Some fatigue characteristics of thermoplastics

Crawford, R. J.; Benham, P. P.

doi:10.1016/0032-3861(75)90212-8

Cited by 68 publications

(43 citation statements)

References 9 publications

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“…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.…”

Section: Effect Of Frequencymentioning

confidence: 76%

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

2008

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A method is presented that allows fatigue life predictions on the basis of creep life data. The approach is based on the assumption that the time-dependent failure of polymers is determined by the intrinsic strain softening that is initiated when a critical threshold value of the plastic strain is surpassed. To facilitate fatigue predictions, an acceleration factor is defined that indicates how much faster plastic strain is accumulated by a cyclic signal compared to its static mean stress. Analytical solutions of the acceleration factor are presented for triangular and square waves, which predict that only the stress amplitude of the cyclic signal and the material's stress dependency affect fatigue life, whereas frequency plays no role. Verification using several glassy and semicrystalline polymers demonstrates that this method yields accurate quantitative lifetime predictions not only for polymers that exhibit ductile failure but also for those that display brittle fracture, provided that fracture is preceded by (localized) plastic flow.

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Section: Effect Of Frequencymentioning

confidence: 76%

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

2008

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“…The initial strain amplitude at a slightly lower max of 57 MPa, was 0.93%. This critical max value was employed to divide the response of PA6 into low-stress and high-stress regimes, as this has been previously reported for several other similar material systems (2,18,22). Although the critical max is higher for PA6NC than for PA6, the relative stress value with respect to the UTS and also the initial strain amplitude at which this transition occurs are very similar.…”

Section: Axial Fatiguementioning

confidence: 92%

“…In the high-stress regime, the temperature rose just before necking, suggesting the occurrence of the wellknown thermal instability phenomenon (2,18), caused by poor dissipation of the heat generated by viscoelastic damping. However, experiments employing a trapezoidal cyclic waveform with varying hold times at maximum and minimum stresses showed that the thermal instability was controlled by a threshold value of the accumulated strain in the specimen rather than by the testing frequency (23).…”

Section: Axial Fatiguementioning

confidence: 99%

“…Strain monitoring during fatigue of a PA6-based nanocomposite has previously been reported (15,16); however, attention was drawn primarily to the thermal instability phenomenon. This phenomenon results from cycling a large volume of material above a critical stress amplitude or loading frequency leading to hysteretic heating (17,18). In a previous paper (19), the effect of nanoparticles on the evolution of bulk fatigue damage has been reported.…”

Section: Introductionmentioning

confidence: 99%

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Fatigue crack initiation and propagation in polyamide‐6 and in polyamide‐6 nanocomposites

et al. 2004

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Recent developments in polymer nanocomposites have led to improvements in conventional short‐term, but the long‐term mechanical properties have received little attention. The objective of the present study was to characterize the effect of nanoparticles on the fatigue crack initiation and propagation mechanisms and on the fatigue properties of polyamide‐6 (PA6) nanocomposite (PA6NC) prepared by in situ polymerization with montmorillonite clay. Two approaches were employed: fatigue life measurements and crack growth monitoring. Compared with non‐filled PA6 at the same stress amplitude, the number of cycles to fracture was higher for the nanocomposite, which suggests an increase in the intrinsic resistance of the material to crack initiation. However, the crack growth rate results indicated that nanoparticles decreased the resistance to crack propagation. Post‐fatigue fractographic observations indicated a change in the fatigue crack propagation mechanism resulting from the addition of nanoparticles, primarily attributed to the increase in yield stress, which favors the development of a fibrillated deformation zone. The fibrillation process in the relatively high crack propagation rate regime appeared to be preceded by plastic deformation at approximately constant volume. Most of the effect of nanoparticles on the fatigue behavior and properties results probably from the mechanical reinforcement on the microstructure and its effect on the yield stress and Young's modulus rather than from the effect of the inorganic filler to act as a stress concentrator. Polym. Compos. 25:433–441, 2004. © 2004 Society of Plastics Engineers.

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“…For such fatigue testing parameters, two distinct fracture mechanisms are generally observed in polymers [24,35,36]. Above a certain level of cyclic load or above a certain loading frequency, an unstable increase of the specimen temperature induces a thermally-dominated fatigue fracture.…”

Section: Fatigue Testingmentioning

confidence: 99%

Bulk fatigue damage evolution in polyamide-6 and in a polyamide-6 nanocomposite

et al. 2005

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The mechanical response of a polyamide‐6 montmorillonite clay nanocomposite and of a polyamide‐6 was monitored during axial fatigue tests performed at R‐ratios of 0.1 and −1. For both materials, two transitions were usually observed in the evolution of all the stress‐strain‐time parameters studied after similar numbers of loading cycles, suggesting interrelationships between the mechanisms of molecular reorganization. Fatigue test monitoring indicated an initial decrease in the storage modulus and a subsequent trend for this modulus to increase, especially in polyamide‐6. During all tests, a partially recoverable strain was accumulated because of viscoelastic deformation. Nanoparticles reduced this strain in the initial cyclic straining regime but not in the last regime, probably because such particles cannot inhibit viscoelastic events constrained in a volume larger than their interaction volume within the matrix. Based on the accumulated volume variation measured, the nucleation and growth of microvoids can be expected to occur in the last cyclic straining regime. POLYM. COMPOS., 26:636–646, 2005. © 2005 Society of Plastics Engineers

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Some fatigue characteristics of thermoplastics

Cited by 68 publications

References 9 publications

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

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

Fatigue crack initiation and propagation in polyamide‐6 and in polyamide‐6 nanocomposites

Bulk fatigue damage evolution in polyamide-6 and in a polyamide-6 nanocomposite

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