Study On Creep Fatigue Crack Growth Mechanism Under Complex Constraints

With the continuous development of industrial technology,the core components of the aerospace,metallurgy,chemical industries are developing toward high temperature and high pressure for the purpose of environmentally friendly and energy conservation.Therefore,to ensure the safe and reliable operation of components,the material performance requirements is higher than ever before.In the high temperature environment,the creep damage of the component is affected by multiple factors,and the major failure is caused by creep fracture.The creep fracture is considered by the engineers as a major difficulty in ensuring the safe operation of the equipment.The challenge is that creep damage is a gradual accumulation process,and the component did not show obvious signs of fracture on macroscope,thus causing serious loss of production.Therefore,the study of the Creep Crack Growth(CCG)is critical for safe and reliable operation of high temperature equipment.In-depth analysis of CCG behavior is of great significance.The traditional creep crack propagation test takes quite long time and a high cost,while the test data is complicated to deal with and the validity of the test is related to the accuracy of the device.With the development of finite element technology,numerical simulation can not only analyze CCG behavior,simulate complex three-dimensional structure,but also further analyze the strain,stress,damage and energy changes in the crack tip area.Based on the creep damage mechanics,the corresponding user subroutine is used compiled by the FORTRAN language to simulate the creep crack propagation in ABAQUS.In this paper,the influence of constraint effect on CCG behavior was studied.The effect of the constraint effect on crack growth length and initiation time is analyzed.The coupling effects of different constraint effects on CCG behavior of P92 steel at 650? were discussed.Through the comprehensive comparative analysis of the influence of these constraint effects,it can be concluded that the constraint effect of specimen shape has the greatest influence on CCG behavior,while the influence of specimen size and initial crack depth is relatively small,and the influence of these two constraints is similar.In addition,the materials widely used in aerospace industry were studied.The constitutive modeling and parameter identification of GH4169 alloy based on KR and LM models at 650? were completed,and the corresponding subroutines were compiled for numerical simulation using their constitutive equations.The mechanical behaviors of creep strain and creep damage at the crack tip area of the two models were analyzed,it can be concluded that the LM model can simulate the creep crack propagation process more accurately than the KR model.