Browsing by Author "Soykok I.F."
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Item Effects of axial impacts at different temperatures on failure response of adhesively bonded woven fabric glass fiber/epoxy composite joints(SAGE Publications Ltd, 2015) Sayman O.; Soykok I.F.; Dogan T.; Dogan A.; Arikan V.Evaluating post-impact failure responses of single-lap adhesively bonded composite-to-composite joints in uniaxial static tensile loading was the main objective of the current experimental study. At first, axial tensile impacts having various energy levels (10, 15, 20, and 25 J) were applied to the joints at different temperatures (-20, 0, room temperature, 50, and 80). Afterward, the samples were secondarily subjected to static tensile loading at ambient temperature, so that reductions in joint strengths arising from the impacts performed under different loading conditions could be assessed. Consequently, it was definitely proved that each of the axial impacts performed in any loading case has a noticeable effect on ultimate joint strengths, proportionally to the acting condition. Besides, the combination of high energy and temperature sometimes appeared to be the reason of impact failure, which occurs instantly without being able to perform axial static tests. When applied energy and/or absolute difference from room temperature is increased, lower joint resistances could be measured during secondary tensile tests. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.Item End geometry and pin-hole effects on axially loaded adhesively bonded composite joints(Elsevier Ltd, 2015) Soykok I.F.Abstract An experimental investigation was performed to analyze the potential impacts of varying joint region geometries and adhesive filled pin holes on adhesively bonded composite structures. Tapers, especially half-length ones are observed to provide an anticipated progress in single lap joints. Besides, scarf joints with aligned adherends in the same plane exhibited enhanced stiffness and strength in consideration of single lap joints. In terms of the stiffness and strength, thickening of adherends was also found to be impressively efficient on composite single lap joints as well as scarf joints. Contrary to the expectation of that the hardened adhesive previously filled into the holes during adhesion would create a pin effect in load bearing, holey specimens exhibited poor performance and induced degradation in joint quality. © 2015 Elsevier Ltd. All rights reserved.Item Strength comparison of ductile and brittle adhesives under single and repeated impacts(Springer International Publishing, 2015) Kemiklioglu U.; Sayman O.; Batar T.; Soykok I.F.; Akderya T.; Akan E.In this study, the failure strengths of adhesively bonded joints were investigated. The glass fiber epoxy composites used as adherends were manufactured by using vacuum assisted resin infusion method (VARIM). The adhesively joint materials were Loctite-9466 and DP-460 as a brittle and ductile material, respectively. Since the strengths of these materials are close to each other under static loading, the applied axial energies were determined using different levels of 5, 10, 15 and 20 Joules. In order to determine the energy characteristics of the experiments, axial impact loadings were applied as both single and repeated three times under the same conditions. The results showed that the failure strengths of these two different adhesives of Loctite-9466 and DP460 changed depending on single and three times repeated axial impact loadings. This paper is intended to give an overview between ductile and brittle adhesives under both single and repeated impacts. In addition, it will help for designers who need information on mechanical properties of ductile and brittle adhesives under single and repeated impacts. © 2015, Kemiklioglu et al. All Right Reserved.Item The mechanical behaviour of adhesively bonded composite joints under repeated axial impacts at different temperatures(Walter de Gruyter GmbH, 2017) Kemiklioglu U.; Sayman O.; Soykok I.F.; Akderya T.; Dere R.In this study, the failure strength of single-lap adhesively bonded joints was investigated. The glass fibre epoxy composites used as adherends were manufactured by using a vacuum-assisted resin infusion method. These composites were bonded with a commercial material of epoxy-adhesive DP-460, which can be cured easily at room temperature. The specimens were built by bonding, and then repeated axial impact loads having various energy levels (0, 5, 10, 15, and 20 J) were implemented to the single-lap adhesively bonded composite joints at