Numerical Study Of The Different Constraints Effect On Creep Crack Growth Behavior

In the development of modern industries,the core components are forced to serve at elevated temperatures and high pressure due to the request of improving energy utilization and reducing the emission of harmful gas,especially in the areas like aviation,chemical industries and power plants,which requires the material to be equipped with better properties.Creep crack growth is the main reason accounting for the failure of components working under high temperatures and if the damaging procession failed to be controlled properly,disasters can be resulted because of the poor working conditions.The creep crack damage accumulation within components is affected by the temperature of the environment,the working load and the geometries of the components.The time duration between the formation of micro cracks and the rupture of working parts is quite long,which makes the creep rupture issue a tough problem for the engineers.To ensure the facilities working at elevated temperatures run safely,accurate evaluation of the service life of components is needed,and the most important aspect is to investigate the creep crack growth(CCG)behavior of materials.Performing experiments of the CCG is both time consuming and difficult,whereas the finite element analysis is not only precise and efficient for the exploration of the CCG behavior,but also convenient for the study of stress and strain rate field near the crack tip.In this paper,based on the creep damage mechanics,the CCG behavior simulation is realized by the ABAQUS user routine programmed with FORTRAN language,and the finite element results turned out to be consistent with the experimental outcome.The constraint effect at the crack tip has significant influence on the CCG behavior.Based on the previous studies,the effect of specimen geometries,sizes and the initial crack length on the CCG behavior is investigated,especially the impact of constraint effect on the initiation of crack and the CCG rate.In addition,a creative point of the research is that the horizontal comparison is made regarding to the impact of different constraints on the creep crack behavior and the results are as follows: the impact of specimen geometries is much greater than the sizes;the specimen sizes has similar impact as the initial crack length.Finally,the depth and angles of specimen grooves is studied systematically,especially the impact of specimen grooves on the crack initiation time,the crack tip morphology and the CCG rate.The stress triaxiality and equivalent stress of different specimens is analyzed,and internal mechanism of how the specimen grooves affect the CCG rate is covered using the theory of mechanics.