On the notch sensitivity of flax fibre metal laminates under static and fatigue loading

Damage progression and failure characteristics of open-hole flax fibre aluminium laminate (flax-FML) specimens subjected to quasi-static tensile or tension-tension fatigue loading were experimentally investigated. Notched and unnotched flax-FML composites exhibited brittle fracture with little or no fibre pull-out and minimal delamination at the aluminium/adhesive interface. The flax-FMLs were tested to failure under tension-tension fatigue loading conditions (R ratio of 0.1; frequency of 10Hz; applied fatigue stresses ranging between 30% and 80% of the respective ultimate tensile strength values). The fatigue cycles to failure decreased with the increase in the applied fatigue stress and hole diameter. A phenomenological modelling technique was developed to evaluate the fatigue life of an open-hole flax-FML composite. Fatigue tests on specimens subjected to a maximum load equivalent to 35% of the respective tensile failure strength were interrupted at around 85% of the corresponding fatigue life. The accumulated fatigue damage in these specimens was characterised using X-ray computed tomography. For benchmarking purposes, the fatigue performance and related damage progression in the flax-FML composite were compared with those of the glass-FMLs.