different temperatures (-20°C, 0°C, 20°C, 40°C, and 60°C). Subsequently, the specimens were exposed to static tensile loading at the same temperatures as those applied during the primary impacts. The variation in failure loads due to the effects of repeated axial impact loadings at different temperatures were investigated. Generally, the increase of impact energy level from 0 to 20 J leads to a gradual decrease in failure loads at all temperature levels except for the specific value of 40°C. © 2017 Walter de Gruyter GmbH, Berlin/Boston.Item Degradation of single lap adhesively bonded composite joints due to hot water ageing(Taylor and Francis Inc., 2017) Soykok I.F.Joints, which are the most critical part of fibre-reinforced epoxy plastic structures, can be exposed to continuous hydrothermal action. In order to estimate their long-term performance, an accelerated ageing process was performed on adhesively bonded joints of glass-fibre-reinforced epoxy plastics with [0/90/45/−45]s fibre orientations. Changes in the static tensile properties of single lap shear samples due to hot-wet exposure were investigated for one- and two-week immersion periods and at three different water temperatures (50°C, 70°C, and 90°C). Both the ageing temperature and immersion time were found to be influential on load–displacement characteristics, maximum failure loads, and apparent failure modes of joints bonded with Loctite Hysol-9466 epoxy type adhesive. Due to the hydrothermal exposure, maximum failure loads, distance to failure values, and stiffness of joints decreased by a certain amount in proportion to the immersion time and temperature. While unaged samples and those aged at 50°C and 70°C exhibited mainly light fibre-tear (LFT) failures, the samples treated at 90°C ruptured through the material cross section in stock-break (SB) failure mode. © 2017 Taylor & Francis.Item Effects of carbon nanotube inclusion into the carbon fiber reinforced laminated composites on flexural stiffness: A numerical and theoretical study(Elsevier Ltd, 2019) Taş H.; Soykok I.F.Because of increased usage areas, and advances in characterization of the nanostructured materials, determination of the engineering properties of composites that includes carbon nanotubes has gained importance. It is possible to designate material properties of carbon nanotube based composites theoretically and experimentally. In this study, engineering constants of carbon nanotube based unidirectional carbon fiber reinforced composite lamina determined theoretically with two different approaches. Then, a composite plate whose laminas were stacked up as a [0°/+45°/-45°/90°]s layup was built up in ANSYS, ACP Module. Finally, three point bending analyzes were performed separately under concentrated and distributed load. The results showed that there were negligible differences between the engineering constants obtained from two different theoretical approaches. Engineering constants, E1, E2, G12 and G23, increased as the added carbon nanotube fraction is increased. Besides that, flexural rigidity of composite plate also showed ever-decreasingly increase, as carbon nanotube content is increased. The results of theoretical and numerical bending analyzes exhibited a good agreement with the maximum percentage relative error of 9.1. © 2018 Elsevier LtdItem Evaluation of the failure responses of filament wound and pre-preg wrapped glass fiber/epoxy composite tubes under quasi-static torsional loading(Institute of Physics Publishing, 2019) Soykok I.F.; Ozcan A.R.; Tas H.This paper introduces an experimental and numerical investigation into hollow cylindrical thin-walled glass fibre reinforced epoxy matrix composite shafts produced by using both pre-preg wrapping and filament winding methods. The filament wound samples were manufactured with four different helix angles ([±30]FW, [±45]FW, [±60]FW, and [±75]FW ), whereas [0, 90]PP pre-pregs was utilised for producing the wrapped kind of samples. In order to assess the quasi-static failure responses, the samples were subjected to increasing amount of torsional load at a fixed angular rotation speed. The experimental findings of [±30]FW, [±45]FW, and [±60]FW samples were found to be very compatible with those obtained via Finite Element Analysis (FEA). Contrarily, the numerical model were not able to describe accurately the load - displacement behaviour of [±75]FW and [0, 90]PP with the exception of the initial loading phase. [±45]FW was found as the most favourable option for designers in terms of torsional stiffness. Whereas, those characterised by [±30]FW, and [±60]FW exhibited