Increase In Interlaminar Shear Strength Research Articles

Dodging reality, striking the virtual: An undulating strategy for effectively enhancing CF/PEEK interfacial adhesion!

The design of carbon fiber (CF)-reinforced polyetheretherketone (PEEK) composite materials with suitable interfaces has consistently been challenging. In this study, we sulfonated poly (phthalazinone ether sulfone ketone) (PPESK) and PEEK to prepare water-soluble SPPESK and SPEEK. Subsequently, we prepared a water-soluble sizing agent (SPPESK/SPEEK) via a straightforward blending process. This sizing agent tended to accumulate randomly on the surfaces of CFs, forming a thin film with a heterogeneous structure in the nanoscale. At the molding temperature of the composite material, the two components on the fiber surface exhibited different rheological behaviors, with PEEK preferentially infiltrating the SPEEK region, forming strong molecular entanglements. Meanwhile, the SPPESK region provided a rigid supportive structure, offering the potential for the mechanical interlocking of PEEK in the interface layer. The performance of the prepared composite materials was significantly enhanced, with their interlaminar shear strength and flexural strength reaching 87.1 MPa and 975.8 MPa, respectively. With respect to those of commercial fiber-reinforced PEEK composites, an 89.8 % increase in interlaminar shear strength and a 79.39 % increase in flexural strength were observed. This interface reinforcement mechanism presents a universally applicable strategy for the future development of fiber-reinforced composite materials.

Nano-engineered hierarchical natural fibre composites with localised cellulose nanocrystals and tailored interphase for improved mechanical properties

Natural fibre composites have been utilised in many applications such as automotive and buildings, thanks to their high specific properties and environmentally friendly nature. However, the incompatibility between hydrophilic natural fibres and hydrophobic polymer resins remains a longstanding issue in natural fibre composites. Inspired by nature's hierarchical structures and tailored functionalities, a nano-engineered hierarchical natural fibre composite has been developed in this study, utilising cellulose nanocrystals (CNCs) as localised nano-reinforcements at flax surfaces in a flax/bio-epoxy system. A simple and versatile spray coating technique was used to deposit CNCs on unmodified flax fibres, without using any chemical solvents. With the increased surface roughness and hence improved epoxy wetting on nano-engineered flax surfaces (3 wt% CNC loading), mechanical properties of the hierarchical composites have been significantly improved, with a 60 % increase in interlaminar shear strength, indicating an enhanced interfacial load transfer between flax and epoxy, alongside improved flexural modulus (14 %) and strength (23 %). This green approach without using any chemicals provides a scalable and sustainable way to develop tailored interfaces for natural fibre composites with enhanced resin wetting and mechanical properties.

Characteristics of in-situ automated fiber placement carbon-fiber-reinforced low-melt polyaryl ether ketone laminates part 1: Manufacturing influences

This study presents an investigation into mechanical and thermal properties, as well as the microstructure of Automated Fiber Placement-manufactured laminates using a novel carbon fiber-reinforced low-melt polyaryl ether ketone polymer material. The material’s lower melting temperature and lower melt viscosity as compared to established high-temperature thermoplastic materials as PEEK, promises favourable characteristics for the Automated Fiber Placement process. This work aims at in-situ consolidation and the influence of a heated tooling and a post process tempering step, which both turned out to be promising in previous investigations. Laminates were manufactured using a cold tooling, a heated tooling configuration, a cold tooling with a subsequent tempering process step and a hot-pressed reference laminate. Differential Scanning Calorimetry showed that crystallinity values more than doubled for the heated tooling and post process tempering configurations, compared to the cold tooling, reaching 24% and 30%, respectively. Mechanical strength values showed an increase in interlaminar shear strength and compression strength but did not increase to the same extent as was expected from the increase in crystallinity. With Scanning Electron Microscopy differences in the microscopic structure of the polymer matrix could be detected. While the post process tempering step leads to a mostly lamellar crystalline structure, the heated tooling configuration and the post process hot pressing induce a predominance of crystalline spherulites, which might positively affect the mechanical performance. Computed Tomography scans revealed a high amount of porosity in the in-situ-manufactured samples and unprocessed tape material, which likely mitigated the positive effect of increased crystallinity.

