Mechanical and moisture diffusion behaviour of hybrid Kevlar/Cocos nucifera sheath reinforced epoxy composites

The aim of this research is partial replacement of plain woven Kevlar 29(K) with naturally woven cocous nucifera sheath (CS) waste. Laminated K/CS reinforced epoxy hybrid composites were fabricated by hand lay-up method followed by hot compression moulding with 105 °C temperature at 275 bar pressure for 1 h. The total fibre loading of the hybrid composite was maintained 45 wt.% and the ratio of Kevlar and Cocous nucifera sheath varies in weight fraction of 100/0, 75/25, 50/50, 25/75, and 0/100. Mechanical (tensile, flexural, impact), moisture diffusion and morphological behaviour of the laminated composites were evaluated. The results showed that the hybrid composites (75/25) declined the tensile strength by 19% compared to Kevlar fabric reinforced epoxy composites. But, the hybrid composites (75/25) exhibited highest flexural strength (175 MPa) and flexural modulus (18 GPa) than pure Kevlar reinforced epoxy composites. Moreover, the impact toughness of hybrid composites (86 kJ/m2) at 75/25 wt.% showed good agreement with the pure Kevlar fabric reinforced polymer composites (90 kJ/m2). From the moisture diffusion analysis, hybrid composites (75/25) exhibited better moisture resistance. Statistical analysis of the results has been carried out using one way-ANOVA (analysis of variance) and it shows that there is a statically significant difference between the obtained mechanical properties of the laminated composites. Morphology of the tensile fractured laminates showed the delamination's, matrix cracking and fibre/matrix adhesion. From the results, it has been concluded that naturally woven Cocos nucifera sheath has the potential to replace Kevlar fabric in the polymer composites exclusively for defence applications

Effects of layering sequence and gamma radiation on mechanical properties and morphology of Kevlar/oil palm EFB/epoxy hybrid composites

The present study evaluates the tensile and flexural properties, including the morphological features of gamma radiated Kevlar/oil palm empty fruit bunch (EFB)/epoxy hybrid composites fabricated using hand lay-up method with different layering sequences. The fabricated hybrid composites were exposed to different gamma radiation doses: 25 kGy, 50 kGy and 150 kGy. Mechanical (tensile and flexural) and morphological properties were evaluated by using universal testing machine and scanning electron microscopy, respectively. Results obtained indicated that tensile strength of hybrid composites were effected by layering sequence. The layering sequence involving the use of EFB as core material yielded better mechanical performance compared to the layering pattern when Kevlar served as the core material. The tensile and flexural properties of hybrid composites showed an improvement for irradiated samples at a low radiation level. Hybrid composites displayed decrease in tensile strength at 50 kGy whereas flexural strength still showed an improvement. However, at 150 kGy, the tensile and flexural properties exhibited significant degradation. FESEM of tensile fracture composites showed the exist of fibre pull out and voids. However, at 150 kV bigger and ruptured voids were observed. It can be concluded from this finding that mechanical performance of Kevlar/EFB/Kevlar hybrid composites after Gamma radiation, has made it as promising material for automotive, aerospace and construction applications

Development and characterization of Kevlar/Cocos nucifera L. Sheath/epoxy hybrid composites and graphene nanoplatelet- modified hybrid nanocomposites for ballistic applications

