Improvement Of Interlaminar Shear Strength Research Articles

On the bending behavior of hybrid fiber–metal laminates (HFMLs) based on aluminum and glass/Kevlar fibers reinforced epoxy

In this work, the mechanical behaviors under flexural loading of fiber–metal laminates (FMLs) comprised of an aluminum alloy reinforced with glass fibers (GFs) and Kevlar fibers (KFs) embedded in an epoxy composite are experimentally investigated. For this purpose, non-FMLs, FMLs, and hybrid FMLs (HFMLs) are tested and their results are compared in terms of the flexural strength and modulus, strain to failure, toughness, interlaminar shear strength (ILSS), and specific properties. Results show that the incorporation of GFs on the compression side and KFs on the tensile side improves the bending properties of the HFMLs compared to the KF-based FMLs, which enhances the laminates’ resistance to bending loads. The HFMLs exhibit improvements of 24%, and 5% in flexural strength and modulus, respectively, compared to the KF-based FMLs. Moreover, hybridization significantly improves strain to failure by up to 115% compared to the GF-based FMLs. Additionally, the ILSS analysis reveals improved values in FMLs compared to non-FML samples, when GF-based FMLs demonstrate higher ILSS than KF-based ones, which can be attributed to GFs’ stiffness and high-quality bonding with the aluminum sheets. HFMLs attain a 19% improvement in ILSS compared to the KF-based FMLs. The failure mechanism depends on the intrinsic features of the studied fibers, while the studied FMLs display better damage tolerance. In this context, the HFMLs present enhanced toughness, delamination resistance, and the ability to prevent crack propagation, positioning them as promising candidates for lightweight structural applications where a balance between strength, stiffness, and toughness is required.

The effect of graphene oxide on thermal, electrical, and mechanical properties of carbon/epoxy composites: Towards multifunctional composite material

AbstractThe focus of this research work is to investigate the influence of graphene oxide (GO) on the mechanical, thermal, and electrical properties of carbon fiber‐reinforced polymer (CFRP) composites. The solvent mixing method with the new addition of a mixing stage is introduced for uniform distribution of graphene oxide in polymer. Different weight percentages of graphene oxide (1%, 1.5%, and 2%) were incorporated into the epoxy matrix, and the resulting composites were subjected to electrical conductivity, thermal conductivity, and interlaminar shear strength (ILSS) testing. The findings revealed a positive influence on material properties with the percentage of GO. Especially, the electrical conductivity and ILSS values reached up to 7.05 S/m and 11.03 MPa, respectively, when 1.5% GO by weight of the resin was added. The improvement in ILSS reported by 40% compared to the neat CFRP, and this increment was attributed to enhanced bonding between the epoxy matrix and carbon fabric. Maximum thermal conductivity of 1.04 W/m°K obtained at 1% GO filler, which is 15% higher than neat epoxy composite. Overall, these results illustrate the potential of GO as a promising filler to improve the electrical, thermal, and mechanical properties of CFRP composites. Proper optimization of graphene content in a polymer is needed to achieve the best multifunctional composite materials.Highlights The new solvent mixing method is introduced for uniform distribution of graphene oxide in polymer. Maximum thermal and electrical conductivity obtained at different percentages of graphene content in composite. Positive improvement is observed in mechanical, thermal, and electrical at a specific percentage of graphene in the composite. Proper optimization of nanofiller content in composite is needed to assess for maximum performance.

Biomimetic construction of 3D needle‐punched CF/PEEK composites based on ladybug forewing structure for directional reinforcement

