Density of craze

Early in the study of crazing it was recognized that there was usually a time delay between the application of stress and the visual appearance of crazes. This delay time is evidence of a barrier to craze nucleation. The experimental situation may be suimnarized by Figure 1, which shows the density of crazes as a function of time under various states of stress in polystyrene (PS) from the work of Argon and... 

Fig. 1. Surface density of crazes versus time in polystyrene for several levels of hydrostatic tension or and deviatoric stress s. From Ref. , courtesy Taylor and Francis, Ltd.

Figure 3.26. Electron micrograph of an ultrathin section cut parallel to the stress-whitened surface of a commercial ABS plastic. Dark portions represent both rubber particles and craze lines stained by osmium tetroxide. Note that the rubber particles appear to encourage a high density of crazing between them. (Matsuo, 1968.)...

The density of crazes increases with increasing stress. 

Fig. 28. Scanning electron micrograph of damage occurring below crack surface in an aliphatic polyketone polymer (Ref 114). Note that the highest density of crazes occurs near the crack surface.

A quantitative analysis of craze shape and mass thickness contrast within the craze allowed Lauterwasser and Kramer [382] to derive the stress profile existing along a polystyrene craze. Kramer and his coworkers have extended this study to many other polymers, relating the mean density of craze material to entanglement density in the polymer glass and to toughness [395] without a basic change of preparation technique. 

In equation 20, A is some representative area and n becomes the number density of crazes of radius t. The representative area A is related to the representative volume V by y = 6A. Figure 18a describes how the number density of crazes and... 

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