Browsing by Author "Karahan, Nevin"
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Item Ballistic impact behavior of the aramid and ultra-high molecular weight polyethylene composites(Sage Publications, 2015-01) Jabbar, Abdul; Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; AAK-4298-2021; 8649952500; 22034801200This paper presents the experimental study of fiber type, fabric structure, orientation of fabric plies and thickness on the ballistic impact behavior of aramid and ultra-high molecular weight polyethylene (UHMWPE) composite laminates. Aramid composite laminates are reinforced by three kinds of fabric structures and UHMWPE composite laminates are reinforced by two kinds of fabric structures. The laminates are fabricated via autoclave curing process. The ballistic behavior of composite laminates is evaluated by ballistic limit velocity, and energy absorbed at ballistic limit. Through a series of ballistic tests, it is demonstrated that unidirectional composite laminates exhibit higher ballistic limit velocity and energy absorption on unit weight basis compared to other laminates. Interesting results are shown by UD-UHMWPE-H62 (R) and UD-UHMWPE-Endumax (R) fabric-reinforced laminates. Orientation of fabric plies is found to have insignificant effect on ballistic behavior irrespective of material type. A bi-linear relationship is found between the ballistic limit velocity, energy absorption and specimen thickness.Item Blast performance of demining footwear: Numerical and experimental trials on frangible leg model and injury modeling(Amer Soc Testing Maretials, 2018-03) Karahan, Emir Ali; Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; AAK-4298-2021; 8649952500; 22034801200TBThis study reveals the protective efficacy of a personal protective boot against mine blasts, both experimentally and numerically. By employing analyses conducted with the use of different amounts of explosives, the protective efficacy of the developed boot is compared to a typical military boot as reference. Both for analysis and verification tests, a ballistic gelatin covered frangible leg model was used. Strain energy that is exerted on the leg was determined with numerical analyses and verified with data obtained from strain gauges that were placed on the leg model. By employing the dynamic finite-element method, the physical injury that occurred to the leg model was examined and compared with the results of the blast test. The Type 2 boot decreased the strain energy by approximately 80 % compared with the Type 1 boot. This observation was also verified with measurements obtained from strain-gauge sensors placed along the tibia. It was observed that the damage occurring on the tibia was limited to local injuries and concentrated at a single spot without causing any fractures with the Type 2 boot. As a result of axial load, the leg with the Type 1 boot demonstrated fractures at several points rather than a fracture at a single point based on deflection. Hence, the latter case yields irremediable injuries.Item Blast performance of demining footwear: Numerical and experimental trials on frangible leg model and injury modeling(Springer, 2018) Ahram, T.; Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; AAK-4298-2021; 8649952500; 22034801200This study reveals the protective efficacy of a personal protective boot against mine blasts both experimentally and numerically. By employing analyses conducted with the use of different amounts of explosives, the protective efficacy of the developed boot is compared to a typical military boot as reference. Both for analysis and verification tests, a ballistic gelatin covered frangible leg model was used. Strain energy that is exerted on the leg was determined with numerical analyses and verified with data obtained from strain gauges that were placed on the leg model. By employing the dynamic finite elements method, the physical injury that occurred to the leg model was examined and compared with the results of the blast test. The type-2 boot decreased the strain energy by approximately 80% compared with the type-1 boot. This observation was also verified with measurements obtained from strain gauge sensors placed along the tibia bone. It was observed that the damage occurring on the tibia bone was limited to local injuries and concentrated at a single spot without causing any fractures with the type-2 boot. As a result of axial load, the leg with the type-1 boot demonstrated fractures at several points rather than a fracture at a single point based on deflection. Hence, the latter case yields irremediable injuries.Item Development and characterization