Abstract3D needle‐punched CF/PEEK composites are a kind of composites with promising applications in multiple fields, such as implant materials, but their mechanical properties in the Z‐axis and interlaminar are still weak at present. In this study, a bio‐inspired reinforcement structure based on ladybug forewing was developed to achieve directed reinforcement of 3D needle‐punched CF/PEEK composites. Carbon fiber yarns were stitched into the 3D needle‐punched CF/PEEK preforms according to the set structure, and the bio‐inspired CF/PEEK composites were obtained after hot pressing. The interlaminar and in‐plane mechanical properties of the composites were investigated at different stitch lengths. The results showed that the addition of the bio‐inspired structure greatly improved the interlaminar shear strength of the composites, reaching 111.30 MPa, an enhancement of 95.06%. The in‐plane mechanical properties, including tensile, flexural, and compression, were also significantly improved to different degrees. The “structure‐effect” relationship in the bio‐inspired CF/PEEK composites was investigated, and the effectiveness of such a bio‐inspired reinforcement structure was demonstrated. This new reinforcement strategy provides a new idea for the improvement of the mechanical properties of multi‐stage carbon fiber‐reinforced thermoplastic resin matrix composites.Highlights The in‐plane and interlaminar mechanical properties of composites were simultaneously improved. Up to 95.06% improvement in interlaminar shear strength. A novel bionic strategy of directional reinforcement was developed. The “structure‐effect” relationship in the composites was investigated.

Lightweight, electrical insulating, and high thermally conductive all-polymer composites with reinforced interfaces

High thermally conductive materials with good electrical insulating and mechanical properties are indispensable for electronics. Aiming for all-polymer composites with light weight, electrical insulation and high thermal conductivity (TC), ultrahigh molecular weight polyethylene (UHMWPE) fibers/epoxy composites with two kinds of fiber orientation structures (0°/90°, ±45°) were fabricated by hot-pressing. It is found that the in-plane TC of ±45° composite is approximately 1.3–1.4 times that of 0/90° one, and the corresponding mechanism is verified by finite element simulation and model calculation. Thermally conductive pathways formed by UHMWPE fibers endow 0/90° and ±45° composites with the in-plane TC of 9.94 and 13.61 Wm−1K−1, respectively. Through depositing polydopamine (PDA) and grafting polyether amine (PEA) onto the surface of fibers, the poor fiber/epoxy interface was improved, resulting in 40.7% and 52.3% improvement in interlaminar shear strength (ILSS) and shear modulus, respectively. Simultaneously, a higher in-plane TC as high as 15.76 Wm−1K−1 is achieved. The heat dissipation evaluation indicates that the composite can reduce the temperature of the resistance wire by 14 °C. This work reveals the great potential of UHMWPE fibers in heat dissipation and provides a strong candidate for electrical insulating support materials with high TC for heat management of electronics.

Experimental and finite element study on high-velocity impact resistance and energy absorption of hybrid and non-hybrid fabric reinforced polymer composites

High-velocity impact resistance of FRP composites consisting of Kevlar, carbon and glass in hybrid and non-hybrid stacking sequences was studied through experimental and finite element analysis. Neat Kevlar/epoxy and Kevlar/glass/epoxy sandwich composites have the 1st and 2nd highest impact energy absorption percentage (100% and 97.99%, respectively). Carbon/epoxy composite exhibited the least energy absorption (38.78%). Other hybrid composites showed intermediate values of energy absorption in the range 38.58%–44.11%. Hybridization did not show any improvement in interlaminar shear strength of composites either. However, hybridizing Kevlar based composites with glass in the middle layer offered impact resistance close to Kevlar/epoxy composite while offering a 21% saving in material cost. Thus, such Kevlar and glass fabric-based sandwich composites possess a great potential as protective structures due to their ability to withstand impacts up to 200 m.s−1 velocity. These composites may also be considered for development of protective armor that are light-weight compared to conventional materials and more affordable. Finite element simulation results are in good agreement with that of experimental results with differences below 14%.

