Ricardo Simoes (a,b), Anonio M Cunha (a) and Witold Brostow (c, d)

(a) Institute for Polymers and composites, Department of Polymer Engineering, University of Minho, 4800-058 Guimaraes, Portugal; rsimoes@ipca.pt, amcuhna@dep.uminho.pt
(b) School of Technology, Plytechnic Institute of Cavado and Ave, 4750-117 Barcelos, Portugal
(c) Laboratory of Advanced Polymers and Optimized Materials (LAPOM), Department of Materials Science, University of North Texas, Denton, TX 76203-5310, USA; Denton, TX 76203, USA; brostow@unt.edu
(d) College of Mechanics and robotics, University of Science and Technology, Adama Michiewicza 30, 30-059 Cracow, Poland.

ABSTRACT

Molecular dynamics simulations were employed to study the mechanical properties and true stress development in amorphous polymeric materials. As expected, the true stress levels are much higher than those indicated by the engineering stress. However, the true stress behaviour was found to be not only quantitatively but also qualitatively different from that of the engineering stress. Highly localized deformation results in abrupt increases of the true stress in certain regions, favoring crack formation and propagation. The computer-generated materials exhibit viscoelastic recovery curves similar to those seen in experiments. The recovery process is non-homogeneous and affected by the spatial arrangement of the amorphous chains. The loading conditions determine the preferential deformation mechanisms and influence the extent of recovery. Some deformation mechanisms are not recovered and contribute to permanent deformation.