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Öğe Behavior of CFRP-strengthened RC beams with circular web openings in shear zones: Numerical study(Elsevier Science Inc, 2022) Ozkilic, Yasin Onuralp; Aksoylu, Ceyhun; Yazman, Sakir; Gemi, Lokman; Arslan, Musa HakanIn practice, especially the basement floor beams are drilled and damaged by the users. In some cases, this damage to the beams can be significant for the load-bearing element and the whole structure. In this study, the behavior of reinforced concrete beams with circular openings and the failure types resulting from strengthening these beams with CFRP are parametrically investigated. The diameter of the opening/beam height ratio (D/H), con-crete compressive strength, stirrup spacing, the position of the opening to the beam support, the type of CFRP application, CFRP ply orientation, and the number of CFRP layers were selected as parameters. Numerical models were verified using 9 specimens having different circular openings with/without CFRP strengthening and the analyses of 95 numerical models with the selected parameters were carried out utilizing the finite element program, ABAQUS. The ultimate load capacity, ductility, stiffness, energy dissipation capacity and failure modes of the beams were determined. As a result of the study, it was observed that there was no significant loss in ductility for the beams with D/H < 0.3 and the number of CFRP layer and type of application did not have a significant effect on D/H < 0.44. However, for the beams with D/H > 0.64, the CFRP application that completely surrounds openings should be preferred instead of partial CFRP strengthening. In addition, the concrete strength is an effective parameter for the beams with D/H < 0.44. The effect of the stirrup spacings in the beam on the ductile behavior was also limited with the increase in the hole diameter. The number of CFRP layers should theoretically be 4 for an effective strengthening in beams with D/H > 0.44. Finally, U wrapping is recommended instead of using full wrapping. It has been seen that the location and diameter of the hole are very important parameters in the failure type of the beam.Öğe A Comparative Study on the Effect of CNT or Alumina Nanoparticles on the Tensile Properties of Epoxy Nanocomposites(Springer Heidelberg, 2019) Yazman, Sakir; Samanci, AhmetIn this paper, the mechanical properties of the carbon nanotube (CNT) or alumina (Al2O3) nanoparticles (NPs)-modified epoxy composites were investigated experimentally. Composite dog-bone tensile specimens were prepared and tested according to ASTM D638-14 standards with CNT or Al2O3 nanoparticle contents of neat, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75 and 2.0% of the total resin weight. In order to compare the effect of nanoparticle type and content on the mechanical properties, tensile stress-strain curves were drawn for each parameter. Also, the ultimate tensile strength (UTS), Young's modulus and toughness values were obtained and compared. Considerable improvements of the mechanical properties were observed by adding NPs. The results indicated that the UTS, Young's modulus, and toughness values reached a maximum with an increment of 27.6, 18.7 and 187.9%, respectively, at Al2O3 nanoparticle content of 1.0wt%, according to neat epoxy. Due to lower cost and good mechanical properties of the Al2O3 nanoparticle-modified composites, the Al2O3 nanoparticle can be used as a reinforced particle for epoxy composites. On the other hand, it was observed that the CNTs were not as effective as Al2O3 nanoparticles.Öğe Determination of mechanical properties of polymer matrix composites reinforced with electrospinning N66, PAN, PVA and PVC nanofibers: A comparative study(Elsevier, 2021) Uslu, Emin; Gavgali, Mehmet; Erdal, Mehmet Okan; Yazman, Sakir; Gemi, LokmanFiber-reinforced polymer matrix composites are widely used in many structural applications thanks to their exceptional properties. In recent years, the use of electrospinning nanofibers with unique properties as reinforcement agents has attracted a great deal of attention in improving the performance of these composites. Although there are many promising studies on this subject in the literature, there are still many issues that need to be investigated. In this study, an experimental research reporting on the production and mechanical properties of two-phase polymer matrix composites reinforced with various types of thermoplastic nanofibers is presented. Nanofiber mats were produced from N66, PAN, PVA, and PVC polymers by electrospinning technique. Composites were obtained by embedding these nanofibers into epoxy resin by using vacuum infusion process. Mechanical properties of the composites were determined by performing tensile tests and the results