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Fatigue hysteretic heating

Constant deflection amplitude fatigue testing is probably the less demanding of the two techniques, because any decay in the modulus of elasticity of the material due to hysteretic heating would lead to lower material stress at the fixed maximum specimen deflection. In the constant load amplitude tests, maximum material stress is fixed, regardless of any decay in the modulus of elasticity of the material. [Pg.84]

At a low frequency and low stress level, the temperature inside the polymer specimen will rise and eventually reach thermal equilibrium when the heat generated by hysteretic heating equals the heat removed from the specimen by conduction. As the frequency is increased, viscous heat is generated faster, causing the temperature to rise even further. After thermal equilibrium has been reached, a specimen eventually fails by conventional brittle fatigue, assuming the stress is above the endurance limit. However, if the frequency or stress level is increased even further, the temperature will rise to the point that the test specimen softens and ruptures before reaching thermal equilibrium. [Pg.105]

Opp and co-workers (14) attempted to extend the universal slopes equation to predict the behavior of polymer fatigue. However, in their attempts they showed that a form of equation 6 was not useful for predicting polymer behavior and instead developed a model to predict the low cycle fatigue behavior based on hysteretic heating. And in this sense is consistent with those presented in equation 3 and References 15-17. [Pg.3052]

The temperature of the specimen is monitored while testing as the specimen may heat up during the test. This process is referred to as hysteretic heating. Temperature is measured at the surface either by thermocouples that are attached to the surface or by noncontact infrared thermometers. Fig. 1.21 and Table 1.1 show examples of heating in polytetrafluo-roethylene (PTFE) during fatigue testing. [Pg.10]

Semicrystalline Polymers. As a class, semicrystalline polymers tend to exhibit superior fatigue resistance, relative to that of amorphous polymers, both in terms of a-N behavior and FCP rates (2,4,169), as long as tests are conducted at frequencies low enough to minimize excessive hysteretic heating. This is so, even allowing for variations, due to molecular weight. Indeed even though performance in a standard S-N test at 30 Hz may be relatively ppor, many such... [Pg.458]


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