Modes of Segmental Deformation

From Table 5.3 it is apparent that the weakest mode of skeleton deformation (4.7 GN/m ) is that derived from the hindered rotation of (non-extended) bonds whereas a fully extended chain segment has a 50 times larger stiffness. The elastic modulus of a partially extended kinked chain, then, is ... 

Seymour et al. [363] also studied the segmental orientation of MDI based PUs during deformation using differential IR dichroism. The NH, CH and bonded and free C=0 peaks were used to determine the degree and direction of orientation of the HS and SS. They found that the mode of the HS orientation was strongly dependent on the type of ordering present within the hard domains. In the case of materials derived from crystalline hard domains, the orientation of the HS at low strains was shown to be transverse to the direction of stress. Similar observations were made by us for materials based on the diisocyanate DBDI crystallizing, especially when obtained with diol chain extenders like EG or BG [67]. 

The two modes of macro-cracking that occur in bending tests in case of large specimen deformation with attached TBC are shown in Fig. 2. With the TBC under tension almost equidistant segmentation cracks develop (Fig. 2a). The ratio of crack distance to TBC thickness is about E k, 2.25 which is in fair agreement with... 

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