Kinetics of crack tip craze zone before and during fracture

Irreversible deformations form the main energy consumption routes for absorbing supplied energy and thus determine the resistance of materials to fracture. In many polymeric materials under mode-I loading conditions three regions of irreversible deformation behavior can be distinguished as a function of the stress intensity factor K_I or strain energy release rate G_I, respectively:

• no crack growth for K_i < K_Io
• slow crack growth for K_Io < K_I < K_Ic
• rapid crack propagation for K_I < K_Ic

In the three regions the amount and geometrical extent of irreversible deformations may be different and the influence of time, crack speed, and temperature may generate different results. In this paper the influences of time and crack speed on the kinetics of the craze zone at the crack tip will be considered in some detail, with respect to results mainly obtained for poly(methyl methacrylate), PMMA, of high molecular weight under quasi-static loading conditions.