Deformation orientational

This arises when there is a physical ordering of optically anisotropic elements e.g. chemical bonds) along some preferential direction— see Fig. 3. This can occur in polymers by aligning amorphous or crystalline chains as by an extension or drawing deformation. Orientation birefringence is the quantity that is most generally measured (or desired)... 

Finally, though, it should be noted that the studies relating flow deformation, orientation, crystallinity, and strength in the fibre field are the most highly developed of those for any polymer artifacts. They yield many of the starting points for the study of the more complex properties of two dimensional and three dimensional bodies referred to subsequently. 

To take hardening into account, we need to find a quantity that can describe the deformation history of the material. This quantity has to increase during plastic deformation, regardless of the deformation orientation, for, in general, any plastic deformation causes hardening. A frequently used quantity is the so-called equivalent plastic strain To define this strain, we need... 

Since the equivalent plastic strain rate defined this way is positive for all plastic strain rates, the equivalent plastic strain increases for any plastic deformation, regardless of the deformation orientation. 

Chain orientation should not be confused with mechanical strains or frozen-in deformations. Orientation is the result of deformation but a given strain may result in very different degrees of orientation, as the following example illustrates. 

A number of friction studies have been carried out on organic polymers in recent years. Coefficients of friction are for the most part in the normal range, with values about as expected from Eq. XII-5. The detailed results show some serious complications, however. First, n is very dependent on load, as illustrated in Fig. XlI-5, for a copolymer of hexafluoroethylene and hexafluoropropylene [31], and evidently the area of contact is determined more by elastic than by plastic deformation. The difference between static and kinetic coefficients of friction was attributed to transfer of an oriented film of polymer to the steel rider during sliding and to low adhesion between this film and the polymer surface. Tetrafluoroethylene (Telfon) has a low coefficient of friction, around 0.1, and in a detailed study, this lower coefficient and other differences were attributed to the rather smooth molecular profile of the Teflon molecule [32]. 

Fig. 2. The shape-memory process, where Tis temperature, (a) The cycle where the parent phase undergoes a self-accommodating martensite transformation on cooling to the 24 variants of martensite. No macroscopic shape change occurs. The variants coalesce under stress to a single martensite variant, resulting in deformation. Then, upon heating, they revert back to the original austenite crystallographic orientation, and reverse transformation, undergoing complete recovery to complete the cycle, (b) Shape deformation. Strain recovery is typically ca 7%.

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