Abstract: Based on mechanics of composite materials, the Tsai-Hill strength criterion expressions are derived under plane stress and plane strain conditions. The analytic solutions of modeⅠ, modeⅡand Ⅰ/Ⅱ mixed mode crack tip plastic zone are obtained for an infinite composites plate with a central crack under small scale yielding. The crack tip plastic zones are analyzed for different crack inclination angle , Poisson ratio v31 and v32. The obtained results show that the size of crack tip plastic zone under plane strain condition is less than that of crack tip plastic zone under plane stress condition, the parameters of , v31 and v32 affect the size and shape of crack tip plastic zone obviously, and the difference among crack tip plastic zone results for different value of parameters is great. In addition, the solution is applicable to composites as well as isotropy materials.

Key words: Composites, Crack, Plastic zone, Small scale yielding