ABSTRACT
The model of frictional sliding of preexisting cracks which can lead to the formation of tension cracks at their tips has been studied by a number of investigators (Kachanov , 1 9 8 2 ; N e m a t - N a s s e r and Hor i i , 1 9 8 2 ; Horii and N e m a t - N a s s e r , 1983, 1985, 1 9 8 6 ; Steif, 1984 ; N e m a t - N a s s e r and Obata , 1988 ; Ashby and Sammis , 1990 ; Fanella and Krajcinovic , 1988 ; Krajcinovic et al . , 1991, Ju , 1991 ; and Lee and Ju , 1991 ) . These damage models , nevertheless , are re stricted to Taylor's models or self-consistent models . For Taylor's models , microcrack interaction effects are entirely ignored . Although the self-consistent models are capable of accounting for weak or mod erate microcrack interaction, it is very complex for calculating the over all moduli of brittle solids which become nonsymmetric and anisotropic due to frictional sliding of closed microcracks (Ju , 1991 ; Lee and Ju , 1991 ) . Furthermore , the microcrack evolution analyses( Ju , 1991 ; Lee and Ju , 1991 ) are still restricted to Taylor's models .
