A constitutive model for thermoplastics based on two temperatures

Das, Sanhita and Chowdhury, Shubhankar Roy and Roy, Debasish (2018) A constitutive model for thermoplastics based on two temperatures. In: EUROPEAN JOURNAL OF MECHANICS A-SOLIDS, 72 . pp. 440-451.

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Abstract

Posed within a two-temperature thermodynamic framework, our aim is to propose a unified glass-rubber constitutive model for thermo-rheologically simple thermoplastic polymers. This modelling set-up usually applies to phenomena wherein sub-macroscopic processes involving different time scales occur and accordingly the thermodynamic system may be interpreted as comprising of two subsystems. The configurational subsystem contains the slower states, while the kinetic-vibrational subsystem comprises of the faster moving states. The two subsystems fail to equilibrate within experimental timescales in the glassy regime (low temperature or high strain rate) due to low structural relaxation rates. As transition to the rubbery regime commences at temperatures higher than glass transition or at sufficiently low loading rates, the two subsystems equilibrate within microscopic timescales. The model exploits physically inspired prescriptions for the free energies due to different underlying mechanisms-elastic stretching, localised shear transformations and infra-molecular straightening of chains. A simple temperature dependent formulation for structural relaxation in terms of heat transfer between the subsystems is used to capture transition between these mechanisms. The model is then validated against experimental results of uniaxial compression tests for various strain rates and temperatures establishing its ability to seamlessly transit between the glassy and rubbery regimes. Also demonstrated is the model's efficacy in capturing the key features of physical ageing and mechanical rejuvenation.

Item Type:	Journal Article
Publication:	EUROPEAN JOURNAL OF MECHANICS A-SOLIDS
Publisher:	ELSEVIER SCIENCE BV
Additional Information:	Copy right for this article belong to ELSEVIER SCIENCE BV
Keywords:	Two temperature thermodynamics; Polymer; Strain softening; Secondary hardening; Glass transition; Viscoelasticity; Structural relaxation; Effective temperature; Physical ageing; Mechanical rejuvenation
Department/Centre:	Division of Mechanical Sciences > Civil Engineering
Date Deposited:	13 Nov 2018 15:25
Last Modified:	24 Nov 2018 15:22
URI:	http://eprints.iisc.ac.in/id/eprint/61033

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