Back Stress in Modeling the Response of PEEK and PC

  • Wenlong Li
  • George Gazonas
  • Eric N. Brown
  • Philip J. Rae
  • Mehrdad NegahbanEmail author
Conference paper
Part of the Conference Proceedings of the Society for Experimental Mechanics Series book series (CPSEMS)


With the development of new methods for the characterization of equilibrium stress through cyclic loading, it is now possible to follow the evolution of back stress during the nonlinear deformation of polymers. Experiments on PEEK and PC below the glass-transition temperature indicate a back stress that may evolve with plastic deformation, and which is substantially different from that seen during the response in the rubbery range. In particular, the back stress during the response of PC shows the characteristic post-yield softening, possibly indicating that the observed post-yield softening in the response comes from the back stress. This is not seen in PEEK, which also shows no substantial post-yield softening. The equilibrium stress plays a central role in modeling both the quasi-static and dynamic response of PEEK.


Mechanical modeling Plastic flow Equilibrium stress Thermal expansion Digital image correlation 



The research was partially supported by the US Army Research Laboratory through Contract Number W911NF-11-D-0001-0094. The experiments were completed by utilizing the stress analysis facility at the University of Nebraska-Lincoln.


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Copyright information

© The Society for Experimental Mechanics, Inc. 2017

Authors and Affiliations

  • Wenlong Li
    • 1
  • George Gazonas
    • 2
  • Eric N. Brown
    • 3
  • Philip J. Rae
    • 3
  • Mehrdad Negahban
    • 1
    Email author
  1. 1.Mechanical and Materials EngineeringUniversity of Nebraska-LincolnLincolnUSA
  2. 2.U.S. Army Research LaboratoryAberdeen Proving GroundAberdeenUSA
  3. 3.Los Alamos National LaboratoryLos AlamosUSA

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