Craze, crazing

Fracture initiated in the tensile tested ABS samples, as noted also by Truss and Chadwick from either surface flaws or from internal flaws. Figure 33a shows an SEM picture of the tensile fracture surface of a sample broken at a comparatively high deformation rate of 12.7 cm/min. The fracture surface is unlike that of SAN (Fig. 27 a) or that of rubber modified polystyrene (Fig. 3 a). Fracture, for this specimen, has developed from both a surface source and from an internal source and fine radial flow lines emanate from both sources. The slow growth region adjacent to the source tends to develop a conical shape as has been noted This is probably a result of localized shear formation. In ABS specimens subject to creep deformation at low values of stress, the creep strain is found to be due almost entirely to shear but, at higher stresses, shear is accompanied by crazing Crazes can also be induced... 

Some other craze phenomena now being recognized as intrinsic crazes (crazes II) have already been discussed in Chapter 2. They will be put into context in a later section of this chapter. 

In Chapter 2 intrinsic crazing has been discussed extensively. The numerous crazes appearing for instance in amorphous PC drawn to high stresses and strains in a temperature region close to the glass transition temperature, T, were called crazes II in order to distinguish them from the ordinary type of craze (craze I) treated in most of the craze literature The results showed that under the drawing conditions... 

Crazes occur perpendicular to the Stress direction shortly before a destructive break. They may be up to 100 fitn long and up to 10 /im wide. Crazes are not hairline cracks, that is, they ate not totally void between the break surfaces. The spaces between the break surfaces in crazes mostly contain molecular bundles or lamellar material stretched in the stress direction. Consequently, in contrast to genuine breaks, crazes possess a structural and mechanical continuity. Because certain materials whiten on crazing, crazes arc often called white breaks. 

V shaped markings. The chemicals which loosen secondary valence bonds, particularly solvents, reduce the tensile stress required for crazing. Crazing and environmental stress cracking are therefore frequently initiated on surfaces accessible to chemicals. 

The characteristic mechanical property of the amorphous polymers is high strength and a brittle up to ductile deformation behavior. The reason for this behavior is the formation of localized deformation zones under load, such as crazes, deformation bands, or shear bands [12]. The typical type of deformation seen in the amorphous brittle, glassy polymers is the craze. Crazes are often visible with the naked eye in reflected light see Fig. 1.4. The word craze recalls a macroscopic crack-like appearance craze comes from an old English word. 

Craze, environmental craze Craze, intrinsic craze Craze-like deformation zones Craze, macro craze Craze, mid-rib Debonding... 

On cooling, the glaze should develop a compressive stress. Otherwise, it may develop crack-like features. The development of such features is known as crazing. Crazing is shown in Figure 16.11. Crazing develops under tensile stress. These crazes can lead to cracks. Failure under compressive stress requires substantial stress. Such a failure is called shivering. 

In some thermoplastics, the crack-formation process may be preceded by crazing crazes are regions of localized deformation and microvoids (Figure 15.9). 

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