类裂纹不连续区高温蠕变疲劳评价方法对比

Comparative research on creep-fatigue damage assessment methods for the crack-like discontinuity

反应堆存在大量由于焊接造成的类裂纹不连续区,在高温条件下较连续结构更易发生蠕变-疲劳断裂失效。以压力容器贯穿件的类裂纹不连续区为对象,分别基于ASME NH和RCC-MRx规范中的高温蠕变-疲劳评价方法进行了蠕变-疲劳损伤分析,并揭示了RCC-MRx规范特征距离的选取原理。结果表明,在类裂纹不连续区,相比RCC-MRx规范基于等效应力原理的σ-d特征距离方法,ASME NH规范的等效应力集中因子难以精确求取,同时蠕变参数对一次应力较为敏感,导致随着应力集中程度由低变高,蠕变和疲劳损伤系数由略保守变为不保守。建议使用RCC-MRx规范对类裂纹区域进行高温蠕变-疲劳评定。

There is a large quantity of crack-like discontinuities caused by the welding process.The structures with crack-like discontinuities at high temperature become more susceptible to the creep rupture failure and fatigue damage.Based on the crack-like discontinuity of the welding zone of a penetration structure,the creep-fatigue damage analysis was carried out by ASME NH and RCC-MRx elevated temperature design(ETD)codes,and the determination mechanism of the characteristic distance in RCC-MRx was revealed.The results show that,for the crack-like discontinuity,compared to theσ-d approach based on the equivalent-stress principle in RCC-MRx,it is difficult to determine the equivalent stress concentration factor accurately,while the creep parameters are sensitive to primary stresses,as a result,with the variation of the stress concentration level from non-significant to significant,the creep and fatigue damage coefficient shows a change tendency from slightly conservative to non-conservative.It′s recommended that the high-temperature creep-fatigue damage assessments should be carried out for the crack-like region using RCC-MRx code.