Undeformed polymer solid

Figure 1 (a) Model for the undeformed polymer solid (b) more... 

A more recent hypothesis is that the craze tip breaks up into a series of void fingers by the Taylor meniscus instability - . Such instabilities are commonly observed when two flat plates with a layer of liquid between them are forced apart or when adhesive tape is peeled from a solid substrate jjjg hypothesis in the case of a craze is that a wedge-shaped zone of plastically deformed and strain softened polymer is formed ahead of the craze tip (Fig. 3 a) this deformed polymer constitutes the fluid layer into which the craze tip meniscus propagates whereas the undeformed polymer outside the zone serves as the rigid plates which constrain the fluid. As the finger-like craze tip structure propagates, fibrils... 

At low temperatures (A zone) the polymer is found in the vitreous state. In this state the polymer behave as a rigid solid with low capacity of motions and then the strain is very low. To produce a small strain it is necessary a great stress. Therefore in this zone only specific and local motions take place and the polymer can be considered as undeformable. As the temperature increases (B zone) the glass transition temperature, Tg, is reached and the motions of the different parts of the polymers increases but is not enough to produce important strain. Under this conditions the polymers behave as a rubber. If the temperature remain increasing (C zone) the polymer behave as deformable and elastic rubber but the modulus is small. In this zone the motions of the side chains and also of the main chain increases due to the application of the strain. 

The two main types of behaviour encountered when loading solid polymers are shown in Fig. 7.24. The nominal stress considered is the force per undeformed cross-sectional area. 

This is obviously an oversimplified picture. To handle solidification properly, it is necessary to include an equation that describes the growth of a glassy or crystalline phase and a stress equation that accounts for the biphasic nature of the system. Such descriptions are the subject of recent research, and these results should be used in new simulation codes, especially for semicrystalline polymers, but the approximation of an instantaneous transition from a liquid to an undeformable solid at a fixed average temperature T = Tl captures the important features of the spinline and suffices for our purposes here. 

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