Crazing crack growth

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. 

ESC, described in Section 4.9.4, is a physical phenomenon and is the acceleration of stress cracking by contact with a fluid, i.e., stress cracking will occur without the fluid at sufficiently long times. Ultimately, the slow crack growth that follows crazing reaches a critical point when fast crack growth and failure occurs. This failure, with or without the accelerating effect of a fluid, is a creep rupture effect (see Section 8.12). 

Failure stage Coarse craze Slow crack growth Slow crack growth Fast unstable... 

Locally Heterogeneous Deformation Crazing and Slow Crack Growth. .. 22... 

Fig. 11 Craze in commercial polystyrene showing the characteristic steps nucleation through void formation in a pre-craze zone, growth of the fibrillar structure of the widening craze by drawing-in of new matrix material in the process zone, and final breakdown of the fibrillar matter transforming a craze into a crack (the crack front is more advanced in the center of the specimen, shielded by a curtain of unbroken fibrils marked by the arrow). The fibril thickness depends—of course—on the molecular variables, the strain rate-stress-temperature regime of the crazing sample and on its treatment (preparation, annealing) and geometry (solid, thin film) for PS typical values of between 2.5 and 30 nm are found [1,60,61]...

Investigation of the crack tip of PMMA after a stable crack growth reveals that, at room temperature, a single craze is present. 

Based on our observation, a membrane degradation and failure mechanism under the RH cycling, a pure mechanical effect is theorized as the following sequence electrode-microcracking- - crazing initiation at the electrode/electrolyte interface - crack growth under stress cycling- -fast fracture/instability. 

Lagaron JM, Capaccio G, Rose LJ, Kip BJ (2000) Craze morphology and molecular orientation in the slow crack growth failure of polyethylene. J Appl Polym Sci 77(2) 283—296... 

The aim of this review is to concentrate mainly on these fundamental aspects of the fracture behavior of glassy thermoplastics. In the first Section, following an outline of the relevant fracture mechanics theory, the optical interference method is described and the nature of the results obtainable from it is discussed. The next Section then considers the behavior of cracks and crazes in specimens subjected to quasistatic loading, whilst the final Section examines the role of crazing associated with fatigue crack growth. 

Fig. 42. Schematic representation of correlation between loading phase with crack propagation, craze growth and striation formation during continuous crack growth (in PMMA)...

A deeper insight into the growth behavior of the craze zone at the crack tip during retarded crack growth in PVC has been obtained by recent optical interference measurements on which the following is mainly based. Figure 49 is an... 

Fig. 51. Schematic representation of optical interference results of continuous craze and discontinuous crack growth in PVC...

Continuous craze growth has to be seen in relation to the discontinuous crack growth looking at a finer scale e.g. at one loading cycle then discontinuous craze growth is to be expected. 

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