of hybrid green composites from textile waste(Springer, 2018) Masood, Zaid; Nawab, Yasir; Trzcielinski, S.; Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; AAK-4298-2021; 8649952500; 22034801200The current study focused on the use of textile industry waste (cotton and jute) and glass fabric for the development of hybrid composites. Composites were fabricated using either a single reinforcement or different fractions of cotton, jute and glass fabric. A good fibre-matrix interface was observed using Scanning Electronic Microscopy (SEM). The mechanical performance of the developed composites was analyzed under certain loads. The tensile and flexural properties of the composites developed from waste material was found lower as compared to the glass fiber composites, while hybrid composites had comparable properties. Regression equations were also developed to predict the mechanical properties of the hybrid composites. The results revealed that, after some pre-treatment (mercerization and desizing) textile waste materials can be used with virgin material in reinforcement part of composite to decrease the cost but with optimum mechanical properties. This usage of textile waste will be helpful for its value addition and solving the waste disposal problems.Item Development of an innovative sandwich composites for the protection of lower limbs against landmine explosions(Sage Publications, 2016-12) Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; AAK-4298-2021; 8649952500; 22034801200This article includes the results of blast tests that were performed with the aim of comparing the energy absorption and protection efficiencies of protective boots with different sole configurations. The tests were performed using a frangible leg model vestured with protective boots. Strain values were measured during the blast tests to determine the protection efficiencies of different sole configurations of the protective boots. Filling honeycomb cells with glass microspheres dramatically increased the energy absorption. In the type-3 samples, which were produced with these microspheres, the strain through the tibia axis decreased 83-47% for different explosive weights compared with the type-1 samples and 52-13% for different explosive weights compared with the type-2 samples; the type-1 and type-2 samples do not have glass microspheres. Bone damage and mine trauma score values show that the type-3 boot provides absolute protection against 40g of Trinitrotoluene (TNT) and that the injuries that occurred in the tests performed using 70 and 110g of TNT can be reduced to a curable level without amputation.Publication Effect of structural hybridization on ballistic performance of aramid fabrics(Sage Publications, 2019-06-01) Karahan, Mehmet; Karahan, Nevin; Nasir, Muhammad Ali; Nawab, Yasir; KARAHAN, MEHMET ALİ; KARAHAN, NEVİN; Bursa Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu; FEC-4798-2022; AAK-4298-2021This article presents an investigation regarding the ballistic performance of hybrid panels formed by combining woven and unidirectional (UD) para-aramid fabrics. For this purpose, hybrid panels are formed by combining woven and UD para-aramid fabrics with different ply ratios. The hybrid panels formed in this way are subjected to ballistic tests according to National Institute of Justice (NIJ) standard. The results show that hybrid panels present 4.48% less trauma depth as compared to 100% woven fabric panels and 3% less trauma diameter as compared to 100% UD fabric panels. Furthermore, 13.9% less energy is transmitted to the back side of hybrid panels as compared to 100% UD fabric panels. The energy absorbed per unit weight in hybrid panels is 8.48% more as compared to 100% woven fabrics. Additionally, in wet conditions, less trauma depth of hybrid panels is observed as compared to both 100% woven and 100% K-Flex UD fabric panels. No significant difference is realized in trauma diameter between hybrid panels and 100% woven fabric panels in wet conditions. However, 3.25% less trauma diameter is noticed in hybrid panels as compared to 100% UD fabric panels.Item Effect of weaving structure and hybridization on the low-velocity impact behavior of woven carbon-epoxy composites(Inst Chemical Fibres, 2014) Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu/Tekstil, Giyim, Ayakkabı ve Deri Bölümü.; AAK-4298-2021; 8649952500; 22034801200In the current study the low-velocity impact behaviour of composite materials obtained from carbon and carbon-aramid hybrid woven fabrics of different constructions, produced from the same yarn and under the same production conditions, was determined, and