Enhancing interfacial solvent resistance and mechanical properties of carbon fiber/polyether ether ketone composites with water‐borne sizing agents based on cross‐linkable polyphthalonitrile

AbstractThe inherent structural properties and elevated processing temperatures of thermoplastic resins present new challenges in the realm of carbon fiber (CF) sizing agents. Consequently, a water‐based cross‐linkable nitro‐phthalonitrile capped polyfluorenyl ether ketone sizing agent was meticulously designed. The sizing agent exhibits superior storage stability, encapsulating particles spanning dimensions from 66.51 to 87.71 nm. The inherent mechanism during the hot‐pressing stage involves a self‐crosslinking of nitrile groups toward stable structures with unparalleled resistance to solvents. The crosslinked sizing agent boasts a remarkable glass‐transition temperature of 290°C. Noteworthy, significance is the consequential 40.1% augmentation in maximum flexural strength, along with a commendable 35% increase in interlaminar shear strength for CF‐1.5/PEEK composites in contrast to their unsized CF/PEEK counterparts. In summary, the focal aspiration of this research endeavor lies in offering a straightforward and viable methodology for the exploration of cross‐linkable sizing agents, strategically catering to both “thermoplastic processing” and “thermosetting applications.”Highlights Bulky fluorenyl unit increases the intermolecular volume of copolymer poly(fluorenyl ether ketone). The introduction of the BPF unit to the molecular elevates the thermal stability of the copolymer. Unique electron‐donating proclivity of the fluorenyl group drastically improved its reactivity. The polymerization was accomplished at a relatively low temperature of 150°C for practical applications. The ILSS, IFSS, and bending strength were noteworthy increased by 35%, 74.02%, and 40.1%

GO-tagged PEI sizing agent imparts self-healing and excellent mechanical properties to carbon fiber reinforced epoxy laminates.

Carbon fiber-reinforced epoxy (CFRE) laminates have attracted significant attention as a structural material specifically in the aerospace industry. In recent times, various strategies have been developed to modify the carbon fiber (CF) surface as the interface between the epoxy matrix and CFs plays a pivotal role in determining the overall performance of CFRE laminates. In the present work, graphene oxide (GO) was used to tag a polyetherimide (PEI, termed BA) containing exchangeable bonds and was employed as a sizing agent to improve the interfacial adhesion between CFs and epoxy. This unique GO-tagged-BA sizing agent termed BAGO significantly enhanced the mechanical properties of CFRE laminates by promoting stronger interactions between CFs and the epoxy matrix. The successful synthesis of BAGO was verified by Fourier-transform infrared spectroscopy. Additionally, the partial reduction of GO owing to this tagging with BA was further confirmed by X-ray diffraction and Raman spectroscopy, and the thermal stability of this unique sizing agent was evaluated using thermogravimetric analysis. The amount of GO in BAGO was optimized as 0.25 wt% of BA termed 0.25-BAGO. The 0.25-BAGO sizing agent resulted in a significant increase in surface roughness, from 15 nm to 140 nm, and surface energy, from 13.2 to 34.7 mN m-1 of CF. The laminates prepared from 0.25-BAGO exhibited a remarkable 40% increase in flexural strength (FS) and a 35% increase in interlaminar shear strength (ILSS) due to interfacial strengthening between epoxy and CFs. In addition, these laminates exhibited a self-healing efficiency of 51% in ILSS due to the presence of dynamic disulfide bonds in BAGO. Interestingly, the laminates with 0.25-BAGO exhibited enhanced Joule heating and enhanced deicing, though the EMI shielding efficiency slightly declined.

Fabrication and Performance of Continuous 316 Stainless Steel Fibre-Reinforced 3D-Printed PLA Composites.

