Defects fringe patterns

Fig. 16. The fringe pattern evolution for the case of a crack growing into an immobile craze. Note the defect shown by the star that proves the craze tip does not move. From Ref. courtesy of Chapman and Hall, Ltd.

Crystals oriented to satisfy Bragg s law are used as optical components in X-ray interferometry. The interference patterns are sufficiently sensitive to small displacements to allow the observation of strains and defects in crystals. Lattice rotations of 10 rad or dilations dd/d of 10 can be detected. Inhomogeneous strain produces moire fringe patterns showing dislocations and the strain-associated impurities in concentrations below one in 10 . 

Fig.4 Fig.6 are optical experiment results of photo-elasticity of regular PS plates described in Fig. 1 and Fig.2. From a series of multicolored band or fringed pattern, it shows that different processing conditions have different residual stress results. When melt temperature becomes higher, multicolored band or fringed pattern is also change and the multicolored band is wider (Fig 4). In Fig.5, packing pressure increases, the fringe band becomes narrow. There seems no change in Fig.6 while injection speed is increased. To discuss if parts defects have effects on residual stress and optical performance, short-shot PS plates are also measured, the results are shown in Fig.7.

Fig.7 is the photoelastic experimental results for short-shot PS part. Compared Fig.7 with Fig.5, it can be seen that photoelastic interference fringe pattern is different, and the former has more interference fringes than the latter, that is the defect parts have poorer inner qualities. 

A second important event was the development by Hosemann (1950) of a theory by which the X-ray patterns are explained in a completely different way, namely, in terms of statistical disorder. In this concept, the paracrystallinity model (Fig. 2.11), the so-called amorphous regions appear to be the same as small defect sites. A randomised amorphous phase is not required to explain polymer behaviour. Several phenomena, such as creep, recrystallisation and fracture, are better explained by motions of dislocations (as in solid state physics) than by the traditional fringed micelle model. 

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