To address the interfacial failure caused by insufficient interlaminar bonding in Carbon Fiber Reinforced Polymer (CFRP) composites, an effective electrospinning technique is proposed to prepare the Polyethylene-co-Maleic Anhydride (PEMA) modified Polyvinylidene Fluoride (PVDF) fibers on CF fabrics to improve the flexural performance. Testing results show that the prepared PVDF fibers had various diameters varying from several hundred nanometers to several micrometer and were disordered to form semi-bonded PVDF-CF integrated structure. CFRP composite with PVDF areal density of 0.16 g/m² yielded the greatest flexural strength of 888.24 MPa and post-impact residual flexural strength of 122.05 MPa, exhibiting 25.1% and 68.6% increments respectively. Fiber trunks of PVDF were relatively stable and fiber ends were free-moved, which made them easier to construct fiber bridging network in situ compared with the fiber agglomeration of directly introducing fiber. The PVDF fibers bridging network at the interlayer could improve brittle epoxy resin, embed interfacial transition region and even penetrate adjacent CF, forming a three-dimensional interlocking that suppressed micro-crack generation and propagation. This contributed to failure modes changing from delamination dominated failure of unreinforced CFRP composites to shear-dominated failure of PVDF-reinforced composites. Overall, electrospinning method could provide an important alternative for manufacturing high-performance laminated FRP composites in industrial field.

This study focused on the various surface treatments of grinding, NaOH etching, HCl pickling, micro-arc oxidation and anodic oxidation to strengthen adhesive bonding joint of Aluminum (Al) substrate and Carbon Fiber Reinforced Plastics (CFRP). Different surface conditions were created by these treatments and simple Resin Pre-Coating (RPC) technique was further used to reduce the potential void defects at the root of those micro-cavities. Carbon Nanotubes (CNTs) were guided into the etched micro-cavities to construct quasi-Z-directional fiber bridging and form the "CNT-reinforced epoxy-pins”. The surface performance testing results imply that anodic oxidation of Al substrate created relatively even and continuous channels with higher hardness and better wettability among these treatments, which could provide quasi-vertical spaces for containing epoxy adhesive or CNTs. The single lap shear test results show combined treatments of anodic oxidation and upgraded RPC with CNTs technique on Al substrate yielded the highest bonding strength of 21.8 MPa (up to 243.3% greater than base strength). The constructed through-the-thickness "epoxy-pins” or "CNT-reinforced epoxy-pins” contributed to failure modes changing from complete debonding failure of Al substrate to peeled-off shallow fiber or delamination failure of CFRP panel. The combined treatments could be utilized to manufacture high-performance Al-CFRP composites for aviation industry application.

The high-performance Basalt Fiber Reinforced Polymer (BFRP) composites have been prepared by guiding Micro/Nano Short Aramid Fiber (MNSAF) into the interlayer to improve the resin-rich region and the interfacial transition region, and the flexible fiber bridging claws of MNSAF were constructed to grasp the adjacent layers for stronger interlaminar bond. The low-velocity impact results show that the MNSAF could improve the impact resistance of BFRP composites. The compression test results demonstrate that the compressive strength and the residual compressive strength after impact of MNSAF-reinforced BFRP composites were greater than those of unreinforced one, exhibiting the greatest 56.2% and 73.3% increments respectively for BFRP composites improved by 4wt% MNSAF. X-ray micro-computed tomography scanning results indicate that the “fiber bridging claws” contributed to better mechanical interlocking to inhibit the crack generation and propagation under impact and compression load, and the original delamination-dominated failure of unreinforced BFRP composites was altered into shear-dominated failure of MNSAF-reinforced BFRP composites. Overall, the MNSAF interleaving might be an effective method in manufacturing high-performance laminated fiber in industrial production.

