A constitutive model for block-copolymers based on effective temperature. (October 2019)

• Record Type: Journal Article
• Authors: Das, Sanhita; Roy, Debasish
• Is Part Of: International journal of mechanical sciences. Volume 161/162(2019)
• Publication Date: 2019-10
• Subjects: Effective-temperature -- Polymer -- Glass transition -- Viscoelasticity -- Structural relaxation -- Effective temperature -- Physical ageing -- Mechanical rejuvenation -- Polyurea -- Copolymer -- Slow indentation -- Thermoplastic elastomers; Mechanical engineering -- Periodicals; Génie mécanique -- Périodiques; Mechanical engineering; Maschinenbau; Mechanik; Zeitschrift; Periodicals; 621.05
• DOI: 10.1016/j.ijmecsci.2019.105082
• Languages: English
• ISSNs: 0020-7403

Abstract

Highlights: A micro-mechanical model for elastomeric copolymers generalised to block-copolymers. Use of effective temperatures enables temperature/strain driven phase-transition. Captures monotonic and cyclic uniaxial response for various strain rates. Captures mechanical response under a general state of stress. Incorporates volume fraction and glass transition temperature of each domain. Graphical abstract: Abstract: Phase segregated copolymers such as elastomeric copolymers find myriad applications especially in impact resistant structures. When domains with varying relaxation characteristics are present, these polymers exhibit thermorheologically complex behaviour. The multiple relaxation processes are herein captured using the effective temperature based thermodynamics, used extensively in modelling thermo-mechanical response of metals and polymers. Specifically, we use two slowly evolving configurational subsystems and a fast evolving kinetic-vibration (K-V) subsystem. The two configurational subsystems represent the inter-molecular and intra-molecular meso-scale configurational transformations occurring within the two domains. The K-V subsystem represents the faster atomic vibrations. The configurational subsystems are weakly coupled with the K-V through heat exchange which accounts for structural relaxations of the individual domains towards the equilibrium microstructure. Based on this, we are able to capture strain rate dependence and strain induced softening of these materials under cyclic loads. In comparison with the existing formulations for such copolymers, ours is perhaps a more transparent approach, as it uses quantities such as volume fraction, glass transition temperatures of individual domains as material parameters. Indeed, our formulation could be readily adapted for non-elastomeric copolymers. It should also be potentially useful as a design tool for copolymers with increased glass transition range.