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The Breaking Process of an Idealized Polymeric Bundle under Applied Tensile Stress
Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, Department of Physics.
2014 (English)MasteroppgaveStudent thesis
Abstract [en]

We introduce a particle-based model of an idealized polymeric bundle, whose properties are investigated by means of molecular dynamics simulations. We analyse in particular the effect of applying a tensile stress, stretching and eventually breaking the bundle. The simulation results show that, despite its simplicity, the model captures characteristic features of polymeric materials, e.g. a multistage creep and creep ringing. The results indicate that the system evolves in a near-equilibrium state during almost the entire creep process, reflected in the data collapse of the \emph{effective stress--strain} curve. Two distinct variants of the basic model are studied, the first one allowing and the second one disallowing recombination of broken bonds. The former model is observed to undergo a phase transition, taking place at a critical tensile force $F_c$. Below this threshold, the bundle is observed to stabilize, and above the threshold, the bundle breaks down. In both model assumptions, the bundle lifetime $t_f$ seems to exhibit Basquin-like power-law dependence upon the applied force $F$; for the former this is estimated to be $t_f \sim F^{-\gamma}$, with $\gamma = 4 \pm 0.1$. Simulation results follow the same power law over the accessible range in $F$, spanning about half a decade. The elongation difference as a function of normalized time also shows a remarkable data collapse for a range in $F$, hinting to universality in the creep process. Moreover, at imminent failure, the strain rate is shown to grow as $\dot{L} \sim \tau_{\rm ttf}^{-1}$, where $\tau_{\rm ttf}$ is the normalized time-to-failure. This is in excellent agreement with recent experimental findings for a protein gel \cite{leocmach2014creep}. New theoretical approaches are also made to understand the breaking process of a bundle of polymers. In particular, a simple one-step fiber bundle model is proposed. The model may serve to explain the phase transition that was observed for the simulation model that allowed for recombination.

Place, publisher, year, edition, pages
Institutt for fysikk , 2014. , 114 p.
URN: urn:nbn:no:ntnu:diva-26873Local ID: ntnudaim:10972OAI: diva2:752478
Available from: 2014-10-03 Created: 2014-10-03 Last updated: 2014-10-03Bibliographically approved

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