Kevlar 29 is the most widely used body armor material, since it possesses higher impact resistance compared to other man-made synthetic fibers, such as carbon, glass, etc. Even though Kevlar fabric provides an acceptable range of protection, it is not biodegradable and its manufacturing process is very harmful to the environment. This research has focused on evaluating the effect of hybridizing natural fiber with Kevlar 29 and the influence of adding GNP (Graphene nanoplatelets) on the mechanical, moisture diffusion, morphological, structural, ballistic performance, thermal degradation and viscoelastic properties of laminated composites. Through AHP (Analytical hierarchy process) method, naturally woven novel Cocos nucifera sheath (CS) was identified as a potential natural fiber to be hybridized with Kevlar for body armour applications. Laminated composites were fabricated by incorporating Kevlar and Cocos nucifera sheath layers in the epoxy matrix through hand lay-up method followed by hot pressing. GNP were added with epoxy through ultrasonication process. The mechanical, ballistic, thermogravimetric and dynamic mechanical testing’s were performed as per international standards. The mechanical and moisture diffusion properties analysis revealed that the hybrid Kevlar/CS (75/25) composites exhibited better mechanical and moisture resistance behavior among the hybrid composites. Moreover, addition of GNP improved the tensile, flexural, impact and interlaminar shear properties of laminated composites. However, optimal wt. % of GNP varies with different laminates. Moisture diffusion analysis showed that the laminates with 0.25wt % of GNP content efficiently hinder water uptake by closing all the unoccupied pores inside the laminate. Morphological investigations (SEM and FESEM) have proven that addition of GNP improved the interfacial adhesion and dispersion. Structural (XRD and FTIR) analysis reveals that at 0.25wt% of GNP, all the hybrid composites have shown better crystallinity index and the functional groups presents in the GNP can form a strong interactions with the fibers and matrix. The obtained ballistic results revealed that hybrid composites and CS/epoxy composite panels exhibited similar energy absorption and ballistic limit compared to Kevlar/epoxy composites due to CS’s chemical composition, architecture, and unique shock wave dissipation mechanism. Moreover, addition of GNP improved the energy absorption by 8.5% (nine plies) and 12.88% (12 plies) and the ballistic limit by 4.28% (nine plies) and 6.17% (12 plies), respectively of Kevlar/epoxy/GNP composites at 0.25 wt. %. However, hybrid Kevlar/CS/epoxy/GNP composites and CS/epoxy/GNP laminated composites didn’t show significant improvement after adding GNP. The obtained TGA results showed that Kevlar/CS (75/25) hybrid composites exhibited comparable thermal stability with Kevlar/epoxy composites. Differential scanning calorimetry (DSC) results revealed that hybrid composite offers a virtuous resistance or stability towards heat in the epoxy composites. Viscoelastic analysis results showed that the storage modulus (E’) and loss modulus (E”) of Kevlar/CS (75/25) hybrid composites were higher among the laminates due to improved interfacial interactions and effective stress transfer rate. Also, inclusion of GNP enhanced the thermal stability and viscoelastic properties of hybrid composites due to effective crosslinking which improves the stress transfer rate. Hence, this new ecofriendly material (Cocos nucifera sheath) will efficiently replace Kevlar fabric in the protective applications

Advancement in fiber reinforced polymer, metal alloys and multi-layered armour systems for ballistic applications – a review

The recent research and development performed for armour systems for material selection and analysis has helped discover new and significant material properties suited for ballistic applications. The realm of ballistic studies has employed advanced materials to provide the desired performance, considering the strict requirement of perfect material selection for armour systems. Energy absorption, ballistic limit, and depth of indentation are the most important parameters to be analyzed for an efficient armour system. The importance of utilizing appropriate materials for armour system is necessary, to achieve higher energy absorption, ballistic limit, and low blunt trauma (<44 mm), while simultaneously ensuring the armour has low weight. The aim of this review is to analyze the different armour systems such as fiber reinforced polymeric composites, metallic and multilayer armour systems (MAS) to understand their response on ballistic impact. Also, the importance of advanced fabrication techniques such as bio-inspired fabrication and additive manufacturing for armour applications has been addressed in detail. Moreover, this review critically analyzed the possible ways to enhance the ballistic performance of fiber reinforced polymeric composites, metallic materials, and MAS

Selection of natural fiber for hybrid kevlar/natural fiber reinforced polymer composites for personal body armor by using analytical hierarchy process

Kevlar 29 is the most widely used synthetic fiber for body armor applications and they have been derived from petroleum based resources. Depletion of petroleum resources and the increase in awareness about the eco-friendly materials encouraged the researchers to explore the potential use of natural fiber as an alternative for synthetic fibers. Hybridization of natural fiber with synthetic fiber will result in unique properties which is difficult to obtain from the individual fibers. In this research Analytical Hierarchy Process (AHP) was used to identify the most suitable natural fiber to be hybridized with Kevlar 29 fiber as a reinforcement in the polymer composites for personal body armor. Fourteen natural fibers and seven criteria's were selected and analyzed for hybridization with respect to the personal body armors design specification. Cocos nucifera sheath which is a naturally woven fiber yields the highest priority vector and it was selected as a most promising natural fiber for hybridization with Kevlar 29 for personal body armor. Eventually, sensitivity analysis was carried out to check the stability of the priority ranking