NANOLIFE

High performance thermoplastic composites are a promising option to lighten vehicles in the scope of sustainable development. Focusing specifically on thermoplastic nanocomposites, their fatigue resistance is critical for most applications. Some works report improved fatigue resistance after loading epoxy with nanoparticles, whereas no work exists on the role of particle size and interphase properties on the fatigue life of thermoplastic nanocomposites. The NANOLIFE project aims to understand the molecular mechanisms governing the formation and propagation of cracks in the vicinity of nanoparticles in correlation with their effect on macroscopic fatigue properties. Our holistic approach covers from the particle chemistry to the fatigue characterization and lifespan prediction. As the mechanical response of nanocomposites is highly system-dependent, we chose as a model system silica spheres dispersed in an amorphous glassy matrix. The particles will be grafted with well-defined polymer chains to explore the effects of cohesion between the matrix and the interphase. The interphase thickness and entanglement rate will be screened by i) changing the particle size, grafting density and chain length and ii) implementing dynamic crosslinks in the interphase to trap entangled matrix chains within a dynamic covalent network. The mechanical tests will enable to link the interphase properties to failure modes with a multiscale approach. Digital image correlation and infrared thermography monitoring during crack propagation fatigue tests will be applied to access local strains near the crack tip and crack propagation rate. Damage mechanisms will be identified from thermographic data recorded during tensile-tensile fatigue to predict lifespan. In parallel to the experimental work, numerical approaches will bring understanding in chain conformation, dynamics and interfacial adhesion with grafted nanoparticles as well as initiation of the damage during fatigue cycles.