Subject tensile deformation

Until now we have restricted ourselves to consideration of simple tensile deformation of the elastomer sample. This deformation is easy to visualize and leads to a manageable mathematical description. This is by no means the only deformation of interest, however. We shall consider only one additional mode of deformation, namely, shear deformation. Figure 3.6 represents an elastomer sample subject to shearing forces. Deformation in the shear mode is the basis... 

As demonstrated in Fig. 11 for material B, most of the tensile deformation was reversible, even at strains of over 40%. In Fig. 11 for each cycle a new sample was employed. In cases where the same specimen had been subjected to repeated load cycling, the authors observed a substantial amount of strain hardening. 

The structural capsules start to be formed in films subjected to deformation in liquids until some tension threshold. Microcracks and microvoids appear and are filled with the inhibiting liquid under tensile stresses exceeding the polymer flow limit. Capillary channels connecting these voids with the process liquid and with each other start to merge or open in the course of structural transformations but do not disappear fully. The liquid may move over the network of the formed channels beyond the polymer matrix limits or concentrate in some voids able under certain conditions to enlarge the manifold. Thermal treatment of the deformed film intensifies the relaxation processes in the polymer matrix, the film shrinks in the tension direction and the capillaries between voids link up densely, thus insulating liquid particles from each other. If the film is treated in the extended state, a more complex mechanism of microcapsule formation is realized [4]. Cl liberation from microcapsules is related to their ability to break spontaneously under residual... 

It can be observed that an infinite channel with a square cross section is obtained from Eq. (10.9) when m oo. Prisms and layered cavities have been used, for example, in structural studies of clays [Joshi et al., 1998 Consolati et al 2002], A discussion of pore-size distributions in low-dielectric thin films [Gidley et al 2000] was based on cubic structures. Of course, other geometries are possible For example, ellipsoidal holes were also considered [Jean and Shi, 1994], in an interesting attempt to frame free-volume holes in semicrystalline polymers subjected to tensile deformation. 

Powers, J. M., and CaddeU, R. M., The macroscopic volume changes of selected polymers subjected to uniform tensile deformation, Polym. Eng. Sci., 12, 432-436 (1972). 

Since the permeability significantly influences the deterioration of concrete, evaluation of water permeability in cracked HPFRCC seans a key factor to describe the durability performance of given materials. Superior impermeability of HPFRCC has been observed by several researchers. Lepech and Li (2005) studied the water permeability of cracked HPFRCC and reinforced mortar specimens. When subjected to identical tensile deformation, the HPFRCC and reinforced mortar specimens exhibited very different cracking patterns and widths. They found that the cracked HPFRCC exhibits nearly the same permeability as sonnd concrete, even when strained in tension to several percent (Figure 6.8). Homma et al. (2009) also evaluated the water permeability of cracked... 

Large plastic deformation can be identified by the accumulation of slips at the macroscopic scale as well as at the atomic scale. During tensile deformation, metal blocks slip on slip planes and rotate, as schematically illustrated in Fig. 1. Increasing plastic deformation results in numerous cross slips. Such slips can be observed as Luders bands in annealed low-carbon steel subjected to tensile deformation. 

The quasi-equilibrium adsorption layers (the formation time of60,000-70,000 sec) were subjected to compressive/tensile deformation sinusoidally in the field of linear viscoelasticity. The dependences of the complex viscoelastic modulus of adsorption layers (E), as well as its elastic (real part. 

It has been shown that the peak positions of the Raman-active bands of carbon fibres are strain-sensitive and that Raman Microscopy can be used to follow the deformation of carbon fibres both in air and in a thermoplastic PEEK matrix. It has been demonstrated that the fibres near the surface in the carbon-fibre/PEEK composite examined are subject to a residual compressive strain of the order of 0.287o which is of the same order as that expected (19) from matrix shrinkage due to crystallisation and thermal contraction on cooling from the processing temperature. It is found that when the composite is subject to an externally-applied tensile deformation then, as expected, the change in fibre strain is similar to the applied strain as expected from simple composite theory. 

