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

Janssen, Rpm Roel; Govaert, Leon Le; Meijer, Heh Han

doi:10.1021/ma071274a

Cited by 55 publications

(55 citation statements)

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“…According to this result the acceleration factor for the triangular signal is independent of the frequency of the stress signal, which is consistent with the experimental data of Janssen et al [53]. The equivalent plastic strain rate for a dynamic stress signal can be calculated by multiplying Equation (2.10) with Equation (2.1), resulting in the dashed line in Figure 2.8 (right).…”

Section: Figure 28 Left: Schematic Representation Of a Triangular Wasupporting

confidence: 89%

“…Therefore, the solution for the time-to-failure as found for constant loads (Equation (2.8)) cannot be employed directly for a dynamic load. An acceleration factor for the deformation kinetics (a d,γ ) similar to the one proposed by Janssen et al [53], is applied to circumvent a numerical procedure to find the failure time for dynamic stress signals. The acceleration factor is defined as the accumulated plastic strain after one triangular stress cycle (excluding physical ageing effects), divided by accumulated plastic strain for a constant stress with a value equal to 1 4f…”

Section: Modelling Dynamic Fatigue Failurementioning

confidence: 99%

“…The solution for a triangular and a square wave of this acceleration factor is deducted in the appendix of [53]. For a triangular waveform the solution is given by:…”

Section: Figure 28 Left: Schematic Representation Of a Triangular Wamentioning

confidence: 99%

“…Janssen et al [53] already provided a solution for the acceleration factor of the deformation kinetics for a triangular wave (in tension) and with the approximation that sinh(x) ≈ 0.5 · exp(x) for x ≫ 1.…”

Section: B Appendix: Analytical Solution For a Triangular Waveformmentioning

confidence: 99%

“…Within the last twenty years major steps forward were achieved using three dimensional constitutive relations [48][49][50][51][52][53][54][55][56]. These models enabled accurate prediction of deformation and strain localisation phenomena in glassy polymers [57][58][59], revealing the crucial role of intrinsic post-yield characteristics in strain localisation behaviour.…”

Section: Introductionmentioning

confidence: 99%

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Residual lifetime assessment of uPVC gas pipes

Visser¹

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Klis (www.loekvanderklis.com) and are used with permission. RESIDUAL LIFETIME ASSESSMENT OF UPVC GAS PIPES PROEFSCHRIFT SummaryThe Dutch gas distribution network consists of about 20% (22,500 km) of unplasticised poly(vinyl chloride) (uPVC) pipes, most of which have been installed from the mid-sixties up to the mid-seventies of the previous century and have been in service ever since. In the next decade the specified service lifetime of 50 years will be reached for these pipes. Replacing the uPVC gas pipes exactly after this specified service lifetime will lead to a costly and extremely labour intensive project. Postponing the replacement is only an option when this can be done without compromising the integrity of the network. It is therefore of great value for the network operators to have full knowledge on the condition of the pipes in their network. In this thesis the framework for a method that can determine the condition, and therewith the residual lifetime, of uPVC gas pipes is developed.Recent failure data shows that the majority of the failures in uPVC gas pipes is caused by excavation activities (third-party damage). The risk of life threatening situations after such a failure is considerably higher for a brittle fracture than for ductile failure behaviour of the pipe. Brittle uPVC gas pipes should therefore be replaced, which makes the impact behaviour the limiting factor for the service lifetime of these pipes. A review of the degradation mechanisms occurring during the lifetime of uPVC pipes shows that physical ageing is expected to be the most important mechanism that causes embrittlement. During physical ageing the polymer chains move towards their thermodynamically favoured positions, causing an increase in resistance against plastic deformation. Moreover the deformation behaviour localises, causing embrittlement on a macroscopic scale. The focus of this thesis is therefore on the influence of physical ageing on the mechanical behaviour of uPVC gas pipes. The procedure of determining the residual lifetime is based on these findings and is split into four aspects: the choice of a measure for the condition of the pipe material, characterisation of the change of the condition in time (its ageing kinetics), determining the critical condition and development of a method of measuring the current condition. Each of these aspects is individually described in consecutive chapters. i ii SummaryThe yield behaviour is selected as the measure for the condition of uPVC gas pipes, as the yield stress is a direct measure for the thermodynamic state (i.e. the age) and can also be linked to the impact behaviour of the material. The yield stress behaviour of uPVC is characterised using short-term tensile tests (at a wide range of strain rates and temperatures) in Chapter 1. The yield behaviour is accurately described by a pressure-modified Eyring relation that links the applied deformation rate to the yield stress and, vice versa, the applied stress to the plastic deformation rate. By hypothesising that failure...

