Modeling of multicycle deformation of polymers with various deformation programs

The purpose of this paper is to compare mechanical response of polypropylene in multicycle tensile tests with straincontrolled and mixed deformation programs and to develop constitutive equations that describe quantitatively the experimental data. Multicycle tensile tests are performed on isotactic polypropylene with straincontrolled (oscillations between fixed maximum and minimum strains) and mixed (oscillations between a fixed maximum strain and the zero minimum stress) programs. A constitutive model is derived in cyclic viscoelasticity and viscoplasticity of semicrystalline polymers, and its parameters are found by fitting observations. The effect of damage accumulation of material parameters is analyzed numerically. The model predicts accurately mechanical behavior of polypropylene in tests with numbers of cycles strongly exceeding those used to determine its parameters. In the regime of developed damage, material constants in the stressstrain relations are independent of deformation program. A novel constitutive model is derived in cyclic viscoelastoplasticity of semicrystalline polymers and comparison of its adjustable parameters is performed for different deformation programs.