Integrated multi-assessment and structural performance index framework for stacking-sequence optimisation of natural fibre reinforced laminates

Natural fibre-reinforced polymer composites (NFRPCs) are sustainable alternatives to synthetic laminates; conversely, their structural reliability is influenced by type of fibre, fibre orientation and stacking architecture. In this work, ten sample laminate configurations (S1-S10) with Flax (F), Hemp (H), and Kenaf (K) fibres were fabricated using a hand lay-up method with single-layer (SL), double-layer (DL), and alternating-layer (AL) sequences under 0/90° and ± 45° orientations. Mechanical properties, namely tensile, flexural, and compressive strengths, were experimentally evaluated. The double-layer 0/90° configuration (S7) demonstrated optimal mechanical performance, achieving Tensile, Flexural, and Compressive strengths of 57.13 MPa, 60.50 MPa, and 638.63 MPa, respectively. Shifts in the laminate orientation from 0/90° to ± 45° resulted in tensile reductions of up to 54%, thereby enhancing shear-dominated stress redistribution. A mechanics-informed Structural Performance Index (SPI) framework was developed, incorporating normalised tensile, flexural, and compressive responses into application-specific structural indicators. The SPI-based evaluation recognised S7 as the best arrangement for structural and crash-dominant scenarios (SPI = 0.99), whereas kenaf-dominant laminates (S5) were recommended for the stiffness-oriented applications. The proposed SPI methodology delivers a decision tool that associates experimental characterisation and reliability-driven laminate selection for multi-axial engineering applications.