This study investigates the feasibility of 3D printing continuous stainless steel fibre-reinforced polymer composites. The printing study was carried out using 316L stainless steel fibre (SSF) bundles with an approximate diameter of 0.15 mm. This bundle was composed of 90 fibres with a 14 μm diameter. This fibre bundle was first coated with polylactic acid (PLA) in order to produce a polymer-coated continuous stainless steel filament, with diameters tailored in the range from 0.5 to 0.9 mm. These filaments were then used to print composite parts using the material extrusion (MEX) technique. The SSF's volume fraction (Vf) was controlled in the printed composite structures in the range from 4 to 30 Vf%. This was facilitated by incorporating a novel polymer pressure vent into the printer nozzle, which allowed the removal of excess polymer. This thus enabled the control of the metal fibre content within the printed composites as the print layer height was varied in the range from 0.22 to 0.48 mm. It was demonstrated that a lower layer height yielded a more homogeneous distribution of steel fibres within the PLA polymer matrix. The PLA-SSF composites were assessed to evaluate their mechanical performance, volume fraction, morphology and porosity. Composite porosities in the range of 2-21% were obtained. Mechanical testing demonstrated that the stainless steel composites exhibited a twofold increase in interlaminar shear strength (ILSS) and a fourfold increase in its tensile strength compared with the PLA-only polymer prints. When comparing the 4 and 30 Vf% composites, the latter exhibited a significant increase in both the tensile strength and modulus. The ILSS values obtained for the steel composites were up to 28.5 MPa, which is significantly higher than the approximately 13.8 MPa reported for glass fibre-reinforced PLA composites.

Mechanical property enhancement of graphene-kenaf-epoxy multiphase composites for automotive applications

Kenaf composites have a high strength-to-weight ratio, but weak fiber–matrix interface bonding limits their automotive use. To address this, a novel technique was developed to fabricate multiphase composites using graphene nanoplatelets (GNPs), kenaf fibers, and an epoxy matrix. The composites were made using vacuum infusion molding, with the GNPs exfoliated using a bath sonicator for uniform dispersion. The composites modified with 0.2 wt% GNP showed the most significant improvement in mechanical properties. Specifically, these composites exhibited a 30.5% increase in tensile strength, a 61.5% increase in tensile modulus, a 17.6% increase in flexural strength, a 22.7% increase in flexural modulus, a 35.1% increase in interlaminar shear strength, and a 17.1% increase in fracture toughness. Additionally, the water absorption resistance of the multiphase composites improved by up to 7%. These improvements were attributed to the uniform dispersion of GNPs and improved interlocking with the fiber surface. The developed composite has the potential for interior parts (such as dashboards, interior walls, and luggage compartments) in the automotive vehicle.

Study on the heating mechanism and macro/micro properties of composite materials under microwave curing

AbstractCompared to composite components prepared by traditional thermal process, microwave‐cured laminates exhibit superior mechanical properties under the same heating cycle, indicating a unique heating mode that differs from air circulation. To progressively replace the thermal curing process with microwave technology in the aerospace composites manufacturing field, it is crucial to elucidate the heating mechanism of microwave‐cured composite materials. In this study, the microwave absorbing performance of both carbon fibers and epoxy resins was systematically compared and revealed. Drawing upon principles of organic chemical reaction and Fourier transform infrared spectroscopy, the results demonstrated the swift response of carbon fibers to microwaves, which facilitated heightened functional group transformation and more complete curing reactions at the fiber‐matrix interface. Notably, as indicated by the results of the three‐point bending tests and fiber push‐in tests, microwave‐cured laminates displayed enhanced interlaminar and interfacial bonding properties in comparison to thermally cured counterparts, resulting in a 10.74% increase in interlaminar shear strength (ILSS) and a 20.23% rise in interfacial shear strength (IFSS).Highlights Carbon fibers exhibits a more pronounced ability to absorb microwaves than resins. Microwave‐cured laminate achieves a higher degree of curing reaction. Microwave curing enhances the ILSS and IFSS of composite materials.

Fusion-bonding performance of short and continuous carbon fiber synergistic reinforced composites using fused filament fabrication

In this work, short and short continuous fiber synergistic reinforced composites (S-CFRPCs) were successfully fabricated by fused filament fabrication. The influences of short fiber content on the filament bonding properties were evaluated through short beam shear (SBS) and in-plane tensile shear tests. The data showed an increasing and then decreasing trends of interlaminar shear strength (ILSS) and in-plane shear strengths of S-CFRPCs specimens as short fiber content rose from 0 wt% to 10 wt%. Specimens with a short fiber content of 5% displayed higher load carrying capacities and significant fusion-bonding performances, with approximately 41% and 80% increase in ILSS and in-plane shear strength when compared to 0% specimen, respectively. The fracture surfaces of tested S-CFRPCs specimens indicated fiber pull-out and resin fracture as dominant bonding failure models. The use of proper amounts of short fibers effectively improved the fusion-bonding of S-CFRPCs. In sum, these findings look promising for future design of strong and tough composite structures.