were compared. The morphologies of nanofibers and the fracture surfaces of the composites were examined with SEM. Finally, statistical evaluations were carried out using mechanical data. According to tensile test results, the best ultimate tensile strength of 38.04 +/- 3.7 MPa, elongation of 2.46 +/- 0.4 % and toughness of 532 +/- 137 kJ/m(3) were obtained from N66 nanofiber composite, while PVA nanofiber composite was the most favorable in terms of Young's modulus (2.40 GPa). It was observed that the polymer type significantly affected the performance of the composite. In addition to the best mechanical properties, N66 composite was found to be more stable and reproducible than other specimens. Due to the good impregnation of nanofibers, it was conclusively determined that the use of vacuum infusion process is suitable for the production of these materials.Öğe Effect of Fiber Wrapping on Bending Behavior of Reinforced Concrete Filled Pultruded GFRP Composite Hybrid Beams(Mdpi, 2022) Gemi, Lokman; Madenci, Emrah; Ozkilic, Yasin Onuralp; Yazman, Sakir; Safonov, AlexanderThe application of pultruded fiber reinforced polymer (FRP) composites in civil engineering is increasing as a high-performance structural element or reinforcing material for rehabilitation purposes. The advantageous aspects of the pultrusion production technique and the weaknesses arising from the 0 degrees fiber orientation in the drawing direction should be considered. In this direction, it is thought that the structural performance of the profiles produced by the pultrusion technique can be increased with 90 degrees windings by using different fiber types. This paper presents experimental studies on the effect of FRP composite wrapping on the flexure performance of reinforced concrete (RC) filled pultruded glass-FRP (GFRP) profile hybrid beams with damage analysis. The hybrid beams are wrapped fully and partially with Glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) composites. Hybrid beam specimens with 0 degrees to 90 degrees fiber orientations were tested under three- and four-point bending loads. Based on the experimental load-displacement relationship results, initial stiffness, ductility, and energy dissipation capacity were compared. The experimental findings revealed that the maximum load-carrying capacities of beams produced with pultrude profiles increased by 24% with glass wrapping and 64.4% with carbon wrapping due to the change in the damages. A detailed damage analysis is provided. Similarly, significant increases were observed in structural performance ratios such as initial stiffness and ductility ratio.Öğe Effect of Silica/Graphene Nanohybrid Particles on the Mechanical Properties of Epoxy Coatings(Springer Heidelberg, 2019) Ozcan, Umit Esra; Karabork, Fazliye; Yazman, Sakir; Akdemir, AhmetEpoxy resins are used as coating materials, but the practical use of epoxy coatings in industries is limited due to their weak mechanical properties. In the present paper, different amounts of silica nanoparticles (SiO2) and graphene nanoplatelets (GNPs) were introduced separately and together into an epoxy coating matrix as reinforcements. Graphene, a newly discovered carbon allotrope, has been found to improve the mechanical properties of the polymer composites in which it is dispersed. Silica particles are also known to improve the mechanical properties of composites. In this study, mechanical, physical and thermal properties of the epoxy coatings are considered as multidimensional by the macro- and microanalyses. The experimental results showed that after the addition of GNPs into the epoxy matrix, the flexibility and impact resistance of the coatings increased by 8.3 and 157.1%, respectively, in relation to neat epoxy. The microhardness increased by 53.8% and penetration depth, which is indicative of the scratch resistance, decreased by 29.7%, with the addition of SiO2-GNPs nanohybrid. A remarkable synergistic effect was observed between the GNPs and SiO2, which improved the hardness and the scratch resistance of the epoxy coatings.