very close torsional resistances in a difference range of only 5%. [0, 90]PP exhibited the lowest average torsional failure resistant and stiffness but the highest average rotation angle before rupture. © 2019 IOP Publishing Ltd.Item Puncture resistance of STF impregnated MWCNTs-grafted carbon fabrics(Elsevier Ltd, 2021) Taş H.; Soykok I.F.In this study, STF with the silica concentration of 20 wt% was fabricated. Functionalized multi-walled carbon nanotubes (MWCNTs) were chemically bonded onto the carbon fibers by using grafting technique. In grafting technique, DMF/PAN fiber/MWCNTs suspension sprayed onto each surface of carbon fabric and MWCNTs were grafted by a thermal treatment at 250 °C. Neat and MWCNTs-Grafted carbon fabrics were impregnated with STF with the silica loading of 20 wt%. Then, dynamic and quasi-static puncture resistance of neat, STF impregnated, MWCNTs-Grafted and MWCNTs-Grafted-STF impregnated carbon fabrics were examined. STF impregnation was detected to lead to a decrease in dynamic puncture resistance and an increase in quasi-static puncture resistance. Dynamic puncture resistance of MWCNTs-Grafted carbon fabric was found to be less than neat fabrics due to larger gaps between yarns occurred after thermal stabilization. Also, due to the greater gap between yarns, complete perforation occurred at lower penetration depth in MWCNTs-Grafted carbon fabrics than neat carbon fabrics in quasi-static puncture tests. © 2021 Elsevier LtdItem Effect of drop weight impact on the torsional-loading behavior of filament wound and prepreg-wrapped composite tubes(SAGE Publications Ltd, 2021) Soykok I.F.; Tas H.; Ozdemir O.; Kandas H.This article presents an experimental study on the torsional behavior of composite tubes subjected to impact loadings. Four types of composite tubes with the winding angle of 30°, 45°, 60°, and 75° ([±30]FW, [±45]FW, [±60]FW, and [±75]FW) were produced with the filament winding method. Besides, a [0,90]PP composite tube was manufactured with the prepreg wrapping technique. After the composite tubes were impacted at 2.5 J, 5.0 J, and 7.5 J, non-impacted and impacted composite tubes were tested under torsional loading. Contact force–deformation curves of impacted tubes are presented. Torsional moment–twist angle relations for both impacted and non-impacted composite tubes were obtained. In addition, front view and side view of the impacted zone of composite tubes are given. The results showed that sample [±60]FW had the best impact performance with regard to absorbed energy. The impacted samples of [±60]FW and [±75]FW had the lowest torsional strength for each energy level. © The Author(s) 2020.Item Investigation of the Low Velocity Impact Behaviour of Shear Thickening Fluid Impregnated Kevlar, Hybrid (Kevlar/Carbon) and Carbon Fabrics(Korean Fiber Society, 2021) Taş H.; Soykok I.F.In this study, unlike the previous studies focusing merely on high-performance fabrics (i.e, aramid based Twaron, Kevlar) low velocity impact behaviour of neat and shear thickening fluid (STF) impregnated kevlar, hybrid (Kevlar/Carbon) and carbon fabrics was investigated. In the first stage, STFs with the silica concentrations of 5 wt%, 10 wt%, 15 wt% and 20 wt% were produced separately and the rheological measurement of each individual fluid concentration were carried out. In the second stage of the study, kevlar, hybrid and carbon fabrics were impregnated by STF having a silica content of 20 wt%. Yarn pull-out tests, dynamic puncture tests and quasi-static (QS) puncture tests were carried out on both the neat and impregnated fabrics. The rheological measurements showed that, the resulting silica/PEG400 suspensions exhibit good shear thickening behaviours, however it is not the case for those under a critical silica concentration. The yarn pull out tests revealed that, STF enhances the inter-yarn frictions of all three types of fabric. Correspondingly, STF positively affected the dynamic puncture resistance of kevlar and hybrid fabrics, while it had an adverse effect on carbon fabric. Besides, STF caused increases on the QS puncture resistances of all three fabric types. © 2021, The Korean Fiber Society for Fibers and Polymers and Springer.Item Determinating optimum combination of ageing and manufacturing parameters for laminated composites using response surface methodology(SAGE Publications Ltd, 2023) Öztürk R.; Taş H.; Soykok I.F.This study mainly focuses on the effects of ageing and manufacturing parameters on the water absorption behaviour and mechanical characteristics of the glass-fibre reinforced polymer (GFRP) composites, and