Fatigue and Cyclic Thermal Softening of Thermoplastics

Abstract

Thermoplastic components subjected to cyclic loading may distort because of localized rises in temperature and/or fracture because of incremental (fatigue) crack propagation from microscopic cracks or defects produced during the manufacturing process or by service conditions. The object of the present paper is to show quantitatively how the first mode of failure, which is referred to as cyclic thermal softening, can be related to loss compliance, specimen geometry and the frequency and magnitude of the cyclic load. The results of cyclic bending tests on polymethylmethacrylate (p.m.m.a.) and Polyvinylchloride (p.v.c.) beams of rectangular and circular cross-section are analysed. For the service conditions considered the p.m.m.a. specimens showed both failure modes whereas the p.v.c. specimens failed as a result of incremental (fatigue) crack propagation.

An Analytical Method To Predict Fatigue Life of Thermoplastics in Uniaxial Loading: Sensitivity to Wave Type, Frequency, and Stress Amplitude

“…24,27 The frequency applied also appears to have an effect on the time-to-failure of the signal with a stress amplitude of 10 MPa, in particular at higher frequencies (see Figure 16a). It is well-established that polymers dissipate a substantial amount of energy at high stress [48][49][50][51][52][53] and high frequency, [53][54][55][56] which causes substantial heating of the sample as also demonstrated in ref 13. For that reason, a frequency dependence may be anticipated at higher amplitudes, where hysteretic heating is more likely to occur.…”

Dynamic flow and failure of confined polymethylmethacrylate

“…Here, an additional component of the problem is the nature and extent of thermomechanical coupling effects in which the mechanical energy transforms readily at low frequencies into thermal energy. This causes self-heating of the material (Constable et al, 1970;Rittel, 2000b). When the strain rate becomes higher, as in the case of impact, the thermomechanical problem becomes dominant, since very high (homologous) temperatures are likely to develop (Rittel, 1999).…”

Morphological study of fatigue-induced damage in isotactic polypropylene

“…1,2 At high frequencies and/or stress levels, the fatigue life of the polymer is dominated by hysteretic heating. This occurs as a consequence of the high internal damping and low thermal conductivity inherent in many polymers.…”