Öğe Effects of high pulling speeds on mechanical properties and morphology of pultruded GFRP composite flat laminates(Elsevier Sci Ltd, 2022) Vedernikov, Alexander; Gemi, Lokman; Madenci, Emrah; Ozkilic, Yasin Onuralp; Yazman, Sakir; Gusev, Sergey; Sulimov, ArtemThe economic efficiency of pultrusion can be significantly improved by operating the process at higher pulling speeds. This experimental study analyzed the relationships between the pulling speed, morphology, and me-chanical properties of pultruded glass fiber/vinyl ester resin structural composites. Four batches of 150 mm x 3.5 mm flat laminates were produced at pulling speeds of 200, 600, 1000, and 1400 mm/min. Optical and scanning electron microscopy (SEM) were used to study the morphology of the produced flat laminates. The flexural and interlaminar shear properties were determined for both 0 degrees and 90 degrees fiber orientations. The observed difference in the mechanical characteristics of flat laminates can be explained by the presence of bubbles, lon-gitudinal voids, and matrix cracks and by an increase in their density and dimensions with an increase in pulling speed. This study is the first one to demonstrate the possibility of high speed pultrusion of large cross-section profiles suitable for structural application. Authors were able to achieve the pulling speed of 1000 mm/min, increasing the output by as much as 1.7 times as compared to the regular speed pultrusion, without compro-mising significantly the mechanical performance of produced profiles. The results of this study would be of assistance for a better understanding of high-speed pultrusion.Öğe Effects of nano reinforcing/matrix interaction on chemical, thermal and mechanical properties of epoxy nanocomposites(Sage Publications Ltd, 2021) Yazman, Sakir; Uyaner, Mesut; Karabork, Fazliye; Akdemir, AhmetThis article investigates the impact of addition various types of nanoparticles with different structural, dimensional, and morphological properties on the interphase region formed between the particle/matrix and the curing behavior of the epoxy affect the nanocomposite material properties. For this purpose, epoxy nanocomposites (NCs) were produced by adding multi-walled carbon nanotube (MWCNT) and alumina (Al2O3) nanoparticles (NPs) into the epoxy matrix at different rates (0.5-2.0 wt.%). The effects of the particle/matrix interaction on the properties of the composite have been revealed by chemical, thermal, mechanical analyzes and microstructure investigations. An increase in the absorption density, which reveals the physical interaction of nanoparticles with the epoxy matrix, was observed in Fourier-transform infrared spectroscopy. Absorption vibration peak intensities in nanocomposite samples were at most 1.0 wt.% Al2O3 and 1.25 wt.% CNT added nanocomposites. It was observed that the T-g value increased depending on the number of nanoparticles. The addition of Al2O3 increased T-g values more than CNT. Besides, the mechanical properties of NCs were determined by tensile tests. The highest increase in mechanical properties was achieved by adding 1.25 wt.% CNT and 1.0 wt.% Al2O3, respectively. Mechanical properties tended to decrease at higher addition rates. The shape, size, amount, and distribution of nanoparticles added into the epoxy matrix directly affected the NCs' properties. It has been determined that homogeneously dispersed spherical Al2O3 nanoparticles are more effective than fiber-shaped CNTs in the properties of NCs.Öğe The effects of stacking sequence on drilling machinability of filament wound hybrid composite pipes: Part-1 mechanical characterization and drilling tests(Elsevier Sci Ltd, 2020) Gemi, Lokman; Koklu, Ugur; Yazman, Sakir; Morkavuk, SezerIn the first part of this two-part comprehensive study, mechanical properties and machinability characteristic of filament wound hybrid composite pipes with various stacking sequences of glass and carbon fibers (Glass-Carbon-Glass (GCG), Carbon-Glass-Glass (CGG), and Glass-Glass-Carbon (GGC)) were investigated experimentally. In order to determine the mechanical properties of the pipes, hardness test (Shore D), ring tensile test (ASTM D2290), and burst test (ASTM D1599) were carried out. Machinability tests were performed at various feed rates (50, 150, 250 and 350 nun/min) and spindle speeds (796, 1592, 2388 and 3184 rpm) using with and without a back-up. The results showed that stacking of the carbon layer between two glass layers (GCG) presented better performance in terms of mechanical properties and machinability characteristic. The maximum ring tensile stress of GCG specimen is 27% and 19% higher than those of GGC and CGG specimens, respectively. On the other hand, the lowest thrust forces measured during the drilling of GCG specimen while the GGC represented highest values. In addition, the use of back-up led to an increase in thrust force. The highest increase was observed in GGC sample. In GGC sample, a change in a spindle speed increased thrust force by 18-35%, while a change in feed rate increased thrust force by 20-30%.