Advanced mechanical properties of polymer foams and composites

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Due to the steady increase use of polymer foams and natural fibre composites in many day to day applications (building, transport, packaging, biomaterials), it becomes highly important to predict their long term properties and their limit of application (high deformation behavior up to break-up and fatigue). Several studies have been published, both experimental and theoretical, on modeling the properties at small deformation (mainly the elastic modulus). Unfortunately, very few data are available on higher deformation properties like strength and deformation at break. Furthermore, almost nothing is available on fatigue properties, especially as a function of temperature. It is proposed to study the complete stress-strain curve and fatigue of polymer foams and composites. To do so, three secondary objectives will be investigated: 1) to develop correlations for the complete stress-strain curve under different types of loadings (tension, compression, flexion and torsion); 2) to predict the lifetime of a part under different types of fatigue deformation; and 3) study the effect of temperature and on 1) and 2). As a continuation of our previous work and the growing interest of recyclability, a focus will be made on thermoplastic resins, mainly polyethylene (PE) and polypropylene (PP) for foaming. For composites, the same matrices will be used with natural fibres (wood, flax, hemp). The experimental data produced will increase our knowledge by reporting new data over a wider range of conditions than available in the literature. These data are of great importance, especially for people doing numerical simulations for code validation. The correlations developed will be very useful to engineers to predict the mechanical behavior under different conditions (temperature and rates) and type of loading (compression, tension, flexion, torsion and fatigue). They will help to design structural applications where safety factors must be carefully known.