Uniaxial deformation effects from

The longitudinal effect is the expansion of the crystal in the direction of a uniaxial stress. Following from equation (4.33), the stress g parallel to I is represented by a tensor whose elements are gIJ . The resulting deformation is... 

Diol-modified epoxy resins were prepared from bisphenol A diglycidyl ether modified with alpha,omega-diols of different chain lengths and at different molar ratios, the molecular orientation of the epoxy networks was investigated using rheooptical FTIR spectroscopy and uniaxial deformation was carried out above and below the glass transition temperature. The effects of diol chain length and molar ratio on the mechanical properties and orientation parameter were discussed. 17 refs. 

Klepac extensively studied the effect of uniaxial deformation on the molecular chain segmental mobility of linear low density polyethylene (LLDPE) by ESR spin probe method. The simulated ESR spectra of undeformed and deformed (parallel and perpendicular) LLDPE samples at 0 °C are shown as dotted line in Figure 25.31. The results obtained by simulations indicate that the amount of slow components and corresponding Tr of LLDPE films deformed in both parallel and perpendicular directions are significantly larger than those of the undeformed LLDPE films. However, the amount of fast components decreased in the deformed sample. It was concluded from the results that uniaxial deformation reduces the molecular chain segmental mobility in the amorphous region and increased the amount of crystalline phase of the LLDPE films. 

Triple-shape polymers can change on demand from a first shape (A) to a second shape (B) and from there to a third shape (C), when stimulated by two subsequent temperature increases [10, 26, 27]. Specific cyclic, thermomechanical tensile experiments were developed to characterize the triple-shape effect (Chapter Shape-Memory Polymers and Shape-Changing Polymers [101] and Sect. 2.2) quantitatively. Analogous to the experiments for dual-shape materials, each cycle of these tests consisted of a programming and a recovery module. A cycle started with creating the two temporary shapes (B and A) by a two-step uniaxial deformation, followed by the recovery module, where shape (B) and finally shape (C) were recovered. 

For most practical purposes, the onset of plastic deformation constitutes failure. In an axially loaded part, the yield point is known from testing (see Tables 2-15 through 2-18), and failure prediction is no problem. However, it is often necessary to use uniaxial tensile data to predict yielding due to a multidimensional state of stress. Many failure theories have been developed for this purpose. For elastoplastic materials (steel, aluminum, brass, etc.), the maximum distortion energy theory or von Mises theory is in general application. With this theory the components of stress are combined into a single effective stress, denoted as uniaxial yielding. Tlie ratio of the measure yield stress to the effective stress is known as the factor of safety. 

On the contrary, are(j u/0red clearly shows some dependence on the structure of the crosslinks, changing from around 0.27 to 0.10 as the branching density z increases from 0.01 to 0.5. The different time scale of the experiments can not have effected the results, because is was proved that G is independent of frequency. The deformation ratio X is 1.00005 in case of torsional vibrations and 1.02-1.04 in case of uniaxial extension. Hence it ap-... 

The effects of orientation on the mechanical properties of polymers at both small and large deformations depend on the mode of orientation, which determines the preferred average chain alignment. For example, the mechanical properties obtained after uniaxial orientation (which biases the chain end-to-end vectors in one favored direction) differ from those obtained by biaxial orientation (which biases these vectors in two favored direction). Furthermore, the mechanical properties obtained after simultaneous equibiaxial orientation (where orientation in the two favored directions is imposed simultaneously, at equal rates, and to equal extents) often differ from those obtained after sequential orientation in the two favored directions, as well as after orientation by different amounts and/or at different rates in those two directions. See Seitz [35] for a review of the effects of uniaxial and biaxial orientation on the fracture of polystyrene, which fails by brittle fracture or crazing, under uniaxial tension and impact. 

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