Influence of temperature on viscoelastic–viscoplastic behavior of poly(lactic acid) under loading–unloading

Düşünceli, Necmi; Drozdov, Aleksey D.; Theilgaard, Naseem

doi:10.1002/pen.24404

Cited by 5 publications

(3 citation statements)

References 40 publications

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“…Guedes et al [41] report stress relaxation on a PLA-PCL (polycaprolactone) blend at room temperature and at strains up to 0.16, and were able to model the results using linear viscoelasticity. Duscunceli et al [42] have studied stress relaxation of PLA at small strains and up to 50 °C. For conditions closer to those of this study, Sweeney et al [43] report stress relaxation for a PLA-CaCO 3 composite at a strain of 3.0 in the temperature range 60–70 °C, with initial loading at an average strain rate of 0.036 s −1 .…”

Section: Resultsmentioning

confidence: 99%

Modelling the Mechanical and Strain Recovery Behaviour of Partially Crystalline PLA

Sweeney¹,

Spencer²,

Nair³

et al. 2019

Polymers

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This is a study of the modelling and prediction of strain recovery in a polylactide. Strain recovery near the glass transition temperature is the underlying mechanism for the shape memory in an amorphous polymer. The investigation is aimed at modelling such shape memory behaviour. A PLA-based copolymer is subjected to stress–strain, stress relaxation and strain recovery experiments at large strain at 60 °C just below its glass transition temperature. The material is 13% crystalline. Using published data on the mechanical properties of the crystals, finite element modelling was used to determine the effect of the crystal phase on the overall mechanical behaviour of the material, which was found to be significant. The finite element models were also used to relate the stress–strain results to the yield stress of the amorphous phase. This yield stress was found to possess strain rate dependence consistent with an Eyring process. Stress relaxation experiments were also interpreted in terms of the Eyring process, and a two-process Eyring-based model was defined that was capable of modelling strain recovery behaviour. This was essentially a model of the amorphous phase. It was shown to be capable of useful predictions of strain recovery.

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Section: Resultsmentioning

confidence: 99%

Modelling the Mechanical and Strain Recovery Behaviour of Partially Crystalline PLA

Sweeney¹,

Spencer²,

Nair³

et al. 2019

Polymers

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“…During loading and unloading, rates of plastic flow and relaxation develop exponentially with temperature. 67…”

Section: Discussionmentioning

confidence: 99%

“…We previously conducted extensive breakage, cyclic, and relaxation tests on PLA, whose some parts were presented in this study. 50,67 Results of uniaxial tensile breakage tests at 50, 5 and 1 mm/min revealed dependency of strain rate on deformation behavior of PLA. For repeatability and precision of measured strains, the cross head speed d· = 1 mm/min was selected.…”

Section: Experimental Testsmentioning

confidence: 96%

An observation of the evolution of equilibrium stress on poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites

Düşünceli

2020

Proceedings of the Institution of Mechanical Engineers, Part C:

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Relaxation behavior provides specific information that indicates stress development with elapsed time for the determination of material characterization and constituting of material modeling. In addition, anomalous relaxation behavior of polymeric materials enables experimental analysis of some theoretical variables in constitutive equation. Equilibrium stress is one of the most prevailing variables in material modeling and it is generally considered as unmeasurable. In this study, evolution of equilibrium stress was examined with relaxation tests of two semi crystalline polymer materials, one of which was found to reach precise equilibrium stress levels. In accordance with this purpose, extensive relaxation tests were conducted on poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites specimens at a wide range of temperatures from 23 ℃ and 55 ℃, and stress levels from 1 MPa to 50 MPa for poly(lactic acid) and 51 MPa for poly(lactic acid)/hydroxyapatite nanocomposites. All the specimens were subjected tensile loading–unloading and partial retraction process. The starting points of the relaxation test were chosen on unloading segment of stress–strain curves. Evolution of stress may decay, increase or decay then increase depending on the test point on unloading curves. Relaxation behavior of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites was simulated using viscoplasticity theory based on overstress for polymeric materials. Experimental results of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites were matched with numerical results of viscoplasticity theory based on overstress for polymeric materials, and viscoplasticity theory based on overstress for polymeric material model was found to have an aptitude for predicting anomalous relaxation behavior of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites. Additionally, the effect of temperature on relaxation time was investigated with using Kohlraush–Williams–Watts time-decay function. Modeling capability of Kohlrausch–Williams–Watts model was reasonable to predict short-term simple relaxation of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites. Responses of the model showed that interaction between relaxation time and environmental temperature was related to transition from glass state to rubbery state.

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Characterization of loading, relaxation, and recovery behaviors of high‐density polyethylene using a three‐branch spring‐dashpot model

Shi,

Jar

2024

Polymer Engineering & Sci

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This paper presents an analysis of the stress evolution of high‐density polyethylene (HDPE) at loading, relaxation, and recovery stages in a multi‐relaxation‐recovery (RR) test. The analysis is based on a three‐branch spring‐dashpot model that uses the Eyring's law to govern the viscous behavior. The spring‐dashpot model comprises two viscous branches to represent the short‐ and long‐term time‐dependent stress responses to deformation, and a quasi‐static branch to represent the time‐independent stress response. A fast numerical analysis framework based on genetic algorithms was developed to determine values for the model parameters so that the difference between the simulation and the experimental data could be less than 0.08 MPa. Using this approach, values of the model parameters were determined as functions of deformation and time so that the model can simulate the stress response at loading, relaxation, and recovery stages of the RR test. The simulation also generated 10 sets of model parameter values to examine their consistency. The study concludes that the three‐branch model can serve as a suitable tool for analyzing the mechanical properties of HDPE, and values for the model parameters can potentially be used to characterize the difference among PEs for their mechanical performance.Highlights Developed computer programs to determine parameter values automatically. Explained the unusual stress drop during stress recovery after unloading. Evaluated the statistical range of the parameter values for the good fitting.

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Influence of temperature on viscoelastic–viscoplastic behavior of poly(lactic acid) under loading–unloading

Cited by 5 publications

References 40 publications

Modelling the Mechanical and Strain Recovery Behaviour of Partially Crystalline PLA

Modelling the Mechanical and Strain Recovery Behaviour of Partially Crystalline PLA

An observation of the evolution of equilibrium stress on poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites

Characterization of loading, relaxation, and recovery behaviors of high‐density polyethylene using a three‐branch spring‐dashpot model

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