An investigation to enhance the mechanical property of high‐performance thermoplastic composite through different plasma treatment

AbstractIn this study, polyetherketone was investigated as the high‐performance thermoplastic resin for fabrication of carbon fiber reinforced polymer composite. The composites were manufactured by film‐fiber stacking process and consolidation by compression molding. The surfaces are modified with different plasma treatment (argon, nitrogen, and air) to overcome the inert nature of carbon fiber surface and subsequent changes were analyzed through atomic force microscopy, X‐ray photoelectron spectroscopy, and contact angle measurements. The effectivity of each type of plasma treatment in improvement of the surface—roughness, composition, and wettability were quantified and the subsequent effect on the mechanical properties was demonstrated by measurement of tensile properties and interlaminar shear strength (ILSS). The changes in interfacial morphology of the composite post plasma treatment have been characterized by scanning electron microscopy. From the test results, nitrogen plasma was found to most effective with a 43% increase in mean tensile strength and 25% increase in ILSS when compared to untreated composite.

Surface modification of carbon fibres with ammonium cerium nitrate for interfacial shear strength enhancement

An ongoing research focus in the carbon fibre (CF) field has been to identify a practical and more effective surface modification method for improving CF's interfacial adhesion and bonding capacity, which is vital for achieving high performance CF composites. In this research, carbon fibres were modified by using a new and facile treatment process in an aqueous solution of ammonium cerium nitrate (ACN) at a low temperature (20 °C–50 °C). The surface analysis results revealed that the ACN treatment imparted a combined effect of CF surface oxidation and cerium (IV)/(III) immobilisation on the oxidised CF surface through coordination bonds, leading to a significantly increased specific surface area, surface energy and surface reactivity. These new surface characteristics directly contributed to an improved CF interfacial adhesion and load transfer between the modified CFs and an epoxy matrix. The study demonstrated that under specified conditions, the new treatment method resulted in 304% increase in interfacial shear strength (IFSS) and 130% increase in interlaminar shear strength (ILSS) without any significant reduction in CF's mechanical properties. In comparison, the ACN modification yielded CFs with a much higher ILSS than the current industrial processes using electrochemical oxidation and sizing.

Electrostatic incitation on fiber surface for enhancing mechanical properties of fiber-reinforced composite

The excellent wettability contributes to the formation of mechanical interlocking morphologies at the interface as well as to the reduction of the internal defects in the composite for enhancing the mechanical properties of the fiber-reinforced composites. Herein, a facile and effective electrostatic method is proposed, where a small proportion of negative charges are merely sprayed on the fiber surface to modulate wettability. The results revealed that negatively charged fibers exhibit superior wettability for resin. Furthermore, the interfacial shear strength (IFSS) of the electrostatically treated T800H carbon fiber (T800H-ES)-based composite is 29.9% higher than that of the untreated-fiber composites. The improvement in interfacial properties is mainly ascribed to the formation of mechanical interlocking induced by surface charge-triggered Cassie-Baxter (CB) to Wenzel (WZ) transition of a liquid resin on the fiber surface, as verified by molecular dynamics (MD) simulations of carbon fiber–resin interfacial wetting. In addition, T800H-ES based composite has a 41.2% increase in tensile strength, a 22.5% increase in interlaminar shear strength (ILSS), and a 100.5% increase in fracture energy compared to as-received composite. These increases were mainly attributed to the improved interfacial adhesion and the reduction in internal composite defects. Consequently, this study reveals that the electrostatic charge-assisted wetting method is a green, cost-effective, and promising method for preparing composites with outstanding interfacial characteristics and mechanical properties.