the effects of the weaving structure and hybridisation on the low velocity impact properties were investigated. Depending on the weaving structure, the best results were obtained for twill woven composites. The energy absorption capacity was increased by around 9 - 10% with hybridisation. It was observed that peak load values varied with a coefficient between 0.84-0.97 for hybrid composites, whereas the range was 0.49 - 0.87 for 100% carbon composites, depending on the bending stiffitess.Item Evaluation of foot protection effectiveness against AP mine blasts: Effect of deflector geometry(Amer Soc Testing Maretials, 2017) Kamberoǧlu, Murat; Alpdoğan, Can; Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; AAK-4298-2021; 8649952500; 22034801200In this study, the effectiveness of blast deflectors used in protective footwear against antipersonnel (AP) mines was investigated. The tip angle of a V-shaped deflector and the overall shape (symmetrical, unsymmetrical) were chosen as the design parameters to be examined, whereas parameters such as deflector material and wall thickness were kept constant. Both explicit dynamic finite element analysis (LS-Dyna) and blast tests were performed to evaluate the effectiveness of these design parameters. The analysis results were also verified with the blast tests. A visual (qualitative) comparison between the analysis results and the blast tests showed a good agreement on the final deformed geometry of the deflector, which suggested that the simulation was able to capture the energy absorption mechanism of the deflector. The analysis results showed that the peak force transmitted to the leg decreased tremendously with the addition of blast deflectors. When compared to the case with no deflectors, an unsymmetrical and symmetrical deflector reduced the peak force by a factor of 24 and 36, respectively.Publication Geometrical analysis of 3d integrated woven fabric reinforced core sandwich composites(Inst Chemical Fibres, 2019-01-01) Jabbar, Abdul; Zubair, Muhammad; Karahan, Mehmet; KARAHAN, MEHMET; Karahan, Nevin; KARAHAN, NEVİN; Bursa Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; 0000-0001-6900-4147; 0000-0003-3915-5598; 0000-0003-2362-517X; JQW-3721-2023; AAK-4298-2021; JON-7556-2023; O-2447-2015The variability of the internal geometry parameters, such as the waviness of yarns, cross sections of yarns and local fibre volume fraction of 3-dimensional (3D) integrated woven core sandwich composites affects their mechanical properties. The objective of this study was to define the geometrical and structural parameters of 3D integrated woven core sandwich composites, including the fold ratio of pile threads, the fabric areal weight and the fib re volume fraction by changing the core thickness of 3D sandwich core fabric. 3D fabrics with different core thicknesses were used for reinforcement. It was confirmed that the pile fold ratio, slope angle and pile length increase with an increase in the core thickness of the fabric. The difference between the calculated and experimental areal weights of fabrics was in the range of 5-13%. A novel approach was also presented to define the fibre volume fraction of 3D woven core sandwich composites.Item Influence of stitching parameters on tensile strength of aramid/vinyl ester composites(Kaunas University of Technology, 2013-03-19) Karahan, Mehmet; Ulcay, Yusuf; Karahan, Nevin; Kuş, Abdil; Uludağ Üniversitesi/Teknik Meslek Yüksekokulu/Tekstil Bölümü.; Uludağ Üniversitesi/Mühendislik Fakültesi/Tekstil Mühendisliği Bölümü.; Uludağ Üniversitesi/Teknik Meslek Yüksekokulu/Makine Bölümü.; AAK-4298-2021; AAG-9412-2021; 8649952500; 6601918936; 22034801200; 57196667786Stitching process is used to provide structural integrity and through-the-thickness reinforcement in the composite materials. In this study, the effect of sewing parameters on tensile strength in stitched composite laminates was examined. In the production of composite laminates, Twaron T-750 type plain weave fabric was used as reinforcement material and a Polives 702 Bisphenol-A type epoxy based vinyl ester as resin. The effects of stitch density and stitch direction or stitch pattern on tensile strength of composite samples were studied and, as a result of the experiments, it was observed that higher tensile strength occurs with low stitch densities in stitched laminates.Item Influence of weaving structure and hybridization on the tensile properties of woven carbon-epoxy composites(Sage Publications, 2014) Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; AAK-4298-2021; 8649952500; 22034801200In this study, the mechanical properties of