In this study, a non-linear viscoelastic-viscoplastic constitutive equation for polyamide 6 (PA6) is formulated and a new model is suggested for the viscoplastic part of the equation. The suggested model is empirical but can accurately predict the viscoplastic strain. In this study, creep and recovery tests are conducted to evaluate the viscoplastic strain. Using a non-linear dashpot, a viscoplastic strain is formulated and its parameters are identified for PA6. In addition, a stress relaxation test is conducted, and the relationship between the viscoelastic strain and stress is identified when considering the viscoplastic strain. In this study, the time-temperature superposition principle is thoroughly applied to include the effect of elevated temperature on the viscoelastic-viscoplastic behavior. All material constants in the non-linear viscoelastic-viscoplastic constitutive equation including the time-temperature superposition principle for PA6 are presented in this study.
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http://dx.doi.org/10.1016/j.heliyon.2021.e06335 | DOI Listing |
J Mech Behav Biomed Mater
January 2025
Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, United Kingdom. Electronic address:
This study investigates the mechanical behaviour of poly(ɛ-caprolactone) (PCL) continuous filaments produced by a novel electrospinning (ES) method. These filaments can be processed into woven or braided structures, showing great promises as scaffolds for ligament and tendon repair. Mechanical characterisation of the filaments using DMA and uniaxial tensile tests shows that the filament response is viscoelastic-viscoplastic.
View Article and Find Full Text PDFSci Rep
November 2024
Guangxi Key Laboratory of Geomechanics and Geotechnical Engineering, Guilin University of Technology, Guilin, 541004, China.
On the basis of the law of conservation of energy, the three stages of rock creep are analyzed. The reasons for the difficulty in studying the accelerated creep stage of rocks using the traditional creep model are expounded. The triaxial creep deformation law and critical point parameter values of rocks are obtained by carrying out rock creep tests under different confining pressures.
View Article and Find Full Text PDFMaterials (Basel)
October 2024
Laboratory of Manufacturing Technology, School of Mechanical Engineering, National Technical University of Athens, Heroon Polytechniou 9, 15780 Athens, Greece.
This work studies numerically the development of adiabatic shear banding (ASB) during high strain-rate compression of AISI 1045 steel. Plane strain and cylindrical axisymmetric compressions are simulated in LS-DYNA, considering rectangular and cylindrical steel samples, respectively. Also, a parametric analysis in height-to-base ratio is conducted in order to evaluate the effect of geometry and dimensional ratio of the sample on ASB formation.
View Article and Find Full Text PDFInt J Pharm
November 2024
Univ. Bordeaux, CNRS, Bordeaux INP, I2M, UMR 5295, F-33400 Talence, France; Arts et Metiers Institute of Technology, CNRS, Bordeaux INP, Hesam Universite, I2M, UMR 5295, F-33400 Talence, France.
Relaxation tests are often used in the pharmaceutical field to assess the strain rate sensitivity of pharmaceutical powders and tablets. These tests involve applying a constant strain to the powder in the die and then monitoring the stress evolution over time. Interpreting these tests is complicated because different physical phenomena, mainly viscoelasticity and viscoplasticity, occur simultaneously.
View Article and Find Full Text PDFMaterials (Basel)
July 2024
NOMATEN Centre of Excellence, National Centre for Nuclear Research, Sołtana 7, 05-400 Otwock, Poland.
This paper describes an application of a machine learning approach for parameter optimization. The method is demonstrated for the elasto-viscoplastic model with both isotropic and kinematic hardening. It is shown that the proposed method based on long short-term memory networks allowed a reasonable agreement of stress-strain curves to be obtained for cyclic deformation in a low-cycle fatigue regime.
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