Static and fatigue failure mechanisms of a bio-sourced epoxy resin : towards a bio-based composite

Composites made of epoxy matrices are widely used in many sectors such as the automotive and aerospace sectors, but also in the development of sport equipment. However, most of the epoxies currently used for everyday life applications are petroleum-based. Growing environmental concerns are the driving force for the development of materials with a lower carbon-footprint such as biosourced composites made of a bio-sourced matrix and natural fibres. Before designing a composite, the properties and failure mechanisms of its constituents must be determined and understood. This work focuses on the mechanical characterization of the partially bio-sourced epoxy resin InfuGreen 810. This resin has been cured according to 2 different curing cycles in order to study their influence on the properties. For the first cycle, curing took place at 45°C while for the other one, it took place at room temperature. In both cases, the resin was then post-cured at 80°C. First, a constitutive model has been implemented based on data obtained under tensile and compression loading conditions for each curing cycle. This allowed to do some finite element analyses (FEA). Then, the fracture toughness has been determined by performing three point bending tests on SENB specimens and specimens with a chevron in their midden. Fracture toughness has also been determined via Digital Image Correlation (DIC) analyses. When InfuGreen 810 is cured at 45°C, it is about 2.43 MPa·m^0.5 while when the curing step occurs at room temperature, it is about 2.81 MPa·m^0.5. However, due to some difficulties to insert true pre-cracks in the specimens, fracture toughness can be overestimated and a lower value can be given in both cases. The lowest value are about 1.85 MPa·m^0.5 and 2.11 MPa·m^0.5 when InfuGreen 810 is cured at 45°C and at room temperature, respectively. Aside of this experimental campaign, finite element simulations have also been done to confirm the results. Finally, tension-tension fatigue tests have been performed. It has been determined that the studied epoxy resin has an endurance limit of about 35.6 MPa if the testing frequency is set to 10 Hz and the stress ratio to 0.1.