Enhancement of tensile, flexural and ILSS properties of C-epoxy composites with the addition of ETBN toughener and Af-MWCNTs

The objective of this research is to develop a hybrid composite with a unique combination of features such as tensile, flexural and Interlaminar shear strength (ILSS) properties. It is a present need for components used in underwater, aerospace, defence and automotive applications, as parts are subjected to a variety of loading conditions, including tensile, bending and shearing. Carbon fibre reinforced epoxy (C-epoxy) composite is modified by adding epoxy terminated butadiene acrylonitrile (ETBN) liquid rubber and amino-functionalized multi-walled carbon nanotubes (Af-MWCNTs). With the addition of ETBN, the tensile, flexural and ILSS properties were improved by 38%, 46% and 80%, respectively. The addition of 0.5wt% of Af-MWCNTs improved the tensile and flexural strengths by a maximum of 59% and 61%, respectively. In contrast, the maximum improvement in ILSS of 120% was obtained at 1.0 wt.% of Af-MWCNTs. The unique combination of C-epoxy-ETBN-Af-MWCNTs led to the formation of the serrated surface at the fibre matrix interface, which caused improved energy absorption. The toughening mechanisms which are responsible for the improvement in properties are discussed and the results are validated through finite element analysis (FEA).

MXene modified carbon fiber composites with improved mechanical properties based on electrophoretic deposition

To improve the weak fiber-matrix interface of carbon fiber composites, two-dimensional transition metal carbides or nitrides of MXene (Ti3C2Tx) nanosheets were introduced onto the surfaces of carbon fiber (CF) through electrophoretic deposition (EPD) technology for the first time. The MXene deposited CF was further infiltrated with epoxy resin by vacuum-assisted resin infusion (VARI) to fabricate CFRP composites. Results indicated that the MXene nanoparticles deposited on the surfaces of CF could significantly enhance fiber surface energy and wettability as well as surface roughness, which in turn remarkably increased the interfacial strength and flexural properties of fiber-resin. The MXene/oxidised CF/epoxy composites showed a 53% improvement in interlaminar shear strength (ILSS), a 22.2% enhancement in flexuous strength, and a 29.2% increment in monofilament tensile strength than non-functionalised specimens. This simple and effective strategy provided a promising approach for effective CFRP modification and continuous industrial production.

Improved mechanical responses of GFRP composites with epoxy-vinyl ester interpenetrating polymer network

Present investigation deals with development of glass fiber reinforced polymer (GFRP) composite with a matrix composed of a polymer blend of epoxy and vinyl ester. The evolved Interpenetrating polymer network (IPN) formed due to blending of the polymers resulted in improved tensile, flexural and interlaminar shear properties of the hybrid composite than that of both glass fiber/epoxy (GE) and glass fiber/vinyl ester (GVE) composites. Resin burn-off test revealed that the glass fiber volume fraction to be almost identical in all three composite laminates, which was ~45%. The role of curing temperatures (140, 170, 200 and 230 °C) on the cure kinetics of the composites was examined based on the flexural properties of the composites, which is also supported with the dynamic mechanical thermal analysis (DMTA) results. The glass fiber reinforced epoxy-vinyl ester interpenetrating polymer network (GEVIPN) composite led to 21.83%, 22.54% and 13.43% improvement in interlaminar shear strength (ILSS), tensile and flexural strength respectively, over GE composite at optimal post cure temperature. Further, chemical restructuring of GEVIPN composite was analysed by Fourier transform infrared spectroscopy (FTIR). From scanning electron microscopy (SEM), it was comprehended that strong interfacial bonding between the matrix and fiber made GEVIPN composite exhibit better mechanical properties.

Graphite fabric reinforced PAEK composites by novel impregnation-co-film technique

High performance polymers such as Poly(ether ether ketone) (PEEK), Poly(aryl ether ketone) (PAEK), Poly(ether ketone ketone) (PEKK), etc exhibit high melting points, 343 °C, 373 °C and 338 °C respectively and very high melt viscosity. They do not have appropriate solvents, which could open the ways to process their fabric reinforced composites; by impregnation technique followed by compression molding. Film stacking and powder sprinkling are the only possible techniques, which lead to weak crossover points due to non-wetting by the resin and finally resulting in inferior mechanical and interfacial properties and high amount of voids. In order to solve these problems, a novel technique called impregnation-co-film (ICF) is explored in this work. Polyetherimide (PEI) (10 wt% in dichloromethane solution) pre-impregnated graphite fabric prepregs were used before applying film technique followed by compression molding. The study compares properties such as density, void content, flexural strength, impact strength, Interlaminar shear strength (ILSS), thermal stability (in air) and interface by field emission scanning electron microscopy for the composite prepared with film stacking technique and that by impregnation-co-film stacking technique. It was confirmed that the new ICF technique proved to be significantly promising than the older technique almost in all aspects with 120% improvement in ILSS, 127% in flexural strength and 200% decrease in void content.