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Section: Figure 28 Left: Schematic Representation Of a Triangular Wasupporting

confidence: 89%

Section: Modelling Dynamic Fatigue Failurementioning

confidence: 99%

“…The solution for a triangular and a square wave of this acceleration factor is deducted in the appendix of [53]. For a triangular waveform the solution is given by:…”

Section: Figure 28 Left: Schematic Representation Of a Triangular Wamentioning

confidence: 99%

Section: B Appendix: Analytical Solution For a Triangular Waveformmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Residual lifetime assessment of uPVC gas pipes

Visser¹

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Influence of fiber orientation, temperature and relative humidity on the long‐term performance of short glass fiber reinforced polyamide 6

Pastukhov

Kanters

Engels

et al. 2020

J of Applied Polymer Sci

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As a result of processing of short fiber reinforced thermoplastics, the fiber orientation varies throughout a product giving rise to a pronounced anisotropic mechanical response. Different flow conditions in a product result in spatial variation in both short‐ and long‐term mechanical properties. In this study, a modeling approach is presented to evaluate the lifetime of short fiber reinforced polyamide 6, both in plasticity‐ and crack growth controlled regions of failure. In the plasticity‐controlled region, a viscoplastic model based on separation of the load angle (by means of Hill's equivalent stress formulation) and time dependence of the yield stress is used in the form of an associative flow rule. The influence of temperature and relative humidity on the magnitude of the plastic flow rate is described by using an apparent temperature approach combined with a Ree‐Eyring formulation. The depression of the glass transition temperature in the polyamide 6 matrix with increasing amount of absorbed moisture was used to predict the anisotropic deformation kinetics in a humid environment. Similar to the plasticity controlled failure, in slow crack growth controlled failure region the effect of temperature, relative humidity, and load angle on the lifetime under a fatigue load is investigated. The apparent temperature approach could also be successfully applied to predict the slow crack growth failure, while the load angle dependence is shown to scale similar to the plasticity‐controlled failure with the Hill's equivalent stress.

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Time‐dependent failure of off‐axis loaded unidirectional glass/iPP composites

Erartsın

Amiri-Rad

Drongelen

et al. 2022

J of Applied Polymer Sci

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In our previous study, we demonstrated that the time‐dependent failure of transversely loaded UD (unidirectional) glass/iPP is fully plasticity‐controlled and proposed a lifetime prediction method based on plasticity to predict transverse failure. In the present work, extending our previous study to other off‐axis angles, we aim to investigate the effect of the off‐axis angle on the time‐dependent failure of UD glass/iPP, and to propose a lifetime prediction method for the off‐axis failure. Glass/iPP specimens with different off‐axis angles are tested at various strain rates, creep, and fatigue loads to characterize the anisotropic, time‐dependent mechanical response. It is demonstrated that the influences of strain rate and fiber orientation angle on tensile strength are multiplicatively separable; also referred to as factorizable, enabling one to characterize the angle dependence at a single strain rate and the strain rate dependence at a single angle. Moreover, similar to transverse loading, off‐axis failure is also observed to be plasticity‐controlled. Based on these observations, the lifetime prediction method for the plasticity‐controlled transverse failure is extended to off‐axis loading using the aforementioned factorazibility, which resulted in lifetime predictions in agreement with the experimental creep and fatigue data.

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

Cited by 55 publications

References 56 publications

Residual lifetime assessment of uPVC gas pipes

Residual lifetime assessment of uPVC gas pipes

Influence of fiber orientation, temperature and relative humidity on the long‐term performance of short glass fiber reinforced polyamide 6

Time‐dependent failure of off‐axis loaded unidirectional glass/iPP composites

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