composite materials obtained from carbon and carbon-aramid hybrid woven fabrics produced in different constructions with the same yarn and under the same production conditions were determined, and the effects of weaving structure and hybridization on the mechanical properties were investigated. For this purpose, the geometric properties of carbon fabrics made from 12K carbon yarn with four different weaving structures and two carbon-aramid hybrid fabrics made of 12K carbon yarn and aramid yarn with two different structures were defined, and the mechanical properties of the composite materials were investigated under uniaxial tensile loading. The mechanical properties of the composite materials produced from the carbon and carbon-aramid hybrid fabrics were compared. The effects of weaving structure and hybridization on the mechanical properties were determined. Based on the weaving construction, Young's modulus and the tensile strength declined approximately 34-39% and 24-27%, respectively. However, Young's modulus was 16-63% higher than the expected value for the hybrid composites.Item Investigation into the tensile properties of stitched and unstitched woven aramid/vinyl ester composites(Sage Publications, 2010-06) Karahan, Mehmet; Ulcay, Yusuf; Eren, Recep; Karahan, Nevin; Kaynak, Gökay; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; AAK-4298-2021; 8649952500; 6601918936; 55999849700; 22034801200; 12042075600In this study, the influence of stitch bonding on the tensile strength and tensile modulus in plain woven Twaron T-750/vinyl ester composites in the direction of thickness was examined. The effect of stitch density was investigated in longitudinal (warp) and transverse (weft) directions as a parameter. The space (opening) geometry and the deformation caused by the stitching process around stitch points were investigated. The stitching tension, stitch thread type and diameter were kept constant throughout the study. An increase in the tensile strength was observed for low stitching densities while there was no change in the tensile strength for medium stitching densities. A decrease in the tensile strength was observed for high stitching densities. It is especially noted that the tensile strength, which is on the transversal direction perpendicular to stitch direction, decreased with stitching density and tensile deformations initiated much earlier in this direction. It was understood that fiber deviations and resin rich areas were much more effective on these decreases compared with fiber deformation.Item Investigation of the properties of natural fibre woven fabrics as a reinforcement materials for green composites(Inst Chemical Fibres, 2016) Özkan, Fatma; Yıldırım, Kenan; Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; AAK-4298-2021; 8649952500; 22034801200The mechanical properties of flax and jute woven fabrics were investigated and compared with each other. Mechanical properties of the yarns and fabrics were characterised and compared for each scale. The fabric structure, yarn physical properties, fibre cross-section, and fibre molecular structure parameters of the fabric were investigated. FTIR and TGA thermogram analyses were applied to the fabrics to characterise them. The fabric tensile strength was attributed to the composite tensile strength, but there was not a direct relation. The tensile strength of natural fibre fabrics was determined as significantly reduced depending on the temperature increase. This condition should be considered as an important limitation for composite applications.Item Investigation of the tensile properties of natural and natural/synthetic hybrid fiber woven fabric composites(Sage Publications, 2015-05) Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksek Okulu/Tekstil, Giyim, Ayakkabı ve Deri, Tekstil Teknolojisi.; 0000-0003-3915-5598; 0000-0001-6158-2997; AAK-4298-2021; 8649952500; 22034801200The development of polymer composites containing natural fibers as a sustainable alternative material for certain engineering applications, particularly aerospace and automotive applications, is a popular area of research. In this study, the mechanical properties of flax, jute and jute/carbon woven fabric composites were investigated and compared with those of 3K carbon woven fabric composites. The results of this study demonstrate the utility of natural fibers in composite applications. Furthermore, it is observed that the mechanical properties of natural fibres are significantly affected by changes in temperature. Experimental results prove that the mechanical properties of natural fiber composites are significantly lower than