Drilling Parameters and Post-Drilling Residual Tensile Properties of Natural-Fiber-Reinforced Composites: A Review

This review highlights the influence of parameters on the drilling characteristics of biocomposites including natural fibers. The particular structure of natural fibers, including their hierarchized geometry, which potentially causes fibrillation, can result in an increased chance of irregularity of the hole and a more complex mode of delamination or, in general terms, damage to the composite. On the other hand, to attain an effective junction of the laminates in a structure, a nut-bolt procedure must be selected, which requires the performance of a drilling operation. This is becoming increasingly important since the fields of application for natural fibers and their variety have been steadily growing in the last few decades. Additionally, adequately performed drilling operations can address considerations related to circular economy. The drilling characteristics evaluated herein include thrust force, torque, surface roughness, and the delamination factor at the entry and exit of the drilling tool. The variation in tensile strength, stiffness, and strain propagation due to the presence of open holes of various sizes, the number of holes, the holes' patterns, the effect of the type of fiber of the notches, the fiber architecture, and the fibers' stacking sequence in biocomposites have also been discussed.