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Modelling of loading, stress relaxation and stress recovery in a shape memory polymer
Sweeney, John Bonner, M. Ward, Ian M.
Sweeney, John
Bonner, M.
Ward, Ian M.
Publication Date
2014-09
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© 2014 Elsevier. Reproduced in accordance with the publisher's selfarchiving
policy. This manuscript version is made available under the CC-BY-NC-ND 4.0
license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Peer-Reviewed
Yes
Open Access status
openAccess
Accepted for publication
2014-05-03
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Abstract
A multi-element constitutive model for a lactide-based shape memory polymer has been developed that represents loading to large tensile deformations, stress relaxation and stress recovery at 60, 65 and 70°C. The model consists of parallel Maxwell arms each comprising neo-Hookean and Eyring elements. Guiu-Pratt analysis of the stress relaxation curves yields Eyring parameters. When these parameters are used to define the Eyring process in a single Maxwell arm, the resulting model yields at too low a stress, but gives good predictions for longer times. Stress dip tests show a very stiff response on unloading by a small strain decrement. This would create an unrealistically high stress on loading to large strain if it were modelled by an elastic element. Instead it is modelled by an Eyring process operating via a flow rule that introduces strain hardening after yield. When this process is incorporated into a second parallel Maxwell arm, there results a model that fully represents both stress relaxation and stress dip tests at 60°C. At higher temperatures a third arm is required for valid predictions.
Version
Accepted manuscript
Citation
Sweeney J, Bonner M and Ward IM (2014) Modelling of loading, stress relaxation and stress recovery in a shape memory polymer. Journal of Mechanical Behavior of Biomedical Materials. 37: 12-23.
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Article