Damage Mechanics Approach to the Prediction of Deterioration and Fracture Process of High-Temperature Structural Materials

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The present project aims at the development of a local approach to damage and fracture analysis of high-temperature structural components based on Continuum Damage Mechanics (CDM) and Finite Element Method (FEM). A systematic and unified procedure to simulate the whole process ranging from the damage initiation to the final fracture due to crack growth was discussed. The major results of the present project are summarized follows :1) As a theoretical basis of the present approach, a systematic formulation of damage evolution equations under general condition of loading was developed on the basis of irreversible thermodynamic theory for constitutive theory. An evolution equation of elastic-plastic damage in polycrystalline materials under multiaxial state of loading was developed. The existence of damage surface and its evolution were discussed.2) Formulation of inelastic constitutive equations for the accurate analysis of damage and fracture process of high-temperature structures was d … More iscussed. The hardening mechanisms under proportional and non-proportional cyclic loading were elucidate, and were incorporated to formulate elaborate inelastic constitutive equations of cyclic plasticity.3) Problems intrinsic to the numerical procedure of the local approach to damage and fracture analysis based on CDM and FEM were discussed. It was elucidated that the causes of mesh-dependence of the numerical results consist not only in the stress singularity at the crack tips but also on the mathematical stability of the damage evolution equations.4) In order to avoid the mesh-dependence of crack growth rate, basides incorporation of perfect plasticity and a method of stress limitation at crack tips, a method of stochastic distribution of the critical damage values was proposed.5) The resulting computer algorithm of damage and fracture analysis was applied to simulate the process of creep crack growth from two circular holes in the structural element at high-temperature. Damage and fracture process in the whole domain of the structural element was displayd on the computer. Comparison with the corresponding experimental observation was also discussed. Less