DAMAGE EVOLUTION AND RUPTURE IN CREEPING OF POROUS MATERIALS

The configurational evolution in time and space of two-dimensional ellipsoidal damage into an elongated flaw with preferred orientation is solved and studied. The damage is represented as a single, traction free, ellipsoidal void embedded in an infinitely large time-dependent porous-like solid. The solid creeps in a power-law fashion under static biaxial loads which induce a large-scale rotation (with volume enlargement/contraction) of the void. In the special case of unidirectional loading the free boundary of the void evolves into an expanded and elongated new shape while rotating towards a position codirectional with the principal tensile axis. The process simulation agrees well with visual observations of void expansion and rotation in a highly viscous material and with experimental measurements of the rupture ductilities of creeping materials with different strain-rate sensitivity index. Similarities and dissimilarities with existing phenomenological damage theories are discussed.