The high-strength Basalt Carbon Fiber Reinforced Polymer (BCFRP) composites had been manufactured by guiding Imitating Tree-root Micro/Nano Aramid Short Fiber (IT-MNASF) into the interlayer of Basalt Fiber (BF) and Carbon Fiber (CF) plies to form thin interleaving, and various mass proportions of IT-MNASF were designed to discuss the reinforcing effect on the BCFRP heterogeneous composites. The results of three points bending tests showed that flexural strength and energy absorption of 4wt% IT-MNASF reinforced BCFRP heterogeneous composites had been improved by 32.4% and 134.4% respectively compared with that of unreinforced specimens. The 4wt% IT-MNASF reinforced BCFRP specimens showed both a greater strength and a lower cost (reduced by 31% around) than that of plain CFRP composites. X-ray micro-computed tomography scanning results exhibited that the delamination-dominated failure of plain BCFRP composites was changed into multi-layer BF and CF fabrics damage. The reinforcing mechanism revealed that the introduced IT-MNASF could construct quasi-vertical fiber bridging, and it was used as “mechanical claws” to grasp adjacent fiber layers for creating a stronger mechanical interlocking, and this effectively improved resin-rich region and interfacial transition region at the interlayers. The simple and effective IT-MNASF interleaving technique was very successful in low-cost and high-strength development of BCFRP heterogeneous composites.

Adhesively Bonded Carbon Fibre Reinforced Plastic (CFRP) and titanium alloy have been extensively used as a hybrid structure in modern aircrafts due to their excellent combination of mechanical properties and chemical stabilities. This study utilised NaOH anodising method to create micro-rough titanium surfaces for enhancing adhesive bonding between titanium alloy and CFRP laminates. A special and simple technique named Resin Pre-Coating (RPC) was also employed to improve the surface wetting of anodised titanium and grinded CFRP substrates. The influences of anodising temperature and duration on the surface morphology, wettability and adhesive bond strength were investigated. The single lap shear test results showed that the bond strength of specimens anodised at 20 ℃ for 15 min improved by 135.9% and 95.4%, respectively, in comparison with that of acid pickled and grinded specimens (without RPC treatment). Although increasing the anodising temperature and duration produced rougher titanium surfaces, the adhesively bonded joints were not strong enough due to relatively friable titanium oxide layers.

Basalt Fiber Reinforced Polymer (BFRP) composites have huge potential application respects for some civil fields due to enough strength/modulus to weight and low cost by replacing carbon fiber composites. Aiming at the issues in the Resin-Rich Region (RRR) and Interfacial Transition Region (ITR) of fiber reinforced polymer composites, the characteristic Aramid Pulp (AP) fibers with micro-fiber trunk and nano-fiber branches were manufactured into multiple non-woven ultra-thin interleaving at the interlayers of BFRP composites via compression molding to reinforce the flexural strengths and elastic moduli. AP fibers were introduced into RRR to form interleaving at the interlayer, the brittle epoxy adhesive layer was improved and enabled to avoid cracking under a low external load. Free fiber branches of AP were also embedded into BF layer to construct quasi-vertical fiber bridging behaviors in ITR, stronger mechanical interlocking was created to prevent crack propagation along the bonding interface of BF/epoxy. Three-point bending testing results showed the interleaving film with 4 g/m² AP exhibited the best effect among various areal densities and yielded average 315.75 MPa in flexural strength and 21.38 GPa in elastic modulus, having a 63.4% increment and a 47.1% increment respectively compared with the bases. Overall, the simple and low-cost AP interleaving is confirmed as an effective method in improving interlayer structure and flexural performance of BFRP composites, which may be considered to manufacture high-performance laminated fiber reinforced polymer composites in civil aviation industry.

Compressive strengths and elastic moduli of Carbon Fiber Reinforced Polymer (CFRP) composites can be noticeably improved by multiple ultra-thin interlays with non-woven Aramid Pulp (AP) micro/nano-fibers. 10-ply CFRP specimens with 0, 2, 4, 6, 8 g/m² AP were tested under uniaxial compression. Those flexible AP fibers, filling the resin-rich regions and further constructing the fiber bridging at the ply interfaces, can effectively suppress delamination growth and lead to very good improvements both in the compressive strength and the elastic modulus. The CFRP specimen with an optimum interlay thickness has a distinct shear failure mode instead of the typical delamination cracking along the direction of continuous carbon fibers. Compressive Strengths After Impacts (CAI) of 12.35 J were also measured, up to 90% improvement in CAI has been observed. It is concluded those ultra-thin interlays of non-woven AP micro/nano-fibers are beneficial to design and manufacture “high strength” CFRP composites.