Influence of environmental conditioning on mechanical properties of carbon dry fibre preformed thermoplastic matrix composites manufactured via automated placement-resin infusion process

In the present work, dry fibre placement (DFP) of co-polyamide based carbon fibre spreadtow bindered tape for fabrication of thermoplastic acrylic resin composites was explored. The DFP followed by vacuum assisted liquid resin infusion (LRI) is expected to be an alternative process to traditional preforming approaches. This research work looks at the influence of water immersion on the performance of the composites was studied. The thermo mechanical behaviour of the aged and unaged samples were carried out as a function of temperature. The flexural strength of aged samples dropped by 4 and 17% after one and three months respectively. However, no significant changes were observed in flexural modulus compared to unaged. The interlaminar shear strength decreased by 19% and 35% after one month immersion and three months immersion. The results were complimented by fractographic and morphological studies

Analysis of failure modes for a non-crimp basalt fiber reinforced epoxy composite under flexural and interlaminar shear loading

This study investigates the mechanical properties (inter laminar shear and flexural strength) and failure modes of a basalt/epoxy composite, manufactured using a non-crimp-fabric (NCF) with vacuum assisted resin infusion process. Under flexural bending, damage initiated on the compression side between 20 and 50% of peak load and progressed from ply to ply with increasing load. Failure at tension surface of the flexural bending specimen was confined to the bottom ply and was evident only close to final failure. Fibre kinking was the dominant failure mechanism on the compression side whereas fibre breakage was the dominant mechanism on the tension side. Regarding interlaminar shear, interlaminar shear cracks initiated once samples were subjected to stress levels above 50% of peak stress and grew until failure with the crack following the fibre matrix interface of 90 degree tows. Overall, comparing with values available in the open literature, the NCF basalt/epoxy composite outperformed plain-woven basalt/epoxy and plain-woven E-glass/epoxy composites in terms of both flexural and interlaminar shear strength but demonstrated lower strength than NCF E-glass/epoxy composite

Flexural properties and failure mechanisms of infusible thermoplastic-and thermosetting based composite materials for marine applications

This study aims to evaluate the flexural properties and associated failure mechanisms of a reactive thermoplastic relative to traditional thermosetting resin systems (polyester, vinylester, epoxy) for potential application in marine vessels over 50 m in length, as part of the H2020 FIBRESHIP project. All resin systems are compatible with the vacuum assisted liquid resin infusion manufacturing technique commonly used in small/medium size shipyards. Glass fibre reinforced polymer (GFRP) laminates were manufactured, test samples extracted, immersed in deionised water or an organic liquid (diesel) and mechanically tested to evaluate the flexural strength and modulus. Failure mechanisms are analysed by scanning electron microscope (SEM). In terms of flexural strength, the reactive thermoplastic based laminate performed similar to the epoxy in terms of retained strength in both deionised water and diesel. The governing failure mode of fibre buckling and kink band formation coupled with interlaminar cracking was identified for both the epoxy and the thermoplastic. The vinylester laminate retained equivalent strength in all three environments while polyester showed the greatest reduction in water due to extensive interlaminar cracking. Overall, the flexural properties of the reactive thermoplastic are shown to be competitive with traditional candidate resin systems for marine structures. The strength reduction and failure modes in the dry, wet and diesel condition were similar to the epoxy while the reduction of modulus was negligible in water and less than 10% in diesel

Comparative evaluation of vat photopolymerization and steel tool molds on the performance of injection molded and overmolded tensile specimens

This study explores the use of vat polymerization stereolithography (SLA) for fabricating mold tooling, subsequently utilized in injection molding (IM) and overmolding of tensile specimens and directly compared to those produced using metal molds. The results first find the manufacturing time for an SLA-fabricated mold is remarkably short, approximately 6 h, presenting a substantial improvement over traditional methods. Mechanical testing revealed that the tensile specimens from the SLA-fabricated molds exhibited the highest tensile strength among all overmolding batches. This performance was consistent with the tensile bars produced using metal molds, demonstrating the viability of SLA-fabricated molds for overmolding applications and highlighting the potential of FDM to customize the properties of final products. However, variations in mold types impacted the dimensional tolerance and tensile strength of the final specimens. Metal moldfabricated tensile bars exhibited superior dimensional accuracy and maximum tensile strength (50.6–61.7 MPa) compared to those produced with SLA-fabricated molds (46.9–55.9 MPa). These differences are attributed to the rougher surface finish inherent to the layer-by-layer construction of SLA and the internal stresses and defects resulting from lower thermal conductivity and uneven cooling. In conclusion, this study underscores the promising future applications of SLA-fabricated molds in overmolding, offering reduced manufacturing costs and enhanced design freedom. The findings support the potential of SLA to revolutionize mold fabrication, thereby extending its utility and optimizing the production of polymer components with customized properties.</p

Mechanical evaluation and failure analysis of composite laminates manufactured using automated dry fibre tape placement followed by liquid resin infusion

Automated tape placement is seen as a promising technique for the manufacture of net-shape dry fibre preforms using carbon fibre tapes. However, most of the dry fibre tapes (DFT) available on the market are proprietary and aimed mainly at the aerospace sector. In the current study, two different binders (polyurethane and phenoxy water based binder) were used to coat and hence stabilise the carbon fibre tows. A net shaped preform was manufactured using Laser-Assisted Dry Fibre Tape Placement (LDFTP) and subsequently infused by vacuum assisted liquid resin infusion. The mechanical properties of the resulting laminates were compared to the laminates where the preform was manually laid up by hand with and without a coating (baseline). Failure mechanism analysis was carried out using scanning electron microscopy (SEM). The LDFTP process improved cured ply thickness (17–20% reduction) and fibre volume fraction (+9%). Interlaminar shear strength (ILSS) showed a significant improvement of 35–48%. However, only laminates manufactured using phenoxy coated LDFTP manufactured preforms showed comparable flexural strength to the uncoated baseline. Flexural modulus reduced in all cases. Further optimisation of binder content and process parameters (layup rate, consolidation temperature) is required for high speed deposition, better consolidation and improvements in mechanical properties