An experimental investigation on impact dynamics response of woven roved glass fiber reinforced polyester laminated composites

AbstractThis research deals with the effect of stacking sequence over, the mechanical behavior of laminates that includes tensile, flexural, fractography, area of impact damage, and residual tensile strength. The angle‐ply laminate specimens were analyzed theoretically and correlated with experimental results. The highest interlaminar shear strength 32.89 MPa was exhibited by (60/30/60/30)S with better transverse stiffness of 444 N/mm. Among the developed laminates, (60/30/60/30)S showed the highest rate of residual strength degradation of 0.271. It has been found that an increase in interlaminar shear strength decreases the impact damage resistance of the composites. The angle‐ply laminate composites exhibited superior residual tensile and impact resistant properties when compared with uniply laminate composites.

Effect of addition of graphene nanoplatelets on the mechanical properties of triaxially braided composites

Braided composites possess an advantage of good out-of-plane mechanical properties, near net-shape manufacturing, impact and damage resistance. This work aims to investigate the effect of graphene nanoplatelet (GNP) addition on glass fibre triaxial braided composites (TBC). Tensile, flexural, and short beam shear tests were conducted to investigate the mechanical performance of the pristine and hybrid TBC. A numerical model was framed to estimate the material properties of hybrid TBC which were further used as input for the finite element simulation. Results indicate a 15% increase in tensile strength, a 20% increase in flexural strength and a 10% increase in interlaminar shear strength (ILSS). The experimental results were in good agreement with the analytical results. The braided architecture along with proposed GNP combination further enhances mechanical properties and enables gradual failure of the composite which is a desirable property for load bearing structures.

Enhanced interfacial adhesion of CF/PEEK-titanium hybrid laminates via introducing micro-nano layers with multi-walled carbon nanotube networks

An effective and easily-handled strategy for enhancing the interfacial adhesion of CF/PEEK-titanium hybrid laminates was proposed, which was achieved by introducing micro-nano layers with multi-walled carbon nanotube (MWCNT) networks between titanium and PEEK layers via electrophoretic deposition. The optimal deposition condition was explored by setting different concentrations of MWCNTs and times of deposition. Short beam shear tests were conducted at room temperature to characterize the interlaminar shear strength of the hybrid laminates. The results showed that the optimum parameters of deposition were 0.75 mg/mL of MWCNTs concentration and 90 s of deposition time, leading to a 47.8% increase of interlaminar shear strength compared with the sandblasted-only case. The mechanisms for enhancement were explained by micromorphology, apparent contact angle, and roughness analyses, which could be utilized to guide the preparation of CF/PEEK-Ti hybrid laminates with interfacial reinforcement by MWCNTs. Besides, multiple failure modes occurred at the metal-composites interface including a mixed mode of interfacial and cohesive failures, and a large amount of PEEK and carbon fibers remaining on the surface of titanium sheet proved the excellent interlaminar properties of the hybrid laminates.

Effect of material and processing parameters on fiber pinning effect and resultant interfacial bonding strength of CF/PEEK bilayer parts in overmolding process

The overmolding for thermoplastic composites is an integrated process that can manufacture multilayer parts with complex structures. However, the interfacial bonding strength between layers manufactured by different processes is weak. Here we study how material and process parameters affect the fiber pinning effect and thereby influence the interface binding strength of overmolded bilayer parts. The bilayer parts were prepared by overmolding the short-carbon-fiber-reinforced polyether-ether-ketone (SCF/PEEK) onto the hot-pressed woven-CF/PEEK (WCF/PEEK) laminates. An analytical model showed that the fiber pinning effect was dominated by the fiber content (Cf), interfacial temperature (Ti) and fiber orientation (αxx). The experimental results showed that a 32% increase in interlaminar shear strength (ILSS) of bilayer parts was achieved by regulating material and process parameters and optimizing the fiber pinning effect. The microstructural characterization shows that the Ti dominates the degree of resin fusion near the interface and thereby affects the fiber pinning depth indirectly. The Cf not only changes the amount of pinned fiber, but also affects αxx, which was confirmed by nano-CT scan.

Improved the surface properties of carbon fiber through hyperbranched polyaryletherketone sizing

AbstractA heat‐resistant soluble hyperbranched polyaryl ether ketone (HPAEK) is synthesized as the main resin of sizing agent and coated on the surface of carbon fiber (CF) with active group. As a result, the monofilament tensile strength of CF is increased by 12.00% and due to the improved fiber surface wettability and interface compatibility between CF and polyether ether ketone (PEEK), a 68.29% increase of interlaminar shear strength is achieved.