Öğe The effects of stacking sequence on drilling machinability of filament wound hybrid composite pipes: Part-2 damage analysis and surface quality(Elsevier Sci Ltd, 2020) Gemi, Lokman; Morkavuk, Sezer; Koklu, Ugur; Yazman, SakirIn the first part of this two-part study, filament wound hybrid composite pipes with various stacking sequences were manufactured and mechanical properties such as hardness, ring tensile strength, and burst strength were experimentally investigated. After determining mechanical properties, drilling tests were performed to research machinability characteristics. The second part of the study consists damage analysis and surface quality examination including ring test damage analysis, push-out delamination analysis, borehole damage examination and borehole surface quality. The experimental data suggested that cutting parameters, stacking sequence, and the use of back-up were impactful on the formation and propagation of various types of damages. Especially, the effect of stacking sequence was remarkable. A larger delamination area was formed in Glass-Glass-Carbon (GGC) sample after the ring tensile tests compared to Glass-Carbon-Glass (GCG) and Carbon-Glass-Glass (CGG) samples. In all cases, the utilization of back-up lead to decrease of delamination with 9-40% reduction in surface roughness. When the back-up is not used during drilling, an excessive push-out delamination occurred in all drilling tests. Moreover, CGG samples represented lower push out delamination. In addition, position of the hole depending on the winding angle plays a key role on damage formation and surface quality.Öğe Experimental analysis of reinforced concrete shear deficient beams with circular web openings strengthened by CFRP composite(Elsevier Sci Ltd, 2020) Aksoylu, Ceyhun; Yazman, Sakir; Ozkilic, Yasin Onuralp; Gemi, Lokman; Arslan, Musa HakanIn this study, two methods of CFRP applications were utilized to strengthen the shear deficient beams with cir-cular holes and a comprehensive experimental program consisting of 11 1/2 scaled specimens was undertaken. The beams with hole diameter (D)/beam height ratio (H) of 0.30, 0.44, 0.64 ratios, symmetrically drilled in shear span were tested under vertical loading. D/H ratio of 0.30 did cause not only a decrease in load carrying capacity but also increased the ductility of the beam. However, significant decreases in load carrying capacities were observed as the hole diameters increase. The load carrying capacity and ductility were significantly improved owing to different CFRP configurations. The fact that the hole diameter and CFRP strengthening method are very important parameters for strengthening is observed. No CFRP strengthening alternative was successful in the beams with a D/H ratio of 0.64. A detailed macro and micro damage analyses are presented.Öğe Experimental investigation of shear capacity and damage analysis of thinned end prefabricated concrete purlins strengthened by CFRP composite(Elsevier Sci Ltd, 2019) Gemi, Lokman; Aksoylu, Ceyhun; Yazman, Sakir; Ozkilic, Yasin Onuralp; Arslan, Musa HakanPrefabricated structures supported with purlins are exposed to numerous damages due to the excessive snow loadings as vertical loadings. The thinned regions of the purlins are responsible with the failure of the structure since the shear cracks usually initiate at these regions and propagate along with the purlins, and as a result, a total collapse may occur. In this study, carbon fiber reinforced polymer (CFRP) composites with four different configurations (P-2-P-5) were employed for strengthening prefabricated purlins in order to increase the strength of the purlin against shear damage generated under vertical loading. The load carrying capacities and damage patterns of the purlins were compared. The failure of the reference purlin (P-1) was occurred as a shear damage at the thinned regions before reaching its bending capacity. However, the failure characteristic of the CFRP reinforced purlins was dominated by the bending damage and the vertical loading capacity of the purlins were increased up to 59% depends on the CFRP wrapping. Damage analysis of the CFRP composite was also performed. Various damage modes of the structure such as cover separation, air voids, delamination, debonding, fiber bundles breakage, matrix cracks, fiber bundles debonding, fiber breakage and buckling were observed and explained thoroughly.Öğe Experimental study on the effects of cold chamber die casting parameters on high-speed drilling machinability of casted AZ91 alloy(Elsevier Sci Ltd, 2020) Yazman, Sakir; Koklu, Ugur; Urtekin, Levent; Morkavuk, Sezer; Gemi, LokmanIn this study, the effects of the cold chamber die casting parameters on high-speed drilling machinability of AZ91 Magnesium alloys were experimentally investigated. The influence of different casting parameters (casting temperature, molding pressure, and gate speed) on microstructure, mechanical properties and machinability characteristics (thrust force, tool wear, built-up edge, built-up layer formation, surface topography, chip morphology, and burr formation) were examined. The experimental results showed that the grain size of the conventional