发一种长期蠕变疲劳寿命预测方法。试验材料为sus304奥氏体不锈钢，在k进行了推拉蠕变疲劳试验，得到的主要结论如下：(1)基于静态蠕变和无保持时间低周疲劳数据，建立了长期蠕变疲劳寿命预测方法。进行了5 min和24 h不同保持时间下的应变控制疲劳试验，并获得了疲劳数据。根据ASME规范案例中蠕变/疲劳临界损伤定义的线性损伤求和规则对短期和长期蠕变-疲劳寿命进行了预测。预测结果与试验蠕变疲劳寿命吻合较好，保温时间在5min ~ 24hr之间。(2)本项目第二年将在光滑试件上发展的寿命预测方法推广到缺口试件上。对弹性应力集中系数分别为2.6、4.2和6.0的三种环形缺口试件进行了循环弹塑性蠕变有限元分析。分析的应力波为频率为0.1 Hz的三角形应力波、拉伸保持时间为166 min的梯形应力波和频率为0.0001 Hz的慢慢波。分析进行到1（1/4）个周期。根据线性损伤求和规则和应变范围划分法，计算出缺口根部的局部应力应变，并对蠕变疲劳寿命进行预测。预测寿命与试验蠕变疲劳寿命吻合，表明有限元方法适用于估算长期保持时间和慢-慢疲劳寿命。

The objective of this project is to develop a life prediction method of long term creep-fatigue.The test material used here was a SUS 304 austenitic stainless steel and the push-pull creep-fatigue test was carried out at K. the main conclusions obtained are as follows:(1)We developed a life prediction method of long term creep-fatigue based on the static creep and the no-hold-time low cycle fatigue data. The strain controlled fatigue tests with various hold-times ranging from 5 min and 24 hr were carried out and the fatigue data were generated.The life prediction was made based on the linear summation damage rule with the critical creep/fatigue damage defined in the ASME Code Case for the short and long term creep-fatigue life.The predicted results closely agreed with the experimental creep-fatigue life with the hold-times between 5min and 24hr.(2)The life prediction method developed in the smooth specimen was extended to the notched specimen in the second year of this project.The cyclic elastic-plasticcreep FEM analysis was made for the made for the three types of the circumferential notched specimens whose elastic stress concentration factors were 2.6,4.2 and 6.0. The stress waves analyzed were the triangular stress wave with frequency of 0.1 Hz,the trapezoidal stress wave with 166-min tensile hold-time and slow-slow wave with frequency of 0.0001 Hz. The analysis was made up to 1(1/4)cycle. The creep-fatigue life was predicted based on the calculated local stress/strain at the notched root from linear summation damage rule and the strain range partitioning method. The predicted life agreed with the experimental creep-fatigue life and we concluded that the FEM method was applicable to estimating the long term hold-time and slow-slow fatigue life.