Kinetics of craze formation in glassy polymers

Craze initiation and propagation near a Griffith crack were studied in poly(methyl methacrylate) and polycarbonate. Craze propagation results either in eventual catastrophic failure or in termination of propagation. Photoelastic observations indicate that high stress concentration at the initial crack tip is relieved immediately after craze initiation and craze propagation introduces no new stress concentration at the craze front. These results lead to the conclusion that the criteria for craze initiation and propagation are described fairly well by the stress intensity factor. A fracture mechanics model proposed by Marshall et al. can explain the kinetics of craze propagation in poly(methyl methacrylate). However the growth rates are lower in polycarbonate than in poly(methyl methacrylate). This is attributed to the difference in a penetrant activity.