Mechanical Performance and Drilling-Induced Delamination of Flax – Pineapple Natural Fibre Reinforced Polymer Composites

This study investigates the mechanical properties and drilling delamination of hybrid naturalfibre-reinforced polyester composites using bidirectional flax and pineapple leaf fibre (PALF) mats for sustainable semi-structural applications. Four laminates were fabricated by hand layup: pure pineapple (PPP), pure flax (FFF), and two hybrid laminates (PFP and FPF). Tensile, flexural, impact, hardness, density, and water absorption tests were conducted to evaluate their performance. The effect of tool diameter, spindle speed, and feed rate on drilling-induced delamination was investigated using a Taguchi-based experimental design. The results showed that the FPF laminate exhibited the highest flexural strength (85.04 ± 7.46 MPa), whereas the FFF laminate demonstrated the highest tensile strength (50.86 ± 4.78 MPa) and the lowest water absorption (0.8686 ± 0.12%). Pineapple fibre-rich laminates (PPP and PFP) exhibited superior impact resistance (49.27 ± 6.06 J/m) and hardness (79.2 ± 0.74 Shore D). Machinability analysis indicated that feed rate is the most significant parameter influencing delamination, with minimum damage occurring at a feed rate of 0.05 mm/rev, moderate spindle speeds (800–1600 rpm), and smaller drill diameters (2 mm). The findings demonstrate the potential of hybrid natural fibre composites for sustainable semi-structural applications and provide guidance for the machining of such materials.