Characterisation and micromechanical modelling of the elasto-viscoplastic behavior of thermoplastic elastomers

The first objective of this study is to characterise the physico-chemical and mechanical properties of thermoplastic elastomers (TPE) and their constituents. In parallel with the experimental study, a model describing the mechanical behaviour of such materials at room temperature and without damage is proposed. The composite materials studied in the present work are processed by blending particles of vulcanized rubber ethylene-propylene-diene (EPDM) into an isotactic polypropylene (PP) matrix. These particles, obtained from a recycling process, have an average diameter of 70 μm. The constitutive equation for TPE composites is developed within the framework of a self-consistent micromechanical approach which considers the mechanical behaviour of each phase. A preliminary analysis of various TPE in linear elasticity justifies the choice of a morphological pattern for the model, which views elastomer particles as embedded in the thermoplastic matrix. In the non-linear domain, the PP matrix is modelled by means of an elastoviscoplastic model whose parameters are fitted using tensile and instrumented spherical micro-indentation tests. The elastomer exhibits viscoelastic behaviour. Having determined the material parameters by inverse analysis, the proposed micromechanical model is compared with tensile and bending tests performed before damage initiation and for various elastomers contents.