Computational methods for creep fracture analysis by damage mechanics

Some mechanical problems of the computational method of creep fracture analysis based on continuum damage mechanics are discussed. After brief review of the local approach to creep crack growth analysis by means of finite element analysis and continuum damage mechanics. intrinsic feature of the fracture analysis in the framework of continuum theory and the causes of mesh-dependence of the numerical results are discussed. Then, a series of numerical analyses are performed for a plate specimen with a central crack to show the characteristics of the mesh-dependence. In view of these results, the effects of stress-singularity at the crack tip as an essential cause of the mesh-dependence are discussed by analyzing the magnitude of stress in the finite element at the crack-tip. As another major cause of the mesh-dependence of the numerical results, ill-natured stress-sensitivity of the constitutive and the evolution equation of the conventional Kachanov-Rabotnov creep damage theory is elucidated by performing sensitivity analysis of the relevant equations. In order to suppress this singular stress sensitivity at the critical stage of damage, a new creep damage model is developed. Finally, the effects of the preceding damage held on stress singularity of the asymptotic stress field at mode I creep crack are analyzed to furnish a criterion to overcome the mesh-dependence in computational method for creep fracture analysis. (C) 2000 Elsevier Science S.A. All rights reserved.