casting sample was around 50 microns, while in other cold chamber die casting tests, it varied depending on temperature, pressure, and gate speed. It was observed that the tensile strength values of the samples produced with 1000 bar mold pressure were higher than those of other samples. In the formation of thrust force, the feed rate is more effective than the cutting speed. The least tool wear occurred in the drilling of the As-cast sample, while the highest tool wear occurred in the drilling of the sample which was produced with low pressure and low gate speed combination. As a result of the drilling tests, depending on casting and cutting parameters, three different types of chips were formed: fan, spiral cone, and long ribbon type. Furthermore, uniform and transient burrs in different sizes were observed.Öğe Investigation Effect of Zinc Nanoparticles on The Mechanical and Anticorrosion Properties of Epoxy Coatings on Stainless Steel Surface(Gazi Univ, 2021) Apsak, Merve; Akdemir, Ahmet; Karabork, Fazliye; Yazman, SakirIn this study, effects of zinc nanoparticles (ZNPs) on the mechanical properties of epoxy coatings and anticorrosion behavior on the stainless steel were investigated. The nanocomposites (NCs) were obtained by adding ZNPs (0.5, 1.0, 1.5 wt%) to epoxy resin. The first stage in this study, bulk samples were prepared for tensile test and DSC, TGA, FTIR, SEM analysis. The test and analysis were performed separately for samples cured at room temperature for 24 h and postcured at 80 degrees C for 15 h in the oven. The results indicated that both postcuring and adding ZNPs caused an increase in the mechanical properties of the epoxy matrix. Tensile strength increased by 13.2% and 90.2% in the postcured NC (1.0% Zn) and untreated NC (0.5% Zn) respectively. The NCs prepared with the same parameters for the second stage were coated on AISI 304 test panels and the panels were postcured in the oven. The anticorrosive performance of the coatings was studied by an immersion test. According to the corrosion test results, it was observed that the coated steel surface preserves the best rate of 1.0% ZNPs containing epoxy composite. In addition, impact resistance, flexibilities and adhesion properties of the coating were analyzed.Öğe Numerical and analytical investigation of parameters influencing the behavior of shear beams strengthened by CFRP wrapping(Techno-Press, 2023) Aksoylu, Ceyhun; Ozkilic, Yasin Onuralp; Yazman, Sakir; Alsdudi, Mohammed; Gemi, Lokman; Arslan, Musa HakanIn this study, a parametric study was performed considering material properties of concrete, material properties of steel, the number of longitudinal reinforcement (reinforcement ratio), CFRP ply orientations, a number of layers as variables by using ABAQUS. Firstly, the parameters used in the Hashin failure criteria were verified using four coupon tests of CFRP. Secondly, the numerical models of the beams strengthened by CFRP were verified using five experimental data. Finally, eighty numerical models and eighty analytic calculations were developed to investigate the effects of the aforementioned variables. The results revealed that in the case of using fibrous polymer to prevent shear failure, the variables related to reinforced concrete significantly affected the behavior of specimens, whereas the variables related to CFRP composite have a slight effect on the behavior of the specimens. As a result of numerical analysis, while the increase in the longitudinal tensile and compression reinforcement, load bearing capacity increases between 23.6%-70.7% and 5.6%-12.2%, respectively. Increase in compressive strength (29 MPa to 35 MPa) leads to a slight increase in the load-carrying capacity of the specimens between 4.6% and 7.2%. However, the decrease in the compressive strength (29 MPa to 20 MPa) significantly affected (between 6.4% and 8.1% decrease observed) the behavior of the specimens. As the yield strength increases or decreases, the capacity of specimens increase approximately 27.1% or decrease 12.1%. The effects of CFRP ply orientation results have been obtained as a negligible well approximately 3.7% difference. An increasing number of CFRP layers leads to almost no effect (approximately 2.8%) on the behavior of the specimen. Finally, according to the numerical analysis, the ductility values obtained between 4.0 and 6.9 indicate that the beams have sufficient ductility capacity.