David Ayre

This study provides a unified experimental comparison of 11 joint configurations in thick (7–12 mm) vacuum‐infused CFRP laminates, addressing a gap where individual reinforcement strategies have been studied in isolation but never benchmarked head‐to‐head under identical conditions. Layup architecture variants (baseline quasi‐isotropic, hard QI, soft QI, Double–Double), local reinforcement strategies (tow steering, concentric random mat tapering, random mat surface layers, metallic bushings), and hybrid or through‐thickness architectures (FiberJoints metallic–fiber patches, quadriaxial fabric, 3D woven angle‐interlock preforms). Double‐shear tests following ASTM D5961 were complemented by pulsed thermography and optical microscopy. The Hard QI + Taper configuration delivered the highest specific initial bearing load (196 kN/kg), followed by FiberJoints (181 kN/kg) and tow‐steered QI (161 kN/kg)—a 24%–50% improvement over baseline QI (130 kN/kg). FiberJoints provides independent validation of the Jakobsen et al. hybrid patch concept in a thick VARI laminate system. Quadriaxial laminates, though lower in specific initial strength (143 kN/kg), delivered record energy absorption (≈1140 J). Soft QI and Double–Double underperformed due to premature failure. Thermography discriminated between bearing‐, net‐tension‐, and shear‐out‐dominated failure mechanisms. These results establish quantitative benchmarks for reinforcement strategy selection in thick CFRP bolted joints.

This review paper explores the transformative potential of polymer composites and adhesives in reducing the weight of aircraft landing gear, thereby improving fuel efficiency and lowering emissions. The replacement of conventional metallic materials and mechanical fastenings with advanced thermoset/thermoplastic composites and adhesives can significantly enhance durability and performance in demanding operational environments. Unlike traditional fastening methods, the structural adhesives eliminate the weight penalties associated with mechanical fasteners, offering a lighter and more reliable solution that meets the rigorous demands of modern aerospace engineering. Furthermore, the review highlights a variety of manufacturing techniques and innovative materials, including bio-based polymers, self-healing materials, noobed composites, helicoid composites, and hybrid composites. The use of thermosets and vitrimers in adhesive bonding are presented, illustrating their ability to create robust and durable joints that enhance the structural integrity of landing gear systems. The paper also addresses current challenges, including recycling limitations and high material costs. Sustainability considerations, including the integration of self-healing materials, structural health monitoring systems, and circular economy principles, are discussed as essential for aligning the aerospace sector with global climate goals.

This study investigates the influence of limestone powder and metakaolin as sustainable eco-friendly additives on the properties and behavior of cementitious composite boards, with a focus on mechanical strength, physical properties, and microstructural characteristics. The experimental investigation begins with the characterization of the raw materials, including limestone powder, and metakaolin, to assess their particle sizes, elemental composition, and microstructural features. Cement composite boards were fabricated using an innovatively developed lab-simulated vacuum dewatering process, by varying the proportions of limestone powder and metakaolin as partial replacements for cement, along with waste kraft fibres as reinforcement. Mechanical testing was conducted to evaluate the flexural strength and behaviour of the composite boards according to standardized procedures. A microstructural analysis was performed using scanning electron microscopy (SEM) to examine the effect of additives on the cementitious matrix, fibrematrix interaction, and hydration products. The findings from the experimental study reveal insights into the influence of limestone powder and metakaolin on the mechanical properties and microstructure of waste kraft fibre-reinforced cement composite boards. Our analysis of the results shows that adding 9% limestone powder as partial cement replacement produces a 24% and 50% enhancement in flexural strength at 7 and 28 days of hydration, while that of metakaolin as partial cement replacement was optimum at 6% with an enhancement of 4% and 36%, respectively, at 7 and 28 days of hydration. The implications of these findings for the development of sustainable cementitious composite are discussed, including the potential benefits of using limestone powder and metakaolin as supplementary cementitious materials in waste kraft fibre-reinforced cement composite boards. Finally, recommendations for optimizing additive proportions are also provided to enhance the understanding and application of these materials in the construction and building industries.

Africa is the third-richest continent in the world in terms of bamboo species. Despite these laudable natural resources, most African countries still use asbestos cement board as one of their major building materials. This is chiefly due to the high cost of equipment and technologies associated with non-asbestos-fiber cement board production. The current research seeks to underscore the possibility of utilizing these massive continent resources for non-asbestos-fiber cement board production by employing the existing production process in the asbestos cement industries via an innovatively developed laboratory-simulated Hatschek process. Non-asbestos-fiber cement boards incorporating kraft and bamboo fibers were successfully produced in the laboratory using this innovative method based on Hatschek technology, with natural fibre addition in the range of 2–6 wt.%. Experimental results revealed that the Flexural strength and deflection of the board improved significantly, producing optimum values of 10.41 MPa and 2.0 mm, respectively for composite board reinforced with 10 wt.% and 6 wt.% of kraft pulp and bamboo fibers, respectively. The SEM morphology of the fractured surfaces revealed the mode of composite fracture as well as good interaction at the fiber–matrix interface. Overall, the mechanical properties of the developed composite boards satisfy the minimum requirements of relevant standards based on fiber cement flat sheets and can be employed for internal building applications in low-cost housing estates in developing countries. The outcome of this research indicates that the current industrial production process based on Hatschek technology can be employed for non-asbestos-fiber cement board production using the studied natural fiber.

Acoustic emission (AE) has received increased interest as a structural health monitoring (SHM) technique for various materials, including laminated polymer composites. Piezoelectric sensors, including PZT (piezoelectric ceramic) and PVDF (piezoelectric polymer), can monitor AE in materials. The thickness of the piezoelectric sensors (as low as 28 µm—PVDF) allows embedding the sensors within the laminated composite, creating a smart material. Incorporating piezoelectric sensors within composites has several benefits but presents numerous difficulties and challenges. This paper provides an overview of acoustic emission testing, concluding with a discussion on embedding piezoelectric AE sensors within fibre-polymer composites. Various aspects are covered, including the underlying AE principles in fibre-based composites, factors that influence the reliability and accuracy of AE measurements, methods to artificially induce acoustic emission, and the correlation between AE events and damage in polymer composites.

This paper presents a finite element model for predicting the performance and failure behaviour of a hybrid joint assembling fibrous composites to a metal part with reinforcement micro pins for enhancing the damage tolerance performance. A unit-strip model using the cohesive elements at the bond interface is employed to simulate the onset and propagation of debonding cracks. Two different traction–separation laws for the interface cohesive elements are employed, representing the fracture toughness properties of the plain adhesive bond and a pin-reinforced interface, respectively. This approach can account for the large-scale crack-bridging effect of the pins. It avoids using concentrated pin forces in the numerical model, thus removing mesh-size dependency, and permitting more accurate and robust computational analysis. Lap joints reinforced with various pin arrays were tested under quasi-static load. Predicted load versus applied displacement relations are in good agreement with the test results, especially for the debonding onset and early stage of crack propagation.