Cyclic viscoplasticity of semicrystalline polymers with finite deformations

Observations are reported on low density polyethylene (LDPE) in uniaxial tensile cyclic tests (oscillations between maximum elongation ratios k(max)(n) and the zero minimum stress sigma(min) = 0 when k(max)(n) increases monotonically with number of cycles n). Experimental data demonstrate fading memory of deformation history: when specimens are subjected to two loading programs that differ along the first n - 1 cycles of deformation and coincide afterwards, their stress-strain diagrams become identical starting from the nth cycle. A constitutive model is developed in cyclic viscoplasticity of semicrystalline polymers with finite deformations, and its adjustable parameters are found by fitting the observations. Ability of the stress-strain relations to describe the fading memory phenomenon and to predict the mechanical response of LDPE in cyclic tests with various deformation programs is confirmed by numerical simulation. (C) 2012 Elsevier Ltd. All rights reserved.