Back Stress in Modeling the Response of PEEK and PC
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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.
KeywordsMechanical 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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