Orientation measurements have also been implemented for in-situ analyses of PP. The orientation and relaxation kinetics of melts in shear flows have been studied by IR spectroscopy in a rheometer. In another example, the orientation in the transition front of the neck during tensile deformation has been analyzed by Raman microspectroscopy. This last example is a natural link to studies of samples subjected to mechanical stress. 

Fig. 136. Change in Etf with strain rate at 500 K. for an amorphous La5jAl25Ni2g alloy subjected to tensile deformation at 500 K after the embrittlement treatment by annealing for 1.8ks at450K.

Therefore, let us imagine the adhesive as a set of independent packets of material, each of which is subjected to uniaxial tensile deformation in the direction perpendicular to the substrate surface as shown in Fig. 9. For 90° peel, the... 

The mechanisms of tensile deformation of semicrystalline polymers was a subject of intensive studies in the past [8-20]. It is believed that initially tensile deformation includes straining of molecular chains in the interlamellar amorphous phase which is accompanied by lamellae separation, rotation of lamellar stacks and interlamellar shear. At the yield point, an intensive chain slip in crystals is observed leading to fragmentation but not always to disintegration of lamellae. Fragmentation of lamellae proceeds with deformation and the formation of fibrils is observed for large strains [21-24]. 

We have so far in this section on the yield behaviour of polymers only considered tensile deformation. In order to obtain a complete idea of the yield process it is necessary to know under what conditions yield occurs for any general combination of stresses. For example, glassy polymers are usually brittle in tension when the temperature of testing is sufficiently below Tf, whereas when they are deformed in compression at similar temperatures they can undergo considerable plastic deformation. Also a knowledge of yield behaviour under general stress systems is important in engineering structures where components are subjected to a variety of... 

When the subject of deformation of rubber is considered, a conventional approach such as shear or elongation is accepted. The definition of steady state viscosity is an example of the former and that of tensile testing is an example of the latter. However, the deformation of rubber during mixing is not completely shear nor elongation. Therefore, the way to describe this deformation needs to be examined. The bulk compression need not be considered, because rubber is practically incompressible. 

Machine components ate commonly subjected to loads, and hence stresses, which vary over time. The response of materials to such loading is usually examined by a fatigue test. The cylinder, loaded elastically to a level below that for plastic deformation, is rotated. Thus the axial stress at all locations on the surface alternates between a maximum tensile value and a maximum compressive value. The cylinder is rotated until fracture occurs, or until a large number of cycles is attained, eg, lO. The test is then repeated at a different maximum stress level. The results ate presented as a plot of maximum stress, C, versus number of cycles to fracture. For many steels, there is a maximum stress level below which fracture does not occur called the... 

A Hquid is a material that continues to deform as long as it is subjected to a tensile and/or shear stress. The latter is a force appHed tangentially to the material. In a Hquid, shear stress produces a sliding of one infinitesimal layer over another, resulting in a stack-of-cards type of flow (Fig. 1). 

Whether or not a polymer is rubbery or glass-like depends on the relative values of t and v. If t is much less than v, the orientation time, then in the time available little deformation occurs and the rubber behaves like a solid. This is the case in tests normally carried out with a material such as polystyrene at room temperature where the orientation time has a large value, much greater than the usual time scale of an experiment. On the other hand if t is much greater than there will be time for deformation and the material will be rubbery, as is normally the case with tests carried out on natural rubber at room temperature. It is, however, vital to note the dependence on the time scale of the experiment. Thus a material which shows rubbery behaviour in normal tensile tests could appear to be quite stiff if it were subjected to very high frequency vibrational stresses. 

An important implication of the presence of the shear-extension coupling coefficient is that off-axis (non-principal material direction) tensile loadings for composite materials result in shear deformation in addition to the usual axial extension. This subject is investigated further in Section 2.8. At this point, recognize that Equation (2.97) is a quantification of the foregoing implication for tensile tests and of the qualitative observations made in Section 1.2. 

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