Critical thrust force and critical feed rate in drilling flax fibre composites: A comparative study of various thrust force models

Past experimental and analytical studies for determination of critical thrust force that contributed toward minimal delamination damage in drilling synthetic fibre reinforced composites have failed to consider the recently developed natural fibre composites. From this point of view, critical thrust force and feed rate in drilling of flax fibre composites were comprehensively investigated. Three different thrust force models that were based on linear elastic fracture mechanics and properties of the composites; namely, Mode I interlaminar fracture toughness, Young modulus and Poisson ratio, were applied in order to determine the critical thrust force values. Empirical relationships between various feed rates and spindle rotational speeds with the drilling thrust force were established via regression analyses. These relationships would aid in predicting the critical feed rate while drilling the aforementioned composites. The results reveal that critical feed rate in between the range of 0.15–0.18 mm/rev was desirable for minimisation of the onset delamination damage on the composite laminates. However, the stiffer crystalline structure of the flax fibres as compared to the synthetic fibres inflicted toward the presence of delamination damage below the critical feed rate and thrust force values.