those of carbon fiber composites, but the hybridization of carbon and jute fibers can result in a composite material with enhanced mechanical properties.Item Low velocity impact characteristics of 3D integrated core sandwich composites(Sage Publications, 2012-06) Ivens, Jan; Karahan, Mehmet; Gül, Hakan; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; 0000-0003-3775-3500; AAK-4298-2021; AAK-4563-2021; 8649952500; 55165493000; 22034801200In this paper, the low velocity impact characteristics and impact damage of sandwich composites, produced at four different core thicknesses from 3-dimensional (3D) integrated sandwich fabrics, with and without foam filling, have been examined. The 3D sandwich fabrics have been produced using the same yarn and weaving densities. Thus, the impact characteristics are only affected by the core thickness and whether foam filling is used or not. Low velocity impact tests have been conducted at 32 and 48 J energy levels. The impact behavior has been determined as a function of the peak load, the energy to peak load, the time to peak load and the absorbed energy. The impact damage and the change in the compressive strength after impact have been analyzed. The findings obtained indicate that core-skin delamination on 3D sandwich composites has been fully prevented. Impact tests carried out on integrated 3D sandwich structures have shown that impact damage is limited to the vicinity of the point of impact and does not affect the integrity of the structure. This indicates that such damage can be easily repaired and the service life of the product can be sustained.Item Quasi-static behavior of three-dimensional integrated core sandwich composites under compression loading(Sage Publications, 2013-03) Ivens, Jan; Karahan, Mehmet; Karahan, Nevin; Gül, Hakan; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; 0000-0003-3775-3500; AAK-4563-2021; AAK-4298-2021; 55165493000; 22034801200; 8649952500In the current study, the effect of the thickness and the foam density in three-dimensional integrated woven sandwich composites on quasi-static properties was investigated. For this purpose, produced samples were subjected to uniaxial flatwise compression tests and their compression strength and moduli were determined. Obtained results were optimized by taking core thickness, foam density and panel weights into consideration. Damages that occurred on the tested samples were reported. When compared to conventional foam core sandwich composites, it was found that three-dimensional integrated sandwich composites have better compression properties and due to the fact that the pile yarns in the core and the foam support each other.Item The solar properties of fabrics produced using different weft yarns(Sage Puplications Ltd, 2018) Yıldırım, Kenan; Kanber, Asuman; Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; AAK-4298-2021; FEC-4798-2022; 8649952500; 22034801200Woven fabric is composed of two yarns system, known as the weft and warp yarns. Each yarn system has an effect on the physical, performance, and optical properties of fabric. Any change in one or both yarn systems greatly alters the fabric properties. The solar and luminous properties of fabrics are also affected by altering the weft yarn or both yarn systems. This study investigates the effect of altering the weft yarn system on the solar and luminous properties of fabrics. The differences in the weft yarn in the fabrics were based on the weft yarn structure, including the yarn linear density, amount of twist on the yarn, yarn evenness, hairiness, spinning method, fiber composition of the yarn, and weft density of the fabric. The fabric luminous and solar properties were measured according to EN 14500 using an ultraviolet-visible-near-infrared (UV/VIS/NIR) test device and calculated from the EN 410 standard test method. According to a variance analysis, the weft density factor is shown to have an effect on the solar properties of the fabric, especially the UV transmittance properties of the fabric. Although non-parametric test results with a 95% confidence level show that the yarn structure does not influence the solar characteristics of the fabric, we show from the test results that the yarn structure influences the solar properties of the fabric. Yarn hairiness was the dominant factor for the IR and visible portions of the solar radiation spectra. In the UV region, the fiber composition factor was found to be important. The effect of the yarn linear density was similar to the effect of the weft density factor. The solar transmittance decreases and the reflectance increases when the number of weft