Simultaneous enhancement of mechanical and electrical/thermal properties of carbon fiber/polymer composites via SiC nanowires/graphene hybrid nanofillers

Carbon fiber (CF)/epoxy composites with hybrid nanofillers were prepared by electrophoretic deposition (EPD) of silicon carbide nanowires (SiCnws) on CFs, followed by in-situ grafting of graphene via chemical vapor deposition (CVD). The effects of SiC nanowires/graphene hybrid nanofillers on interlaminar shear strength (ILSS), flexural property, and through-thickness thermal conductivity of CF/epoxy composites were investigated. Due to the incorporation of SiCnws and graphene, the interfacial adhesion and the mechanical interlocking between CF and epoxy were improved significantly, resulting in an increase in ILSS and flexural strength. Moreover, the through-thickness electrical and thermal conductivity increased further with the increasing deposition time of graphene. It can be attributed to the hierarchical thermal conductive chains and networks that were formed by SiCnws deposited on the CF surface and the synergy between SiCnws and graphene. This strategy provides potential new ideas for the thermal management application of epoxy and its composites.

Enhanced interlaminar shear and impact performance of woven carbon/epoxy composites interleaved with needle punched high performance polyethylene fiber nonwoven

AbstractIn this study, high‐performance polyethylene (HPPE) fiber‐based needle punched nonwovens were interleaved in cross‐plied woven carbon fabric/epoxy composite laminates to enhance their interlaminar and impact properties. The placement of needle punched nonwoven interleaves exhibited considerable enhancement in interlaminar shear strength (ILSS), impact damage tolerance, and compression after impact (CAI) strength of laminates as evidenced by higher interlaminar strength, less absorbed energy, higher elastic energy, reduced damage degree, reduced out‐of‐plane deformation, higher load‐bearing capacity, and higher residual compressive strength as compared to control sample. In particular, the composite laminate with placement of interleaves in alternating sequence between carbon plies resulted in 205.76% increase in ILSS and 129, 103 and 85% increase in CAI at 10, 25, and 40 J impact energy, respectively. Moreover, damaged surface area and out‐of‐plane deformation reduced to 38.75% and 62.5%, respectively for the same specimen impacted at 40 J energy. These results suggest that the HPPE fiber‐based needle punched nonwoven interleaving can be adopted as a simple and low‐cost approach compared with other interleaving techniques, to enhance the resistance to delamination, impact performance, and damage tolerance of traditional structural laminates.

Simultaneously improved mechanical and electromagnetic interference shielding properties of carbon fiber fabrics/epoxy composites via interface engineering

Carbon fiber reinforced composites (CFRC) are in huge demand in aviation industry for reducing the fuel consumption, despite the unfavorable electromagnetic interference (EMI) shielding property. In this work, carbon fiber fabrics (CF) were coated by a thin layer of nickel (Ni) using electroless plating to increase the electrical conductivity of the composites. Dopamine was then self-polymerized on Ni coated CF (CF-Ni) surfaces to enhance the interfacial interactions between fibers and epoxy matrix. The results showed that the introduction of 0.39 wt% of polydopamine (PDA) content leads to a significant increase of interlaminar shear strength (ILSS), tensile strength and modulus by 70.7%, 22.7% and 15.3%, respectively, compared with CF-Ni/epoxy composites with free of PDA. The dominant facture mechanisms changed from fiber pulling-out and/or debonding to fiber breakage after the introduction of PDA. Compared with CF/epoxy composites, the EMI shielding effectiveness (SE) of CF-Ni/epoxy composites increased by 77.2% and slightly decreased with the increase of the PDA content. In order to further optimize the overall performances of the composites, the laminates structures were specially designed by replacing 2 plies of CF-Ni-PDA with CF-PDA in the middle according to EMI shielding mechanisms. The composites with special laminate stacking exhibited outstanding ILSS (61.2 MPa) and EMI SE (31.0 dB), which are dominant over most reported structural composites. The effects of humidity on the mechanical and EMI shielding properties were evaluated as well, indicating that the composites played a huge application potential in aircraft.