multiple optimizations of these parameters based on the quasi-static mechanical properties and low-velocity impact performances. Utilizing response surface methodology (RSM), an experimental design was executed varying curing temperature (20-100°C), ageing temperature (20-70°C) and salinity (3-35%). After 59-days ageing period, gravimetric, tensile and low-velocity impact tests were conducted to assess weight gain at saturation, changes in tensile strength, elasticity modulus, peak force and peak energy. Tensile fracture surfaces of aged and un-aged samples were examined using scanning electron microscopy. ANOVA results indicated the adequacy of RSM models, supported by high R2 (>80%) and R2adj (>65%) and proper residual distribution. Gravimetric tests revealed that higher curing and ageing temperatures resulted in greater water sorption-induced weight gain, while elevated salinity had the opposite effect. Ageing temperature and salinity are the most influential factors on tensile strength change. Optimal mechanical properties, minimizing differences between aged and un-aged samples, were achieved at 100°C curing temperature, 20°C ageing temperature and 19.8% salinity. Data from this study can be a valuable reference for designing GFRP composites, particularly in marine applications. © The Author(s) 2023.Item Effects of natural mica particle fillers on the mechanical properties of glass fiber/epoxy composite plates(Springer Science and Business Media Deutschland GmbH, 2024) Soykok I.F.; Taş H.Due to its high tensile and bending strength as well as high modulus (172 GN/m2), mica is a promising additive to improve the performance of polymer composites. Additionally, since it is abundant in nature and therefore cost-effective, it can be an alternative to commonly used but costly particles like carbon nanotube, graphene, and silica. This study focused on the effect of mica particles on the mechanical characteristics of glass fiber-reinforced laminated composites. Unlike the conventional production methods, a layer-wise method was adopted in order to add micro-mica particles into the glass fiber/epoxy composite. Composite plates with 1-, 3-, and 5-layer mica treatment as well as untreated composite plates were manufactured. Mechanical characteristics determined by tensile, three-point bending, and low-velocity impact tests were examined as a function of micaceous layer number. The interior structure of the composites was scanned by the use of scanning electron microscopy. According to the tensile and three-point bending tests, the micro-mica particle fillers failed to display the anticipated positive effect on strength values. Nevertheless, remarkable increases were observed in the average flexural modulus of mica-filled samples in comparison to the control samples without mica content. Also, the average peak energies during low-velocity impact tests were increased by the effect of mica fillers such that the average peak energies for the 1-layer, 3-layer, and 5-layer samples increased by 12.9, 1.9, and 10.3%, respectively, in comparison to the control samples. © 2023, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.Item Investigating fabric interlayer effects on tensile loading limits of adhesively bonded single-lap composite joints(SAGE Publications Ltd, 2024) Taş H.; Soykok I.F.This paper investigates enhancing the effectiveness of glass fiber/epoxy composite single-lap bonded joints by using fabric interlayers between the adherends. It was aimed to evaluate the changes in the joint tensile strength depending on the parameters such as different interlayer fabric types (S2-glass fabric and Kevlar fabric), numbers of interlayers (0, 1, 2, and 3), clamping pressure (0, 4, and 6 MPa), and temperature (20, 55, and 80°C) applied to the joint region throughout the curing period. Significant enhancements in peak tensile forces were observed by varying these parameters. The most substantial increase in tensile properties was achieved for the joint with two-layer S2 fabric fabricated at 4 MPa pressure and 55°C curing temperature, denoted as “2L-S2-P4-T55.” Compared to a non-layered joint, those with 1, 2, and 3 S2 fabric interlayers exhibited 35.5%, 39.6%, and 45.2% increases in tensile peak force, respectively. Increasing bonding pressure from 0 MPa to 4 MPa resulted in a 5.2% tensile failure load increase for double S2 fabric interlayered joints cured at 20°C, but a 6.7% decrease at 6 MPa. Using one-layer Kevlar fabric instead of one-layer S2 fabric caused a 15.2% drop in tensile peak force, still 14.9% higher than the non-layered joint. © The Author(s) 2024.