Effects of plasma treatment of carbon fibers on interfacial properties of BMI resin composites

High performance continuous fiber surface modification by inductively coupled RF plasma (ICP) and dielectric barrier discharge (DBD) low temperature plasma were conducted. X‐ray photoelectron spectroscopy (XPS) and other analytical testing methods systematically studied plasma treatment time, discharge power, discharge pressure, etc, on fiber surface state, surface composition, and surface shape changes in the appearance and wetting properties. The results show that after plasma treatment the surface of the fiber is grafted with a large number of polar functional groups such as carboxyl groups and hydroxyl groups. The surface roughness increases, the surface free energy increases, and the fiber wetting property is significantly improved, resulting in improvement in interlaminar shear strength (ILSS) between the fiber and the resin matrix. Finally, the surfaces of the fibers and its relationship with interfacial properties of fiber reinforced bismaleimide composites are also discussed.

Damage sensing in multi-functional hybrid natural fiber composites under shear loading

A comprehensive experimental study is performed to investigate the electro-mechanical response of jute/epoxy composites for in situ damage detection under in-plane shear loading conditions. By embedding carbon nanotubes (CNTs) in epoxy matrix and also reinforcing carbon fibers (CFs) using electro-flocking process between the jute laminates, a three-dimensional sensory network is generated inside the composites. A parametric study is conducted to examine the effect of two different weight percentages of CNTs (0.025% and 0.1%), two different CFs lengths (150 and 350 μm), four different CF flock densities (500, 1000, 1500, and 2000 fibers mm−2), and two different laminate orientations ((0-0-0-0)T and (0-90-0-90)T) on the generation of electrical conductive network and its role on damage detection. The electrical resistance values are measured using four circumferential ring probes measurement system. Results indicated that (0-0-0-0)T orientation showed 400% improvement in interlaminar shear strength compared to (0-90-0-90)T composites. CF flocking between the laminates experienced maximum increase of 50% in shear strength compared to non-flocked composites. For all composite types, there is no change in resistance during the elastic deformation of shear loading. Beyond elastic deformation, the increase in CF length and its density showed similar electrical response. The increase in CNTs concentration and laminate orientations did not show significant change in electrical response under shear loading conditions.

Augmenting mode-II fracture toughness of carbon fiber/epoxy composites through carbon nanotube grafting

Systematic experimental investigation is carried out to characterize the effect of carbon nanotubes (CNTs) grafting on the average mechanical properties and mode-II fracture toughness of carbon fiber reinforced plastics (CFRPs). Two growth strategies are used in a chemical vapor deposition (CVD) reactor to ensure uniform coverage of both sides of fiber fabric with CNTs. Improvement in interlaminar shear strength of CFRP due to incorporation of CNTs is found to be sensitive to the uniformity of grafted CNTs on the fabric surface. It is shown that the use of optimum CNT grafting strategy on the fiber surfaces leads to a significant improvement in flexural properties and mode-II fracture toughness of conventional CFRPs. However, the use of CNT grafted laminas in the composite laminate does not alter the response of CFRP under the uniaxial tensile loading. Scanning electron microscopy (SEM) analysis of failed composite coupons after mode-II testing reveals that different failure mechanisms operate in composite laminate fabricated with or without the use of CNT grafted laminas.