yarns per unit length is increased and the yarn linear density in the Ne numbered system is decreased. Increasing the yarn hairiness decreases the transmittance in the IR portion of the solar spectra. The degree of influence that the yarn structure has on the solar properties (with the exception of the UV portion) of the fabric was dominated by the number of weft yarns per unit length. The transmittance properties of the fabric were more affected by altering the yarn structure than the reflectance and absorbance properties.Item Static and dynamic mechanical properties of cotton/epoxy green composites(Inst Chemical Fibres, 2016) Koyuncu, Menderes; Shaker, Khubab; Nawab, Yasir; Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; 0000-0003-0379-7492; AAG-8536-2021; AAK-4298-2021; 8649952500; 22034801200A study on the effect of alkaline treatment on the mechanical properties of cotton fabric reinforced epoxy composites is presented in this paper. One hour treatment of cotton fabric was performed using three different concentrations of sodium hydroxide (NaOH) solution. 1% NaOH treated fabric reinforced composites exhibited maximum improvement in tensile strength. It was concluded that the said NaOH concentration improves interfacial adhesion between the cotton fabric and epoxy resin. Moreover the morphology of the fracture surface, evaluated by scanning electron microscopy (SEM), indicated that surface treatment can yield better adhesion between the fabric and matrix, demonstrating the effectiveness of the treatment. The dynamic mechanical analysis (DMA) results revealed that alkali treated (1% and 3% NaOH) fabric composites exhibit higher storage moduli and glass transition temperature (Tg) values as compared to the untreated fabric composites. However, for all the composite specimens, the storage modulus decreased with increasing temperature (25 -100 degrees C). Tg values of 50.9, 56.7, 52.8 and 37.7 degrees C were recorded for the untreated and (1%, 3% and 5%) treated composites, respectively. The tan delta values decreased for all the composites with increasing temperature, indicating enhanced interactions between the polymer matrix and fabric reinforcement.Item Static behavior of three-dimensional integrated core sandwich composites subjected to three-point bending(Sage Publications, 2013-05) Ivens, Jan; Karahan, Mehmet; Gül, Hakan; Karahan, Nevin; Uludağ Üniversitesi/Teknik Bilimler Meslek Yüksekokulu.; 0000-0003-3775-3500; AAK-4563-2021; AAK-4298-2021; I-4339-2016; 8649952500; 55165493000; 22034801200In the current study, the effect of the thickness and the foam density in three-dimensional integrated woven sandwich composites on quasi-static mechanical properties under three-point bending was investigated. Bending modulus and core shear modulus were determined by subjecting the samples, which were cut with varying span lengths according to their core thicknesses, to three-point bending test. Obtained results were optimized by taking core thickness, foam density and panel weights into consideration. Damages that occurred on the tested samples were reported. When compared to conventional foam core sandwich composites, it was found that three-dimensional integrated sandwich composites have superior mechanical properties and due to the fact that the pile yarns in the core and the foam support each other, contrary to conventional sandwich composites no catastrophic core breakage occurs under load, thus the load bearing capacity of the structure is sustained.Item Study of dynamic compressive behaviour of aramid and ultrahigh molecular weight polyethylene composites using Split Hopkinson Pressure Bar(Sage Puplications, 2017-01) Shaker, Khubab; Jabbar, Abdul; Nawab, Yasir; Karahan, Mehmet; Karahan, Nevin; Uludağ Üniversitesi/Meslek Yüksekokulu/Teknik Bilimler Yüksekokulu.; AAK-4298-2021; 8649952500; 22034801200In this paper, high strain rate compression properties of aramid and ultrahigh molecular weight polyethylene composites in the out-of-plane direction are tested at room temperature on a Split Hopkinson Pressure Bar apparatus. Tests were conducted on composites reinforced with woven or Uni-Directional (UD) fabrics made from aramid or ultrahigh molecular weight polyethylene as well as on composites reinforced with hybrid reinforcement. The strain rate is varied in the tests by changing the projectile shooting pressure. Four different pressures 2, 4, 6 and 8 bar were selected to change the strain rate. Stress-strain and energy absorption behaviour of eight type of samples were noted. Hybrid samples showed better performance in the energy absorption compared with other samples.