Öğe Numerical and analytical investigation of parameters influencing the behavior of shear beams strengthened by CFRP wrapping(Techno-Press, 2023) Aksoylu, Ceyhun; Ozkilic, Yasin Onuralp; Yazman, Sakir; Alsdudi, Mohammed; Gemi, Lokman; Arslan, Musa HakanIn this study, a parametric study was performed considering material properties of concrete, material properties of steel, the number of longitudinal reinforcement (reinforcement ratio), CFRP ply orientations, a number of layers as variables by using ABAQUS. Firstly, the parameters used in the Hashin failure criteria were verified using four coupon tests of CFRP. Secondly, the numerical models of the beams strengthened by CFRP were verified using five experimental data. Finally, eighty numerical models and eighty analytic calculations were developed to investigate the effects of the aforementioned variables. The results revealed that in the case of using fibrous polymer to prevent shear failure, the variables related to reinforced concrete significantly affected the behavior of specimens, whereas the variables related to CFRP composite have a slight effect on the behavior of the specimens. As a result of numerical analysis, while the increase in the longitudinal tensile and compression reinforcement, load bearing capacity increases between 23.6%-70.7% and 5.6%-12.2%, respectively. Increase in compressive strength (29 MPa to 35 MPa) leads to a slight increase in the load-carrying capacity of the specimens between 4.6% and 7.2%. However, the decrease in the compressive strength (29 MPa to 20 MPa) significantly affected (between 6.4% and 8.1% decrease observed) the behavior of the specimens. As the yield strength increases or decreases, the capacity of specimens increase approximately 27.1% or decrease 12.1%. The effects of CFRP ply orientation results have been obtained as a negligible well approximately 3.7% difference. An increasing number of CFRP layers leads to almost no effect (approximately 2.8%) on the behavior of the specimen. Finally, according to the numerical analysis, the ductility values obtained between 4.0 and 6.9 indicate that the beams have sufficient ductility capacity.Öğe Numerical investigation of the parameters influencing the behavior of dapped end prefabricated concrete purlins with and without CFRP strengthening(Elsevier Sci Ltd, 2021) Ozkilic, Yasin Onuralp; Yazman, Sakir; Aksoylu, Ceyhun; Arslan, Musa Hakan; Gemi, LokmanDapped end prefabricated concrete purlins (PCPs) suffer from shear damages due to coating, snow, wind load and also their dead loads. In this present study, a series of numerical modelling is performed with the aid of finite element program ABAQUS in order to investigate this behavior of PCPs through parametric study. In addition to the mechanical properties of the PCPs, the strengthening of the PCPs with the help of carbon fiber reinforced polymers (CFRP) is considered as a parameter in the models. Pursuant to this aim, longitudinal steel reinforcement ratio, shear friction reinforcement ratio, bending reinforcement ratio, suspension reinforcement ratio, concrete and steel mechanical properties, pre-stressing level, CFRP ply orientation, the number of CFRP plies and material properties of CFRP composite were selected as the parameters. First of all, numerical models were verified using experimental test data of three PCP test specimens and five CFRP coupon tests. Later, a total of 50 different numerical models was created to investigate the behavior of PCPs thoroughly. Vertical load- displacements curves are compared and explained in detail. The result of the parametric study revealed that the effects of the parameters related to reinforced concrete except longitudinal reinforcement and material properties of concrete are very limited when compared to the effects of the parameters related to CFRP. The effect of FRP ply orientation is the most effective parameter that increases significantly the shear capacity of PCPs. More importantly is the general FRP layout is proposed to delay or prevent shear cracks for the beams and the proposed layout is proved through numerical analyses. [+/- 45 degrees] fiber orientation is recommended to use to prevent shear damage. (C) 2020 Elsevier Ltd. All rights reserved.Öğe Optimum amount of CFRP for strengthening shear deficient reinforced concrete beams(Techno-Press, 2022) Gemi, Lokman; Alsdudi, Mohammed; Aksoylu, Ceyhun; Yazman, Sakir; Ozkilic, Yasin Onuralp; Arslan, Musa HakanThe behavior of shear deficient under-balanced reinforced concrete beams with rectangular cross-sections, which were externally strengthened with CFRP composite along shear spans, was experimentally investigated under vertical load. One of the specimens represents a reference beam without CFRP strengthening and the other specimens have different width/strip spacing ratios (w(f)/s(f)). The optimum strip in terms of w(f)/s(f), which will bring the beam behavior to the ideal level in terms of strength and ductility, was determined according to the regulations. When the w(f)/s(f) ratio exceeds 0.55, the behavior of the beam shifted from shear failure to bending failure. However, it has been observed that the w(f)/s(f) ratio should be increased up to 0.82 in order for the beam to reach sufficient shear reserve value according to the codes. It is also observed that the direction and weight of the CFRP composite are one of the most critical factors and 240 gr/m(2) CFRP strips experienced sudden ruptures in the shear span after the cracking of the concrete. It is considered as a deficiency that the empirical shear capacity formulas given for the beams reinforced with CFRP in the regulations do not take into account both direction and weight of CFRP composites.