Mechanical joint is the weakest link of any fibre reinforced polymer composite structures. The holes for the joints are often created through conventional mechanical drilling due to the technological know-how. Yet, delamination damage at the entry and the exit side of the drilled holes are critical defects that severely influence mechanical competence of the product. However, the main challenge in controlling and reducing thrust force during drilling operation is variation of mechanical properties of composite material, particularly for flax fibre based products. The influence and relationship of critical thrust force and feed rate on delamination damage in drilling flax natural fibre composites was investigated. Initially, the critical thrust force for minimal delamination damage was determined based on existing models for synthetic fibre reinforced polymer composites. A semi-empirical model that correlates feed rate with critical thrust force was established via regression analyses. This model allows prediction of critical feed rate at a constant cutting speed. The model could minimise the on-set delamination damage of the composite laminates. Experimental results confirmed that the delamination factor was mainly governed by the choice of feed rate. The inter-laminar strength of the flax fibre composite was attributed to the initiation of delamination damage. The critical strain release energy is significantly different in comparison with carbon and glass fibre composites counterparts.
