| Continuum damage mechanics uses damage variables as internal state variables of a material to describe material deterioration under unfavorable conditions. In deriving the constitutive equations for damaged materials, the hypothesis of incremental complementary energy equivalence is proposed here. Based on this new hypothesis, a large damage theory is formulated, from which an anisotropic damage model is developed. Specializing the hypothesis for the isotropic damage and on the basis of the irreversible thermodynamics theory, a damage evolution model for ductile materials is formulated. The influence of the stress triaxiality and strain hardening exponent on the evolution process are analyzed. Using Dugdale's model for materials, damage distribution and size of damage zones just ahead of a macrocrack under Mode I loading are studied. Analytical results obtained are compared with those computed via a finite element analysis. Additionally, comparison of the size of plastic zones obtained by extending Dugdale's model for elastic-perfectly plastic materials to strain hardening materials is also made. Also, the effects of damage distribution and damage size on the stress intensity factor under Mode I loading are investigated. Three influence factors are considered: local fracture path deflections, a reduction in the modulus of elasticity and a release of residual stresses in the vicinity of a macrocrack. Shielding effects are produced in each of these situations. |
