Effect Of Residual Stress On Creep Fatigue-Crack Growth Rate Of G115 Steel At 650?

In many industries,such as aviation and power generation,the performance of high-temperature components is facing severe requirements.They have to withstand various loads,such as equipment'start-up and shutdown,so that they served in the condition of creep-fatigue interaction.And because the internal defects caused by welding will lead to the crack propagation behavior in service,it is of great significance to study the creep-fatigue crack propagation damage mechanism.And the residual stress after welding also has an important impact on the service performance of components.In this paper,the creep-fatigue crack growth test and finite element simulation technology are used to compare and analyze the creep-fatigue crack growth damage mechanism and the effect of residual stress of the new heat-resistant steel G115.The main contents are as follows:?1?Compact tensile CT specimens of G115 was used to study the micro-mechanism of crack propagation.From initial stage to accelerated stage,the mode of crack propagation changes from transgranular to intergranular.In the initial stage,fatigue damage structures such as fatigue striations and fatigue bands were observed.After then,creep voids began to nucleate and grow up with secondary cracks.In the acceleration stage,the number of secondary cracks increased.In addition,with finite element simulation,the results show that the creep damage increases gradually and the fatigue damage decreases gradually.?2?Based on the finite element simulation of the pre-compression test of CT specimen of G115 steel,the specimen size of the maximum tensile residual stress field can be obtained.It is found that 2.5mm of notch radius and 17kN of maximum compressive load was used.In addition,the accuracy and availability of the finite element simulation results are verified by pre-compression test results and the results of X-ray detector.?3?Through creep-fatigue crack growth test of G115 steel at 650?,the effects of holding time,initial crack depth and residual stress on crack growth rate were studied.It is found that the life increases with the increase of holding time or the decrease of initial crack depth.And the effect of residual stress on the initial stage of crack growth is more significant,which can shorten the crack initiation period.With the increase of holding time or the decrease of initial crack depth,the effect of residual stress weakens.And the hook of stress intensity factors disappears with residual stress and the ?C_t?_avg parameter has a good linear relationship with the spreading rate.