Life Prediction And Analysis Of Damage Under Fatigue-Creep Condition For Disk Based On Damage Mechanics

As the heart of the aircraft, life of the aero-engine has become a key influence on life of the whole aircraft. In life management, life of key components is an important factor to determine the whole life. Thus the key components in the aero-engine life are the key to affect life of the whole equipment. In this paper, we use the hot section of aero-engine, the turbine disk as an object, in the basis of damage mechanics, consider the fatigue failure, creep failure and fatigue-creep interaction, to confirm the damage evolution models and life prediction models.Firstly, based on the continuum damage mechanics theory, a nonlinear fatigue damage accumulation model was proposed. The model is based on the assumption of isotropic damage of metallic materials, combining with the theory of thermodynamics, considering the changes of dissipation potential of metallic materials during the damage prcoess, treating the plastic strain, which will cause the fatigue crack of metallic materials, as the source of damage. Using the Manson-coffin equation, introducing the damage into the plastic strain, a fatigue damage accumulation model as well as the life prediction model was established through mathematical derivation. We selecte the area changes of S-ε curve as the damage variable. Using the aero-engine turbine disk with experimental data on the deformation of the nickel-based high temperature alloy GH4169(GH169), the proposed fatigue damage accumulation model was verified, so as the life prediction model.Secondly, a damage evolution function of creep and a creep rupture life prediction model, which are based on damage mechanics, were proposed. This model is on the basis of Norton’s law and a multiaxial creep damage model proposed by Lemaitre. Using the definition of effective stress in damage mechanics to introduce the damage into the prcess of creep evolution, we proposed a damage evolution model of creep and a creep rupture life prediction model and the creep-time related function for metallic materials. We select the changes of stress relaxation during the creep process as the damage variable. Using the aero-engine turbine disk with experimental data on the deformation of the nickel-based high temperature alloy GH4169(GH169), we verified the creep damage evolution model, creep rupture life prediction model and the creep-time related function.Finally, based on the proposed fatigue damage cumulative model and creep damage model, which are on the basis of damage mechanics, we use the common way in damage mechaincs to study the fatigue-creep interaction problem. We introduce the relationship between the number of cycles and creep time to describe the damage process fatigue-creep interaction, a fatigue-creep interaction damage evolution model was proposed. In the study of fatigue-creep interaction life prediction model, we introduce the impact of fatigue-creep interaction factor to describe the fatigue-creep interaction on life prediction model. Using the aero-engine turbine disk with the deformation of the nickel-based high temperature alloy GH4169(GH169) test data, we verified the proposed damage evolution model and life prediction model.