In this study, flexural characteristics of low-density polyvinylchloride foam core sandwich structures consist of carbon fibre/epoxy facings hybridised with very thin stainless-steel wire mesh sheets were investigated. A comprehensive work was conducted considering the following design parameters: core thicknesses, wire mesh sizes, stacking sequences of wire mesh sheets and support span lengths for flexural tests. During the evaluation of flexural characteristics, experimental ASTM standards (C393, D3039, D7249 and D7250) were utilised. In addition, experimental flexural stiffness values were compared to analytically obtained results. By hybridisation of carbon fibre/epoxy facings with wire mesh sheets, significant improvements in flexural characteristics of sandwich structures were obtained. Besides improving bending behaviour and the larger amount of load-carrying capacity even at the same deflection values, the sandwiches with wire mesh sheets also prevented catastrophic sudden failure, which is the common case for carbon/epoxy/polymer foam core sandwiches. Response surface methodology was applied to evaluate the effects of the design variables on the load capacity of the sandwiches, and optimal solutions were revealed. The developed sandwiches can be good candidates in applications where both high stiffness-to-weight ratio and resistance to sudden failure are desired.

Silicon dioxide (SiO₂) nanoparticles can be used as reinforcing material for composites due to their favorable characteristics. However, they are commonly subjected to surface treatments with silane coupling agents to achieve fine dispersibility and better mechanical interlocking at interface. In this study, the silane-coated SiO₂ nanoparticles (as received) were used as secondary reinforcement without applying additional silane treatment process. KH550 and KH570 silane-coated SiO₂ nanoparticles were dispersed, respectively, into polymer matrix, and then the modified matrix was reinforced with glass fibers. Silanized SiO₂ filled glass fiber reinforced polymer (GFRP) nanocomposites were investigated for physical, mechanical, morphological, and thermal properties. Depending on the nanoparticles' ratio and silane coating, the increments were obtained till 10% for tensile strength, between 18.40% and 75.26% for flexural strength, and till 81% for impact strength. SEM confirmed that the enhancements could be attributed to the improved interfacial adhesion between the modified matrix and fiber reinforcements. The void contents within the polymer nanocomposites decreased by 38%–54% compared to a pure one. DSC and TGA examinations revealed that silanized SiO₂ nanoparticles provided a better curing behavior (10% increase in T_g for 3 wt.% KH550-SiO₂) and improved thermal stability for the GFRP composites (increase in T_end values by 50–70°C). Generally, KH550 silane-coated SiO₂ has provided enhanced interface strengthening, leading to better characteristics for GFRP composites since the amino functional groups contained in KH550 have more favorable integration with epoxy matrix.

In this study, c-BN nanoparticles were dispersed into epoxy at various contents and then reinforced with carbon FRP. The presence of c-BN nanoparticles provided to obtaining lower voids within the laminate, improved interfacial adhesion, and better load transfer between the carbon fibers and matrix. The findings showed that c-BN-filled carbon FRP composites enhanced the tensile strength and impact toughness by 20% and 42%, respectively. Although the flexural strength values decreased, the flexural behaviors were improved by preventing the sudden fractures. Higher decomposition and increased glass transition temperature (T_g) values (16.09% to 21.14%) have been obtained, leading to better thermal stability. Graphical Abstract

Developments for improving the effectiveness of the composite structures strongly depend on the manufacturing methods. Additionally, the composite manufacturers have put effort into cost-effective and automated fabrication with mechanization. Controlling of the imperfections is also an important consideration for the production. This study presents several manufacturing methods for fiber-reinforced polymer composites. It also draws attention to novel techniques that use advanced technology required for the developed composite designs. Besides the conventional methods such as hand lay-up, vacuum bag, resin transfer molding, resin infusion, and autoclave, the advances in hot press molding, pultrusion process, and automated lay-up method were indicated. Moreover, the methods making difference for the hybrid composite designs such as the same qualified resin transfer molding and automated stitching processes were introduced. The advantages and limitations were indicated for the manufacturing methods and the usage purposes were addressed.