The mechanism and a slip model for the initial plastic deformation of amorphous polyethylene under uniaxial tension

Fanlin Zeng, Enlai Hu, Yi Sun, Jianmin Qu

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Abstract

ABSTRACT The mechanical behaviors of a polyethylene (PE) bulk consisting of amorphous molecular chains under uniaxial tension have been explored using molecular simulations. The stress-strain relationship and the plastic deformations of the PE bulk have been analyzed. Two deformation stages were found in the stress-strain curve, the elastic stage with a straight linear part of the curve and the plastic stage with a flat sawtooth-like part. The Young's modulus calculated from the elastic part is in good agreement with experimental results. Some key parameters such as the energy variations in different terms reveal that the interchain slip should be chiefly responsible for the initial plastic deformations of amorphous PE under uniaxial tension. In order to address how this slip influences the plastic deformations, the mechanical details of a single chain have been elucidated when it was pulled out from two PE clusters consisting of regular and amorphous chains, respectively. The interchain slip, found as the basic movement style, is responsible for the movement of the stretched chain. Both the critical slip force and the critical slip length have been found in these two cases. For the straight chain pulled out from the cluster with regular chains, the critical slip force is about 1.81 nN and the critical slip length is about 40 polymerization degrees. While for the chain in the amorphous cluster, the critical force is about 0.86 nN and the critical length is almost the same. Based on the simulation results, a meso slip model has been deduced to explain the behaviors of the amorphous PE bulk under uniaxial tension. With reference to the slip model of single crystals and polycrystals a constitutive relation was obtained by considering the Young's modulus, the equivalent slip stress and the average orientation parameters of each chain. The comparison of the results from the constitutive relation and the simulations proves that this model does well in predicting the mechanical behaviors of amorphous PE under uniaxial tension in general.

Original languageEnglish
Pages (from-to)986-998
Number of pages13
JournalJournal of Polymer Science, Part B: Polymer Physics
Volume53
Issue number14
DOIs
StatePublished - 15 Jul 2015

Keywords

  • constitutive relation
  • mechanism
  • molecular mechanics
  • molecular modeling
  • polyethylene (PE)

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