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 ^kmax(n) and the zero minimum stress ^σmin=0 when ^kmax(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.