Öğe Optimum amount of CFRP for strengthening shear deficient reinforced concrete beams(Techno-Press, 2022) Gemi, Lokman; Alsdudi, Mohammed; Aksoylu, Ceyhun; Yazman, Sakir; Ozkilic, Yasin Onuralp; Arslan, Musa HakanThe behavior of shear deficient under-balanced reinforced concrete beams with rectangular cross-sections, which were externally strengthened with CFRP composite along shear spans, was experimentally investigated under vertical load. One of the specimens represents a reference beam without CFRP strengthening and the other specimens have different width/strip spacing ratios (w(f)/s(f)). The optimum strip in terms of w(f)/s(f), which will bring the beam behavior to the ideal level in terms of strength and ductility, was determined according to the regulations. When the w(f)/s(f) ratio exceeds 0.55, the behavior of the beam shifted from shear failure to bending failure. However, it has been observed that the w(f)/s(f) ratio should be increased up to 0.82 in order for the beam to reach sufficient shear reserve value according to the codes. It is also observed that the direction and weight of the CFRP composite are one of the most critical factors and 240 gr/m(2) CFRP strips experienced sudden ruptures in the shear span after the cracking of the concrete. It is considered as a deficiency that the empirical shear capacity formulas given for the beams reinforced with CFRP in the regulations do not take into account both direction and weight of CFRP composites.Öğe Relationship Between Machinability, Microstructure, and Mechanical Properties of Al-7Si Alloy(Amer Soc Testing Materials, 2018) Uludag, Muhammet; Yazman, Sakir; Gemi, Lokman; Bakircioglu, Baris; Erzi, Eray; Dispinar, DeryaIn this work, commercially available Al-7Si alloy was used, and the microstructure was modified by the additions of AlSr15, AlTi5B1, and Al3B. Cylindrical samples were cast into a sand mold and the machinability of the alloys was characterized by means of surface roughness, chip morphology, and buildup edge of the chips. Tool life and surface finish can be improved by decreased chip size by lowering the energy required for machining. The surface finish is an indicator of the quality of the material during the machining process. Therefore, in addition, melt quality was measured by means of reduced pressure test and the calculation of the bifilm index was used to compare the melt quality with machinability. It was found that there is a good correlation between bifilm index and surface roughness of the machined parts. Thus, for a better surface finish, melt quality, which can be quantified by bifilm index, has to be high. AlSr15 modified alloy exhibits the lowest built-up edge with the lowest surface roughness, because strontium modification causes coarse silicon crystals to transform to fine fibrous structure, which enhances machinability.Öğe Relationship Between Machinability, Microstructure, and Mechanical Properties of Al-7Si Alloy(Amer Soc Testing Materials, 2018) Uludag, Muhammet; Yazman, Sakir; Gemi, Lokman; Bakircioglu, Baris; Erzi, Eray; Dispinar, DeryaIn this work, commercially available Al-7Si alloy was used, and the microstructure was modified by the additions of AlSr15, AlTi5B1, and Al3B. Cylindrical samples were cast into a sand mold and the machinability of the alloys was characterized by means of surface roughness, chip morphology, and buildup edge of the chips. Tool life and surface finish can be improved by decreased chip size by lowering the energy required for machining. The surface finish is an indicator of the quality of the material during the machining process. Therefore, in addition, melt quality was measured by means of reduced pressure test and the calculation of the bifilm index was used to compare the melt quality with machinability. It was found that there is a good correlation between bifilm index and surface roughness of the machined parts. Thus, for a better surface finish, melt quality, which can be quantified by bifilm index, has to be high. AlSr15 modified alloy exhibits the lowest built-up edge with the lowest surface roughness, because strontium modification causes coarse silicon crystals to transform to fine fibrous structure, which enhances machinability.
