Fading memory of loading history in polypropylene and a polypropylene/clay nanocomposite

Experimental data are reported for neat polypropylene and a polypropylene/clay nanocomposite in multistep uniaxial cyclic tensile tests at room temperature (oscillations between maximum strains and the zero minimum stress, with the maximum strains increasing monotonically with number of cycles). The fading memory of deformation history is observed: when two test specimens are subjected to loading programs that differ during the first n − 1 cycles and coincide afterwards, their stress–strain diagrams become identical starting from the nth cycle. Constitutive equations are developed in the cyclic viscoelasticity and viscoplasticity of nanocomposites with semicrystalline matrices, and the adjustable parameters of the stress–strain relations are determined by fitting them to experimental data. The ability of the model to predict the fading memory phenomenon is confirmed by numerical simulations.