A multiprocess eyring model for large strain plastic deformation

Abstract

A multiprocess Eyring model is developed with a particular aim of predicting the localized instability occurring in ''necking'' polymers when cold-drawn. Differences from using single and multiple Eyring processes are examined using a published data-set for polypropylene test pieces; it is shown that a four Eyring process model can simultaneously fit both necking stretch ratio and draw force data for uniaxial stretching, whereas with a single process only one measurement could be fitted accurately. The multi process Eyring model is shown to give significantly more accurate predictions than a necking hyperelastic model. The multiprocess model is assessed against the same material undergoing a complex constant-width elongation. It is shown that agreement is quantitatively good for both drawing force and surface deformation, with some minor differences in transverse force and surface stretch. A pronounced intermittent stretching pattern that is seen on the experimental test piece is replicated by the multiprocess Eyring simulation, but is absent using the hyperelastic model. A method is described to deform a photograph of the original specimen according to a finite element solution. The method is shown to give a clear indication of the accuracy of the model in predicting final form.

Characterization of Polyethylene Using a New Test Method Based on Stress Response to Relaxation and Recovery

“…The three spring-dashpot models considered for the data analysis are depicted in Figure 3 , namely, the standard model [ 17 ], the Parallel model [ 33 , 34 , 35 , 36 ], and the Series model [ 37 ]. For each model, the lower branch in Figure 3 represents the response to deformation and the upper branch the viscous counterpart.…”

“…Three spring-dashpot models, including the standard model [ 6 ], the Parallel model, also considered in Refs. [ 33 , 34 , 35 , 36 ], and the Series model, were applied to simulate the relaxation and recovery behavior in the RR test, to extract the model parameters by fitting the experimentally determined engineering stress-displacement curves. Each of these models consists of two branches, one being a viscous branch to simulate the time-dependent stress response to deformation, and the other a quasi-static branch to simulate the time-independent stress response.…”