Influence of the fibre–matrix interface on the behaviour of polypropylene reinforced by short glass fibres above glass transition temperature

This paper describes an experimental and theoretic study of the influence of the fibre–matrix interface on the behaviour of the polypropylene reinforced with 40% in mass of short glass fibres. Tensile tests show that three zones of behaviour, which are linear, non-linear without damage and non-linear with damage, exist for each material tested. Creep-recovery tests without damage were carried out on the polypropylene reinforced with treated and untreated short glass fibres. Five stress levels were used for the creep tests according to the three zones determined with the tensile tests. The creep-recovery tests show the presence of elasticity, viscoelasticity (linear and non-linear) and viscoplasticity. The elasticity and viscoelasticity are described by Schapery's nonlinear constitutive equation and the viscoplasticity by Zapas–Crissman's equation. The results show that the elastic, viscoelastic and viscoplastic strains are more significant for the materials with untreated fibres.