Improving the interlaminar shear strength and thermal conductivity of carbon fiber/epoxy laminates by utilizing the graphene‐coated carbon fiber

AbstractThe poor interlaminar properties restrict the application of carbon fiber reinforced polymer (CFRP) composites. In this work, a novel method for fabricating a graded interface structure is developed to improve the through‐thickness thermal conductivity of CFRP composites. High‐strength graphene nano‐plates (GnP) and phenolic resin (PF) were selected to deposit on the surface of carbon fiber to design a novel CF/Epoxy laminates, where a simultaneous improvement of interlaminar shear strength (ILSS) and through‐thickness thermal conductivity was observed. With addition of 1 wt % of GnP‐PF in CF, 37.04% increase of the ILSS, and 16.67% enhancement of thermal conductivity compared to the original CFRP. The mechanism for improvement of both ILSS and thermal conductivity was studied by scanning electron microscopy and nano‐indentation, where a better interface formed by GnP‐PF has been clearly observed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47061.

Microstructure and interlaminar shear property of carbon fiber-SiC nanowire/pyrolytic carbon composites with SiC nanowires growing at different positions

In order to improve the interlaminar shearing strength of carbon fiber/pyrolytic carbon (Cf/PyC) composites, SiC nanowires (SiCNWs) growing at different positions were introduced into carbon fiber/pyrolytic carbon composites to generate carbon fiber-SiC nanowire/pyrolytic carbon (Cf-SiCNWs/PyC) composites. Cf-SiCNWs/PyC composites were prepared by sol-gel and isothermal chemical vapor infiltration (ICVI) method. The morphology, microstructure and compositions of composites were investigated by SEM, TEM, XRD and XPS. The interlaminar shearing strength was tested and the effect of SiCNWs growth positions on the interlaminar shearing strength was investigated. The results showed that SiCNWs were consisted of perfect single crystalline structure of β-SiC with diameter of 160–200 nm. The SiCNWs could grow at four kinds of positions to combine with carbon fibers to form multi-scaled reinforcements (micro-scaled carbon fibers and nanoscaled SiCNWs). The interlaminar shear strength of Cf-SiCNWs/PyC composites were increased by 78% compared with Cf/PyC composites without SiCNWs. The improvement of interlaminar shear strength was attributed to bridging and pull-out of multi-scaled reinforcements composed of carbon fibers and SiCNWs as well as the enhancement of fiber/matrix interface bonding generated by SiCNWs growing at different positions.

Effect of graphene oxide addition on the interlaminar shear property of carbon fiber-reinforced epoxy composites

Carbon fiber-reinforced composites were manufactured by hot pressing stacked carbon fiber prepregs using graphene oxide (GO)-modified epoxy resin as the matrix. Tetrahydrofuran was used as the solvent to disperse GO in the epoxy resin. Results showed that a homogeneous GO-modified epoxy system could be obtained, which was stable for approximately 3 h, long enough to produce the prepreg. The incorporation of 0.10 wt% GO into the epoxy resin achieved the largest interlaminar shear strength (ILSS) of 96.14 MPa for laminates, 8.05% higher than that without GO. Also, the glass transition temperature of the composite was increased by approximately 5 °C. The improvement of ILSS could be attributed to the toughening of the epoxy resin and an improvement in the interfacial adhesion between carbon fibers and epoxy matrix.

Addition of a small amount of multiwalled carbon nanotubes and flaked graphene to epoxy resin

The paper presents an attempt to evaluate the technically important properties of epoxy resin modified alternatively with multi-walled carbon nanotubes and flaked graphene. It is a presentation of experimental results supported by extensive referring to the professional literature. The nano-components were added in the amount which was economically justified and provides hope for a significant improvement of some of the properties of pure resin. Flowability, glass wettability, curing process and gelation time and curing shrinkage of the resin were evaluated. After the resin was cured, inner and outer hardness, thermal conductivity, flexural strength and impact resistance were measured. Glass fibre-reinforced laminates were also prepared with use of the nano-modified resin. The mechanical properties, interlaminar shear strength and flexural strength of the laminates, were evaluated for them. The obtained results showed either no effect or only technically slight effect of the nano-modification on the evaluated properties. Noticeable improvement in interlaminar shear strength and impact resistance for laminates containing resin filled with graphene can predestine this kind of modification as a method of increasing the delamination resistance of laminates.

