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Deformation cycling

The forced vibration methods away from resonance can again be subdivided into those which apply deformation cycles and those which apply force cycles, the more usual being deformation cycles. An alternative form of test uses transient loading instead to continuous cycling. [Pg.192]

Any rubber test piece with or without added mass has a natural or resonant frequency of vibration determined by the dimensions and viscoelastic properties of the rubber, the total inertia of the system, and the mode of deformation. If constant force amplitude cycles are applied to the rubber and the frequency varied, the resulting deformation cycles will have a maximum value when the applied frequency equals the resonant frequency of the test piece system. [Pg.195]

Flexometers or heat build-up fatigue apparatus operate in compression, shear or a combination of the two and various designs have been in use and standardised, particularly by ASTM, for many years. The test piece geometry and deformation cycle used are, inevitably, somewhat arbitrary and this perhaps contributed to it being much later before there was an international or British standard method. [Pg.254]

Fatigue is the decay of mechanical properties after repeated application of stress and strain. Fatigue tests given information about the ability of a material to resist the development of cracks or crazes resulting from a large number of deformation cycles. [Pg.882]

The strain response can be broken down into its elemental components of stress, which are in phase or out of phase, to derive the values for G and G". The storage modulus G is the ratio of the applied stress that is in phase with the strain (8 = 0°). This means that G is an expression of the magnitude of the energy stored in the material, recoverable per deformation cycle (68). The loss modulus G" is the ratio of the applied stress that is out of phase with the strain (8 = 90°), meaning that it is a measurement of the energy lost as viscous dissipation per deformation cycle (66-68). These two moduli are dependent on the phase angle of the system and are... [Pg.193]

The same PEE material was used for this study as in the previous sections. Using a stretching device it was possible to perform measurements up to 70% overall relative deformation s at which point the sample broke. Again the deformation was increased in steps of 5%. The main difference was that in previous studies (Sections 6.2.1-6.2.3) the deformation was increased continuously without relaxation, whereas in this case the sample was unloaded and allowed to relax after each H measurement under stress before the next H measurement without stress (a = 0) was performed. The sample was then stretched to the next deformation and H was measured again. It should be noted that beyond some overall deformation (typically s > 20%) the unstressed sample shows some residual (plastic) deformation amounting about 50% of the strain s under stress. The same deformation cycle has been used for SAXS measurements aimed at the morphological characterization of these PEE samples. [Pg.199]

A key difference between the step-scan FT-IR and PA-IR approaches to DIRLD is the shortest achievable acquisition time. The PA-IR experiment only requires, in principle, a single deformation cycle. On the other hand, at least one deformation cycle must be applied for each of the 512 steps required to generate a typical step-scan FT-IR spectrum with a 2000cm bandwidth and an 8cm resolution. In practice, several cycles must normally be averaged to obtain an acceptable SNR because of the very weak DIRLD signal (see the y-axis scale of Figure 13.9). [Pg.443]

The results from the in situ X-ray study of propylene-based ethylene-propylene copolymer during tensile deformation (36) are described as follows, because the deduced molecular mechanism appears to be universal in all elastomeric polyolefin copolymers. The stress-strain curves and selected WAXD patterns during extension up to strain 5.0 and subsequent retraction back to strain 1.7 (i.e., at zero stress) in the first deformation cycle are shown in Fig. 8.22. [Pg.215]

In contrast, in the case of the contact deformation displacement of ball-to-flat counterformal contacts discussed above no effect of adhesion was found as compared with the influence of the (bulk) viscoelastic properties of the materials. (This may be due to elastic relief forces which may burst adhesive junctions during the loadingunloading contact deformation cycles.)... [Pg.21]

Slight attachment of the transferred particles to the metal allows a conclusion that inhibition of oxidation (Neozone) and relaxation (anthracene) of the HD PE transfer fragments macromolecules decrease the number of macroradicals capable of strong attachment to the steel surface. Transfer fragments undergo fewer deformation cycles and faster become wear debris. The molecular features of the above fragments have been found to correlate or to be superior to those of the original HD PE ( Fig. 2, curves 1, 3, and 4 ). [Pg.211]

Figure 9. Dependence of plastic deformation on deformation amplitude as a function of the number of deformation cycles. Figure 9. Dependence of plastic deformation on deformation amplitude as a function of the number of deformation cycles.
Figure 10. Effect of number of uniaxial deformation cycles (Ae = 50%) on photooxidation as a function of UV exposure time. Figure 10. Effect of number of uniaxial deformation cycles (Ae = 50%) on photooxidation as a function of UV exposure time.
Because the manner of breakdown and the rate at which it occurs in a fatigue test depend on so many factors, notably the mode of stressing, whether stress or strain cycles are used, the frequency, the shape of the deformation cycle (c.g.. smooth sinusoid or sharp pulse), and the environment, it is clear that a single test can only relate to the actual conditions used. One of the problems with the traditional standard tests is that the results are specific to the particular conditions, and these are arbitrary. [Pg.246]

Since fatigue failure of rubber is envisioned as growth of intrinsic flaws, measurement of fatigue lifetimes (e.g., deformation cycles to failure) can provide a measure of the intrinsic flaw size (Gent et al., 1964 Lake andLindley, 1965 Lake, 1983). Table 3.4 includes the flaw sizes determined from the fatigue life of these sample NR compounds (Choi and Roland, 1996). [Pg.158]

At some compositions and under some hydrolysis conditions, bicontinuous phases can be obtained (with the silica and polymer phases interpenetrating one another). The mechanism may be spinodal decomposition, occuning either before or after the polymerization. Since the two networks interpenetrate one another, the mechanical properties first exhibited by the material can be very peculiar. In a first deformation, the silica network would give a very high initial modulus, but once this structure is broken, additional deformation cycles would indicate much lower values of the modulus. [Pg.406]

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.
One-way effect the effect that the material remembers to return to its original shape when heated, but the material needs external loads to make it deform. This thermally driven deformation cycle is the basis for most SMA microvalves. [Pg.3295]

The decrease of deformation that immediately follows the first extension at the higher rate does not exactly lead to initial state indeed, in the short time of the dynamic deformation cycle, adsorption can not reach equilibrium state and remains imperfect, as illustrated by state . [Pg.390]

Table 4. Fabric bursting strength and strain and relaxation, creep and bagginess afbr five deformation cycles at 75 N... Table 4. Fabric bursting strength and strain and relaxation, creep and bagginess afbr five deformation cycles at 75 N...
The mechanical hysteresis of a PU investigated by Gorce based on MDl/BDO and PTMO of molar 2 000 g/mol was also found to be sensitive to the temperature-dependent morphologies of this material and to the morphological changes induced by the strain level and deformation energy during a deformation cycle [291]. [Pg.209]


See other pages where Deformation cycling is mentioned: [Pg.42]    [Pg.477]    [Pg.617]    [Pg.622]    [Pg.245]    [Pg.296]    [Pg.6]    [Pg.8]    [Pg.64]    [Pg.70]    [Pg.81]    [Pg.411]    [Pg.27]    [Pg.37]    [Pg.41]    [Pg.390]    [Pg.443]    [Pg.110]    [Pg.102]    [Pg.324]    [Pg.407]    [Pg.346]    [Pg.184]    [Pg.605]    [Pg.603]    [Pg.118]    [Pg.209]   
See also in sourсe #XX -- [ Pg.572 ]




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