High mineral-filler loadings can improve epoxy resistance to ignition and sustained burning but may impair impregnation and interlaminar performance in continuous-fibre laminates. This study examined an application-oriented carbon/epoxy configuration containing aluminium trihydroxide (ATH) at a 1:1 mass ratio relative to the combined resin-hardener system, corresponding to 50.0 wt.% ATH in the total uncured formulation and 130 phr relative to neat resin. Laminates were manufactured by the vacuum-free hand-lay-up route used for prototype electric-vehicle body panels. The objective was to quantify the mechanical-flammability-screening trade-off of the realised configuration rather than isolate an intrinsic ATH effect. Reference (C) and ATH-filled (AP) laminates used the same three-ply carbon-fabric architecture and base epoxy system. Tensile response was evaluated at -40, +20, and +100°C, together with unnotched Charpy impact toughness and apparent interlaminar shear strength (ILSS). Limiting oxygen index (LOI) and horizontal UL 94 testing provided flammability screening. AP showed 30-38% lower tensile strength and lower apparent tensile modulus. Normalised impact toughness was lower, but the difference was not statistically significant (p = 0.236). Apparent ILSS decreased from 48.14 ± 1.13 to 21.82 ± 5.37 MPa (-54.7%, p < 0.001). Because AP was thicker and had a lower apparent fibre volume fraction, mechanical differences are interpreted as configuration-level outcomes rather than an isolated ATH effect. LOI increased from 23.3 to 35.0% O₂, while AP did not ignite during the prescribed horizontal UL 94 exposure. These results define a high-loading boundary case for external prototype bodywork, not electric-vehicle fire-safety qualification.
This study presents a multifunctional bio-composite dual-layer 3D/4D printed composite system for customised protective equipment applications. It includes facial masks, forearm guards, and football shin pads classified as advanced 3D/4D printed orthoses/gear. The outer polylactic acid (PLA)/bamboo charcoal (BC)/continuous flax fibre (CFF) region provides structural reinforcement, while the flexible thermoplastic polyurethane (TPU)/BC/CFF inner region is intended to improve conformability and provide potential energy-dissipation capability. This is suitable for prolonged use in orthotic applications. All components are printed using fused filament fabrication and thermally activated above the glass transition temperature to enable 4D flexibility, energy absorption, shape programming, and multi-cycle reconfiguration directly on anatomical geometries through controlled programming using anatomical models. The mechanical, flame-retardant, and shape-recovery performance of the bio-composites are experimentally evaluated and integrated into an application-driven design framework. In addition, a cradle-to-grave and cradle-to-gate life cycle assessment is performed to evaluate the environmental footprint of the bio-composite systems and compare them with conventional petroleum-based PPE. The results demonstrate the feasibility of integrating complementary rigid and flexible bio-composite regions with thermally activated shape adaptability, while offering reduced GWP within the investigated life-cycle scenarios. As such, it represents a highly promising solution for next-generation orthoses/gear and orthotic devices.
Adhesive joints attract implementation in structural systems whose integrity depends on the strength and durability of bonded joints. Nanofillers are employed to reinforce adhesive joints for longer service life. This study investigates mechanical performance and failure mechanisms of polyurethane (PU)/α-zirconium phosphate (α-ZrP) nanocomposite adhesives using integrated finite element (FEM) and discrete element modelling (DEM) frameworks, validated against experimental measurements on aluminium–aluminium (Al–Al) single lap joints (SLJs) bonded with PU adhesive. FEM incorporates viscoelastic behaviour and cohesive zone formulation to predict stress-strain and load-displacement responses of PU/α-ZrP nanocomposite and Al–Al/PU SLJs. Sensitivity analysis of tensile strength simulations defined Poisson’s ratios of neat PU and 0.5 wt% PU/α-ZrP nanocomposite. Stress analysis of SLJs reveals pronounced peak stresses at overlap edges due to load-path eccentricity and adherend bending, while compressive stresses develop in the central bondline. Scalar stiffness degradation indicates neat PU exhibits distributed cohesive damage across ∼52% of the cohesive layer at 94% of maximum load. In contrast, α-ZrP-reinforced system confines damage to overlap edges, with only 13.8% of the bondline exceeding 90% damage; this indicates improved structural stability. DEM simulations using Johnson-Kendall-Roberts (JKR) cohesive model provided microscale insight into bond coordination and degradation, yielding particle-particle cohesion energy densities of 4 J/m2 and 5 J/m2 for neat PU and 0.5 wt% α-ZrP-reinforced PU, respectively. The reinforced system demonstrated reduced bond depletion and more stable contact evolution than neat PU. Experimental tensile and SLJ tests validated both FEM and DEM, demonstrating that integrated FEM-DEM enables multi-scale characterization of adhesive joint performance.
