Micromechanical Modeling of the Elasto‐Viscoplastic Stress–Strain Response of <i>α</i>‐<scp>iPP</scp>

ABSTRACT The mechanical properties of semi‐crystalline polymers are dictated by the individual characteristics of crystalline and amorphous phases and the complex interplay between them. Processing conditions can strongly influence micro‐structural features such as crystallinity and orientation of crystalline structures, thereby changing the polymer behavior. In the present study, we employ a micromechanical composite inclusion model to obtain a direct relation between the microstructure and the resulting properties for alpha isotactic polypropylene (α‐iPP). The model uses a dedicated constitutive law for each constituent phase, thus capturing the elasto‐viscoplastic phenomena of both the isotropic amorphous and anisotropic crystalline phases. As such, it is intrinsically capable of covering the macro‐mechanical effects of texture evolution caused by crystalline slip. The model parameters for crystalline and amorphous phases of isotropic α ‐iPP are identified by comparing the model output with experimental results of uniaxial compression and tension tests at different strain rates and temperatures. Finally, the long‐term response of α ‐iPP in uniaxial creep loading is predicted and compared to experimental results.