Polystyrene multiple crazing

The mechanisms of crack propagation in poly(methyl methacrylate) eure particularly amenable to analysis. The situation is not so simple for other polymers. For example, in polystyrene there is usually multiple crazing in the vicinity of the crack tip. In tougher polymers such as polycarbonate shear yielding as well as crazing often takes place at the crack tip. In these cases crack propagation does not occur in such a well-controlled manner as in poly (methyl methacrylate) and it is more difficult to analyse. 

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