Stress- and strain-controlled cyclic deformation of polypropylene

Experimental data are reported on isotactic polypropylene in uniaxial tensile cyclic tests with stress- and strain-controlled programs. A constitutive model is developed that adequately describes stress–strain diagrams, and its parameters are found by fitting the observations. Numerical simulation demonstrates that fatigue failure in ratcheting tests is induced by pronounced growth of plastic strain in crystallites.