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Large-strain cyclic deformation

In a previous article (2) we described a new approach to the analysis of nonlinear viscoelasticity as encountered in such large-strain cyclic deformation of polymers. In this chapter, we describe the apparatus used and the method of treating the data obtained. [Pg.36]

The term dynamic test is used here to describe the type of mechanical test in which the rubber is subjected to a cyclic deformation pattern from which the stress strain behaviour is calculated. It does not include cyclic tests in which the main objective is to fatigue the rubber, as these are considered in Chapter 12. Dynamic properties are important in a large number of engineering applications of rubber including springs and dampers and are generally much more useful from a design point of view than the results of many of the simpler static tests considered in Chapter 8. Nevertheless, they are even today very much less used than the "static" tests, principally because of the increased complexity and apparatus cost. [Pg.173]

The application of this normalized, relative stress in Eq. (32) is essential for a constitutive formulation of cyclic cluster breakdown and re-aggregation during stress-strain cycles. It implies that the clusters are stretched in spatial directions with deu/dt>0, only, since AjII>0 holds due to the norm in Eq. (33). In the compression directions with ds /dt<0 re-aggregation of the filler particles takes place and the clusters are not deformed. An analytical model for the large strain non-linear behavior of the nominal stress oRjU(eu) of the rubber matrix will be considered in the next section. [Pg.62]

According to these considerations, we assume that for quasi-static, cyclic deformations of filler reinforced rubbers up to large strain the total free energy density consists of two contributions ... [Pg.63]

Measurement of Nonlinear Viscoelastic Properties of Polymers in Cyclic Deformation under a Relatively Large Strain Amplitude... [Pg.35]

Another problem which arises in a cyclic deformation under a large strain amplitude is that the modulus of material varies significantly during a cycle because of strain-stiffening or strain-loosening effects. Therefore, analysis of the viscoelastic properties in this case must include the variation of modulus during a cycle. [Pg.37]

In dynamic tests the rubber is subjected to cyclic deformation, and the stress and strain are monitored. Dynamic properties are important in a large number of engineering applications of rubber, including springs and dampers, and are generally much more useful from a design point of view than the results given by the static tests. [Pg.143]

At low plastic strain amplitudes (ACp/ 2<2xl0 ), the deformation is mainly accommodated by the softer austenitic phase of the duplex alloy. Movement of the screw dislocations in the a-phase is very difficult because of the low temperature behavior of this phase at 300 K. Cyclic deformation of the austenitic phase then controls the fatigue properties of the duplex alloy. Because of the large reversibility of the cyclic strain, delayed transgranular crack initiation occurs in this phase (Fig. 5-34a). This explains the good fatigue resistance of the two-phase alloy at Agp/2< 10" as shown in the Coffin-Manson curve (Fig. 5-33). [Pg.234]

The viscoelastic response of polymer melts, that is, Eq. 3.1-19 or 3.1-20, become nonlinear beyond a level of strain y0, specific to their macromolecular structure and the temperature used. Beyond this strain limit of linear viscoelastic response, if, if, and rj become functions of the applied strain. In other words, although the applied deformations are cyclic, large amplitudes take the macromolecular, coiled, and entangled structure far away from equilibrium. In the linear viscoelastic range, on the other hand, the frequency (and temperature) dependence of if, rf, and rj is indicative of the specific macromolecular structure, responding to only small perturbations away from equilibrium. Thus, these dynamic rheological properties, as well as the commonly used dynamic moduli... [Pg.89]

Figure 3.19. Cyclic stress-strain behavior of HiPS (Bucknall, 1967 ) Note the development of a second yield stress after the first deformation cycle, and the large increase in hysteresis. Figure 3.19. Cyclic stress-strain behavior of HiPS (Bucknall, 1967 ) Note the development of a second yield stress after the first deformation cycle, and the large increase in hysteresis.
In addition, PLCL scaffolds can be easily twisted and bent. In contrast, PLGA scaffolds largely deform and are broken even at strains as low as 20%. These data indicate that PLCL scaffolds are flexible and highly elastic, whereas PLGA scaffolds are stiff and brittle. To further examine the elastic properties of PLCL scaffolds, scaffolds with varying porosity were subjected to cyclic strain at 10% amplitude and 1 Hz frequency for 27 days in culture medium (Jeong, 2004b). PLCL scaffolds of all tested porosities maintained excellent elasticity even in the hydrolytic medium over a 27-day experimental period. [Pg.100]

The creation of the triple-shape capability for an AB polymer network system by a simple one-step process similar to a conventional dual-shape progranuning process was shown for networks based on PCL and PCHMA [24] (see Sect. 2.4). In these materials a stress-controlled cyclic, thermomechanical experiment was used to quantify the triple-shape effect. The sample was deformed at 150°C (liigh) to 50% (Ein) and subsequently cooled to —10°C (Tio ). The large temperature interval of around 160 K led to a strong reduction of the strain. When the sample was heated... [Pg.131]

Thus, as indicated above, in the submicron-sized 3Y-TZP ceramic, the stress-induced cyclic hardening, due to transformation taking place, was higher than under static deformation. NanocrystaUine 3Y-TZP softened cyclically, due to the formation of a large number of microcracks. In the submicron structures, this observation basically reflects the effects of dislocations and dislocation-dislocation interactions. In the nanocrystalline 3Y-TZP ceramic, this greater ability to accommodate plastic strain is probably due to grain-boundary sliding, since in nanocrystalline structures dislocations cannot move, because shp distances are on an atomic scale (hke the dimensions of dislocations themselves). [Pg.568]

At a small number of cycles (lcf), the stresses are large and the total strain is mainly determined by plastic deformation. In the LCF regime, a good approximation for the relation between plastic strain amplitude and cyclic life is given by the Coffin-Manson equation [32,94,95]. [Pg.361]


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