Craze/crack

Nomnetallics As stated, corrosion of metals apphes specifically to chemical or electrochemical attack. The deterioration of plastics and other nonmetallic materials, which are susceptible to sweUing crazing, cracking, softening, and so on, is essentially physiochemical rather than electrochemical in nature. Nonmetallic materials can either be rapidly deteriorated when exposed to a particular enviromnent or, at the other extreme, be practicidly unaffected. Under some conditions, a nonmetallic may show evidence of gradual deterioration. However, it is seldom possible to evaluate its chemical resistance by measurements of weight loss alone, as is most generally done for metals. 

In Fig. 26, we schematically illustrate four stages of failure in epoxies under an increasing tensile load. In each stage we document the craze/crack structure, the stress at the craze/crack surface and the resultant fracture topography. 

Experimental Evidence. Morphology. Figure 3 (33) shows in phase contrast microscopy the development of crack or craze patterns around rubber particles in a toughened polystyrene. The lack of dependence of crack inclination on direction of stress is especially marked in this micrograph, and can be explained only by reference to dynamic branching rather than to crack or craze nucleation by stress raisers. Schmitt and Keskkula refer to the lines as craze cracks and cracks. ... 

Rubber Content. In the theories of toughening where the role of rubber particles is (a) to absorb energy directly or (b) to induce matrix yielding through stress concentration or hydrostatic tension effects, energy absorption should increase linearly with the number of rubber particles (proportional to rubber content if particle size is invariant). On the other hand, if dynamic craze/crack branching is the operative mechanism, evidence of an exponential law may be expected. The exponential form of the law may be derived as follows. 

Crystallinity and disorder are important structural parameters for understanding relationships between structure and physical properties. Flaws and distortions are the main features that limit the ultimate properties of textile fibers. Some of these crazes, cracks and voids are revealed under the electron microscope, either on the surface or in cross sections stained with heavy metals (J, 2). However, these staining techniques (that reveal the main morphological features) make it much more difficult to determine the degree of distortion of the crystalline fraction. Theoretically, line profile studies permit separation of effects due to crystalline size from those due to structural distortions. However, the lack of peaks in semicrystalline fiber x-ray patterns hinders that approach. 

For set B, craze thickening is faster and the craze critical thickness is attained at K / (so r ) 1.32, which is significantly smaller than the value K / (so rt) 1.71 for set A. During crack propagation, some plasticity confined to the craze/crack interface is observed (Fig. 12) but the bulk remains mostly elastic. Therefore, the craze parameters B of Table 3 result in a more brittle response compared to that predicted for the craze parameters A (see Fig. 8b). 

Fig. 16 Craze-crack resistance curves for a constant and a temperature-dependent craze critical thickness...

PC shows either craze or shear behavior, with no mixed behavior, i.e., successively regenerated localized DCG zones. There is a sharp transition between the craze and the shear branches, as seen in Fig. 35. The competition between crazing and shear is temperature and stress sensitive. The mode, once determined, persists as the barrier is high between these two modes. At 75 °C and above, no craze-crack growth is observed, although shear fracture does persist down to —25 °C, albeit only at high stresses. 

Fig. 3. Craze-crack resistance curves for isothermal conditions with = 30 MPav /s and temperature dependent stress-displacement fields for ki = 300 MPa- /m/s and Ki = 3000 MPa- /m/s. The triangle indicates the initiation of crazing while the square corresponds to the onset of unstable crack propagation, defining...

Europium oxide pellets may be exposed to air for several weeks without damage. However, for long-term storage, a dry atmosphere is necessary otherwise, the pellets will craze, crack, and swell by reaction with moisture. ... 

PP is britde, especially at T s T - 0°C. The resin fractures by the crazing-cracking mechanism [Friedrich, 1983]. The discovery of PP immediately followed by search for methods of improvement the low-T impact behavior. PP was blended with EPR or EPDM [Hogan and Banks, 1953, 1955] PE [Holzer and Mehnert, 1963] sPP [Emrick, 1966] aPP [Tanahashi and Kojima, 1970], etc. 

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