Investigation Of Creep Crack Growth Of P92 Steel Under Unsteady And Steady State

Creep crack growth(CCG)is the major failing cause of components working under high temperature.Creep crack is difficult to detect and control at the very beginning,while at the tertiary stage,it will progress at a high rate.Thus,the components with creep crack tends to fail suddenly when workers have no preparations,which leads to great loss to industries and humanity.For many years,numerous researchers have devoted to the investigation of CCG behavior,which laid a solid foundation to the development of this subject.However,the effect of crack depth and specimen geometries on the C(t)parameter,and the different strains at crack tip,are still lack of systematic research.In this paper,numerical simulations using the ABAQUS code was conducted on different stages of CCG behavior with P92 steel and the main results are summarized as following:(1)Before the CCG behavior starts its steady state,the stress and strain rate field at crack tip is still HRR field.Although it is only a short period of time,mistakes can be resulted if this stage is ignored.In this paper,the unsteady state of CCG behavior was studied.Specimens with different crack depth and geometries were adopted,and each was modeled by ABAQUS.The C(t)integral and stress filed at the crack tip was analyzed.The results showed that as the initial creep crack goes deeper,the value of C(t)integral becomes smaller.The value of C(t)integral of different specimens is: CST specimen>CT specimen>SENT specimen.(2)The steady state of CCG behavior was studied based on the ductile exhaustion model.In this study,USDFLD subroutine was compiled and connected to ABAQUS to simulate the creep damage and CCG behavior.The crack initiation and failure,CCG rate and the different stress field at crack tip were all investigated.The results show that as the initial crack length increases,the creep crack initial time decreases and the CCG rate increases.The CST specimen shows the shortest crack initial time and fastest CCG rate during steady state,the CCG rate of CT specimen is higher than SENT specimen.Ac can be used to characterize CCG behavior at crack tip and its application in predicting CCG life needs further investigation.(3)According to results of FE analysis,the area of Mises stress and crack tip open stress increases quickly as creep crack growth under unsteady state,while shows little change during steady state.The creep damage propagates steadily after a short period of unstable stage.The area of equivalent creep strain increases quickly and extends to the whole area of crack tip.