A. Cohades, N. Hostettler, V. Michaud
EPFL-LPAC,
Switzerland
Keywords: composites, self-healing, impact damage, durability, fatigue
Summary:
Fibre-Reinforced Polymer (FRP) composite structures processed by Liquid Composite Moulding (LCM) are widely used in aerospace, automotive, windmills and sports industries; a design limitation with these materials is however their matrix brittleness and sensitivity to small damage events. We developed a novel matrix concept for a structural FRP that (i) is tougher than commercial benchmark epoxy-based composites, (ii) can heal matrix microcracks and (iii) has a manufacturing route compatible with LCM. A precisely tuned matrix microstructure forms during processing, and consists of an interpenetrating network of interconnected thermoset particles and thermoplastic matrix, providing added intrinsic toughness. Upon heating, the thermoplastic phase flows and heals microcracks. This strategy was successfully demonstrated for the first time using glass reinforcements. Impact damage events up to 20 Joules energy were healed after heating the structure to 150°C, while strength and stiffness were overall maintained, and initial toughness increased. We then extended the characterisation of such composites to other industrially based properties: fatigue and durability assessment. We observed a considerable life-time extension for healable composites compared to benchmark composites; fatigue life of healable composites demonstrated a life-time extension of at least 3 times. With durability experiments, a negligible reduction in strength after temperature and humidity cycles was shown as compared to benchmark systems. Overall, we demonstrated that our new healing matrices for composites are competitive in terms of multiple repair ability, fatigue and durability while preserving similar mechanical properties and processing method as in many industrial systems.