Improvement of interlaminar shear strength of 2.5D fabric laminated composites with short-cut web interlayer

Abstract In this study, the short-cut web interlayer and three-dimensional (3D) needle-punched technique were used to improve the interlaminar shear strength (ILSS) of 2.5D fabric laminated composites. The ILSS was measured by the short beam testing method, and the tensile and bending tests were carried out to investigate the in-plane mechanical properties. Observations on microstructure and crack propagation were carried out. The damage mechanisms of different 2.5D fabric laminated composites were analyzed. The results showed that the short-cut web interlayer and 3D needle-punched technique resulted in the improvement of ILSS, and they affected the tensile and bending properties of 2.5D fabric laminated composites.

Effect of post-curing on thermal and mechanical behavior of GFRP composites

Curing cycle has a strong impact on the thermal and mechanical behavior of thermosetting polymers. The extent of cross-linking which is a strong function of curing temperature and time is directly linked to the glass transition temperature (Tg) of the thermosetting polymer. This transition temperature speaks about the transformation of the polymer from glassy state to rubbery state, hence decides the applicability of the material at certain temperature with certain degree of safety and reliability. Hence assessment of Tg and its possible improvement is quite essential from material point of view. The present study is emphasized on the impact of post curing parameters on thermal as well as mechanical behavior of glass fiber reinforced polymer (GFRP) composite. Post curing was carried out at 3 different temperatures (80°C, 110°C and 140°C) for different time periods (2h, 4h, 6h, 8h and 12h). Short beam Shear (SBS) test was performed on each of the post cured samples to determine the apparent Interlaminar Shear Strength (ILSS) and the corresponding Tg was also evaluated using differential scanning calorimetry (DSC) analysis. The results revealed that the ILSS and Tg are significantly affected with post curing parameters. No significant change in ILSS was obtained at 80°C over the entire curing time. In case of 110°C a smooth increment in ILSS was observed with time (even till 12 hrs). For samples post cured at 140°C a rapid improvement in ILSS takes place with time followed by saturation. With all the possible combinations of curing temperature and time, optimum values are noticed at 140°C for 6 hrs.

The interlaminar shear strength and impact performance of polytetrafluoroethylene fiber-reinforced polymethyl methacrylate composites filled with silicon dioxide

The interlaminar shear strength (ILSS) of polytetrafluoroethylene (PTFE) fiber-reinforced polymethyl methacrylate (PMMA) composites enhanced by filled silicon dioxide (SiO2) is studied. The PMMA blends were prepared by combining the techniques of high-speed mechanical stirring. Experimental results showed that ILSS and impact properties of PMMA composites were improved. The largest improvement in ILSS and impact strength were obtained with 7 vol % loading of SiO2. ILSS and impact strength were improved by 15 and 50%, respectively, compared with the composite without SiO2. The fracture and surface morphologies of the composite specimens were characterized using scanning electron microscopy. This PTFE fiber-reinforced composite can be applied to bioengineering and fabrics.

Enhancing the adhesive wear performance of polyetherimide composites through nano-particle treatment of the carbon fabric

Rare earth compound Ytterbium fluoride (YbF3) in nano-size (40–80 nm) was employed for surface treatment of carbon fabric (CF) to improve its wettability with polyetherimide matrix. Composites were developed based on untreated and surface-treated CF with three doses, 0.1, 0.3, and 0.5 wt%, of YbF3 in ethyl alcohol suspension. The composites were analyzed for interlaminar shear strength (ILSS). Improvement in ILSS was observed for treated fabric reinforced composites and it was maximum (61%) for 0.3 wt% dose of YbF3. The adhesive wear performance of composites was evaluated by sliding a pin of composite against mild steel disc under varying loads (200–600 N). The treated fabric composites exhibited lower coefficient of friction (μ) and higher wear resistance (W R). ILSS and W R showed good linear correlation. Both properties were highest for 0.3% YbF3 dosing. Increased roughness of fiber surface and adhesion of nano-particles on the fiber surface was observed in scanning electron microscopic (SEM) studies. SEM studies of worn surfaces of composites were performed to understand wear mechanisms. Atomic force microscopic studies indicated substantial increase in roughness value of CF.