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Time-Dependent Mechanical Behavior of Polymers and Polymer Composites, 2nd Edition

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Physics and Theory".

Deadline for manuscript submissions: closed (10 October 2024) | Viewed by 2313

Special Issue Editor


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Guest Editor
College of Civil Engineering and Mechanics, Xiangtan University, Xiangtan 411105, China
Interests: viscoelasticity; time-temperature-stress superposition; hyperlasticity; time-dependent fracture; nonlinear creep; fractional derivative constitutive model; dynamical mechanical analysis; fatigue life; damage; thermomechanical coupling
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Special Issue Information

Dear Colleagues,

The wide application of polymers and polymer composites in various engineering fields demonstrates the need to accurately describe the mechanical behavior and mechanical properties of these materials under complex loading conditions. The characteristics of polymer mechanical behavior are mainly related to rheology, that is, the dependence of time, temperature, load frequency and rate, etc., showing viscoelasticity, viscohyperelasticity, viscoelastoplasticity, and so on. This Special Issue aims to present recent advances in the testing and modeling of the mechanical response of polymers and their composites under complex loads, including, but not limited to, the following topics:

  • Long-term mechanical properties;
  • Creep and relaxation behavior;
  • Dynamic mechanical analysis;
  • Constitutive modeling;
  • Rate-dependent mechanical behavior;
  • Time-dependent failure;
  • Physical aging;
  • Damage and fracture;
  • Fatigue behavior;
  • Multiaxial testing;
  • Multiscale modeling;
  • Thermorheological behavior.

Prof. Dr. Wenbo Luo
Guest Editor

Manuscript Submission Information

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Keywords

  • mechanical properties
  • constitutive model
  • viscoelasticity
  • viscohyperelasticity
  • viscoplasticity
  • mechanical testing
  • damage
  • fracture
  • fatigue
  • physical aging

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Related Special Issue

Published Papers (2 papers)

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Research

12 pages, 3052 KiB  
Article
A Description of the Isothermal Ageing Creep Process in Polymethyl Methacrylate Using Fractional Differential Models
by Chuhong Wang and Xin Chen
Polymers 2024, 16(19), 2725; https://doi.org/10.3390/polym16192725 - 26 Sep 2024
Cited by 2 | Viewed by 799
Abstract
Fractional differential viscoelastic models can describe complex material behaviours and fit experimental data well; however, the physical significance of model parameters is difficult to express. In this study, the fractional differential Maxwell, Kelvin, and Zener models were used to fit the short-term creep [...] Read more.
Fractional differential viscoelastic models can describe complex material behaviours and fit experimental data well; however, the physical significance of model parameters is difficult to express. In this study, the fractional differential Maxwell, Kelvin, and Zener models were used to fit the short-term creep compliance curves of polymethyl methacrylate at different ageing times. The model fits were in good agreement with the experimental data. As the ageing time increased, the fractional differential Zener model showed a relative increase in the modulus parameter of the spring and a relative decrease in the modulus parameter reflecting the viscosity of the spring-pot, which indicated that physical ageing made the material more elastic. The relaxation time of the material increased, which indicated that the physical ageing reduced the free volume of the material, hindered the movement of molecules/segments, and increased the time required for the material to reach equilibrium. The fractional order of the model decreased, which reflected the phenomenon that physical ageing reduced the creep compliance of the material. Using the relaxation time as the time scale, the creep curves at different ageing times under the same stress level could be superimposed, naturally presenting the time–ageing time equivalence principle. Full article
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33 pages, 10955 KiB  
Article
Robust Recovery of Optimally Smoothed Polymer Relaxation Spectrum from Stress Relaxation Test Measurements
by Anna Stankiewicz
Polymers 2024, 16(16), 2300; https://doi.org/10.3390/polym16162300 - 14 Aug 2024
Cited by 2 | Viewed by 1020
Abstract
The relaxation spectrum is a fundamental viscoelastic characteristic from which other material functions used to describe the rheological properties of polymers can be determined. The spectrum is recovered from relaxation stress or oscillatory shear data. Since the problem of the relaxation spectrum identification [...] Read more.
The relaxation spectrum is a fundamental viscoelastic characteristic from which other material functions used to describe the rheological properties of polymers can be determined. The spectrum is recovered from relaxation stress or oscillatory shear data. Since the problem of the relaxation spectrum identification is ill-posed, in the known methods, different mechanisms are built-in to obtain a smooth enough and noise-robust relaxation spectrum model. The regularization of the original problem and/or limit of the set of admissible solutions are the most commonly used remedies. Here, the problem of determining an optimally smoothed continuous relaxation time spectrum is directly stated and solved for the first time, assuming that discrete-time noise-corrupted measurements of a relaxation modulus obtained in the stress relaxation experiment are available for identification. The relaxation time spectrum model that reproduces the relaxation modulus measurements and is the best smoothed in the class of continuous square-integrable functions is sought. Based on the Hilbert projection theorem, the best-smoothed relaxation spectrum model is found to be described by a finite sum of specific exponential–hyperbolic basis functions. For noise-corrupted measurements, a quadratic with respect to the Lagrange multipliers term is introduced into the Lagrangian functional of the model’s best smoothing problem. As a result, a small model error of the relaxation modulus model is obtained, which increases the model’s robustness. The necessary and sufficient optimality conditions are derived whose unique solution yields a direct analytical formula of the best-smoothed relaxation spectrum model. The related model of the relaxation modulus is given. A computational identification algorithm using the singular value decomposition is presented, which can be easily implemented in any computing environment. The approximation error, model smoothness, noise robustness, and identifiability of the polymer real spectrum are studied analytically. It is demonstrated by numerical studies that the algorithm proposed can be successfully applied for the identification of one- and two-mode Gaussian-like relaxation spectra. The applicability of this approach to determining the Baumgaertel, Schausberger, and Winter spectrum is also examined, and it is shown that it is well approximated for higher frequencies and, in particular, in the neighborhood of the local maximum. However, the comparison of the asymptotic properties of the best-smoothed spectrum model and the BSW model a priori excludes a good approximation of the spectrum in the close neighborhood of zero-relaxation time. Full article
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