Van der Waals crazing

Fig. 17. A plot of the ratio r of the initial crazing stress to the crazing stress for van-der-Waals crazing as a function of temperature for PS having a molecular weight of 260,000 ( ) and 1,150,000(0). The jo/fd carve corresponds to the prediction based on the craze growth model (using Eq. (20)) and a value of V = 6,7 nm s" ...

The results of Plummer and Donald also clearly show qualitatively the strain rate dependent behavior to be expectal from the model. Figure 22 shows their results for PES strained at a rate of 1 x 10 s contrasted with their results at a much slower rate of 6x 10 s F The critical strain for shear deformation and the critical strain for van-der-Waals crazing both increase with the increase in strain... 

In the high temperature, van-der-Waals regime the X s in PS crazes (and presumably those in the PES and PC crazes also) depend on the craze interface... 

The fracture resistance of a thermoplastic depends critical upon its relative molar mass, essential because Gjc and fall rapidfy when the chains are too short to form effective entanglements. This point is illustrated in Figure 5.19. Very short chains are held tt ther oi by van der Waals forces, and are unable to form stable crazes. 

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