Criteria for craze initiation

With respect to general criteria for craze initiation and growth, important contributions have been made for amorphous glassy polymers by many investigators during past years. Recognizing that crazing is also inherently a cavitational process for crystalline polymers leads to the criterion that craze initiation involves a dilatational stress component. In... 

A fine entanglement network with small meshes deforms in a dense pattern of small stretched meshes in a homogeneous manner (Fig. 1.10(b)) [13]. There are several criteria for craze initiation and growth, reviewed in [5, 13,17]. 

Some criteria have been proposed for craze initiation. The earliest criterion states that crazing occurs when the uniaxial tensile stress reaches a critical value (27). Since the crazing stress depends on the strain rate and... 

Craze Initiation. Although the effect of multiaxial states of stress on the brittle and ductile failure of isotropic polymers is sufficiently well represented by the above classical failure criteria, this is not the case for crazing or the failure of anisotropic polymers, ie, oriented sheets, fibers, single crystals, etc. For craze initiation we will cite the stress-bias criterion as proposed by Stemstein (54) ... 

The criteria (Eqs. 11 and 12) are similar and are derived from studies on materials that are elastic at initiation of crazing, while more ductile materials like polycarbonate show a more pronounced sensitivity to the hydrostatic tension. This has been found experimentally by Ishikawa and coworkers [1, 27] for notched specimens of polycarbonate. Crazing appears ahead of the notch root, at the intersection of well-developed shear bands. From a slip fine field analysis, the tip of the plastic zone corresponds to the location of the maximum hydrostatic stress. This has been confirmed by Lai and Van der Giessen [8] with a more realistic material constitutive law. Therefore, Ishikawa and coworkers [1,27] suggested the use of a criterion for initiation based on a critical hydrostatic stress. Such a stress state condition can be expressed by Eq. 11 with erg = 0 and I r = B°/A°. Thus, the criterion (Eq. 11) can be considered general enough to describe craze initiation in many glassy polymers. For the case of polycarbonate, a similar criterion is proposed in [28] as... 

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