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Öğe An elastic-plastic and residual stress analysis steel reinforced thermoplastic composite cantilever beam(2010) Aykul, Halil; Kaya, SamiIn the present study an analytical elastic-plastic stress analysis is carried out for a low-density homogeneous polyethylene thermoplastic cantilever beam reinforced by steel fibers. The beam is loaded by a constant single force at its free end. The expansion of the region and the residual stress component of ?x are determined for 0°, 15°, 30°, 45°, 60°, 75° and 90° orientation angles. Yielding begins for 0° and 90° orientation angles at the upper and lower surfaces of the beam at the same distances from the free end. Although it starts first at the upper surface for 15°, 30° and 45°, it starts first at the lower surface for 60° and 75° orientation angles. The elastic-plastic analysis is carried out for both the plastic region which spreads only at the upper surface and the plastic region which spreads at the upper and lower surfaces together. The residual stress components of ?x and ?xy are also determined. The intensity of the residual stress component is maximum at the upper and lower surfaces of the beam, but the residual stress component of ?xy is maximum on or around the kh{cyrillic}-axis. The beam can be strengthened by using the residual stresses. The distance between the plastically collapsed point and the free end is calculated for the same load in the beam for 0°, 15°, 30°, 45°, 60°, 75° and 90° orientation angles. © 2010 Elsevier Ltd.Öğe An elastic-plastic stress analysis of woven Ni-Cr reinforced thermoplastic composite cantilever beam(2007) Aykul, Halil; Sayman, OnurIn the present study an analytical elastic-plastic stress analysis is carried out for a low-density homogeneous polyethylene thermoplastic cantilever beam reinforced by Ni-Cr steel fibers. The beam is loaded by a constant single force at its free end. The expansion of the region and the residual stress component of ?x are determined for 0°, 15 ° , 30° and 45° orientation angles. For 0° and 45° orientation angles yielding begins at the upper and lower surfaces of the beam, at the same distances from the free end. However, for 15° and 30° orientation angles it starts first at the upper surface. The elastic-plastic analysis is carried out for both the plastic region which spreads only at the upper surface and the plastic region which spreads at the upper and lower surfaces together. The residual stress components of ?x and ?xy are also determined. The intensity of the residual stress component is maximum at the upper and lower surfaces of the beam, but the residual stress component of ?xy is maximum on or around the x-axis. The beam can be strengthened by using the residual stresses. The distance between the plastically collapsed point and the free end is calculated for the same load in the beam for 0°, 15°, 30° and 45° orientation angles. © SAGE Publications 2007.Öğe An elastic-plastic stress analysis steel-reinforced thermoplastic composite cantilever beam(2008) Aykul, Halil; Yılmaz, Selim SarperIn the present study an analytical elastic-plastic stress analysis is carried out for a low-density homogeneous polyethylene thermoplastic cantilever beam reinforced by steel fibers. The beam is loaded by a constant single force at its free end. The expansion of the region and the residual stress component of ?x are determined for 0°, 30°, 45°, 60° and 90° orientation angles. Yielding begins for 0° and 90° orientation angles at the upper and lower surfaces of the beam at the same distances from the free end. However, it starts first at the upper surface for 30° and 45° orientation angles. The elastic-plastic analysis is carried out for both the plastic region which spreads only at the upper surface and the plastic region which spreads at the upper and lower surfaces together. The residual stress components of ?x and ?xy are also determined. The intensity of the residual stress component is maximum at the upper and lower surfaces of the beam, but the residual stress component of ?xy is maximum on or around the x-axis. The beam can be strengthened by using the residual stresses. The distance between the plastically collapsed point and the free end is calculated for the same load in the beam for 0°, 30°, 45°, 60° and 90° orientation angles. © 2007 Elsevier Ltd. All rights reserved.Öğe Computed tomography analysis of impact response of lightweight sandwich panels with micro lattice core(SAGE Publications Ltd, 2018) Abrate, Serge; Epasto, Gabriella; Kara, Emre; Crupi, Vincenzo; Guglielmino, Eugenio; Aykul, HalilOne of the main focuses in transportation engineering is the application of sandwich materials in order to create safer and efficient vehicles. The main focus of this study was the application of 3D computed tomography for analyzing the responses of sandwich panels with micro lattice core subjected to impact loading. Micro lattice specimens were manufactured using Ti-6Al-4V powder by means of a direct metal laser sintering system. A theoretical model was applied for predicting the failure initiation loads under impact loading. The predictions presented good consistency with the experimental measurements. The 3D computed tomography system was used for the analysis of the collapse modes of the micro lattice sandwich panels after low-velocity impact tests. Experimental and theoretical results proved that lightweight sandwich panels with micro lattice cores are excellent energy absorbers and, therefore, they could have significant applications in the transportation industry. © 2018, © IMechE 2018.Öğe Effect of different palatal vault shapes on the dimensional stability of glass fiberreinforced heat-polymerized acrylic resin denture base material(2012) Dalkız, Mehmet; Arslan, Demet; Tunçdemir, Ali Rıza; Bilgin, M. Selim; Aykul, HalilObjective: The aim of this study was to determine the effect of different palatal vault shapes on the dimensional stability of a glass fiber reinforced heat polymerized acrylic resin denture base material. Methods: Three edentulous maxilla with shallow, deep and medium shaped palatal vaults were selected and elastomeric impressions were obtained. A maxillary cast with four reference points (A, B, C, and D) was prepared to serve as control. Point (A) was marked in the anterior midline of the edentulous ridge in the incisive papillary region, points (B) and (C) were marked in the right and left posterior midlines of the edentulous ridge in the second molar regions, and point (D) was marked in the posterior palatal midline near the fovea palatina media (Figure 2). To determine linear dimensional changes, distances between four reference points (A-B, A-C, A-D and B-C) were initially measured with a metal gauge accurate within 0.1 mm under a binocular stereo light microscope and data (mm) were recorded. Results:No significant difference of interfacial distance was found in sagittal and frontal sections measured 24 h after polymerization and after 30 days of water storage in any of experimental groups (P>.05). Significant difference of linear dimension were found in all experimental groups (P<.01) between measurements made 24 h after polymerization of specimens and 30 days after water storage. Conclusion: Palatal vault shape and fiber impregnation into the acrylic resin bases did not affect the magnitude of interfacial gaps between the bases and the stone cast surfaces.Öğe Evaluation of the effects of surface treatments on different dental ceramic structures(2013) Ertürk, Ergül; Dalkız, Mehmet; Özyılmaz, Emre; Akbaş, H. Zehra; Çetinkara, H. Ali; Aykul, HalilThe surface treatments applied to porcelain materials can be different overglaze methods, chemical interactions and polishing techniques. The aims of these methods are the most durable restoration and the smoothest surface. The smoothness attained with these processes is important due to the following reasons: reduction of the bacteria remaining in the pores of a surface, improvement of gingival health and esthetic view, and prevention of an abrasion of the opposite canal. The aim of this study is to assess different surface-finishing operations that are applied to widely used porcelains in prosthetic dentistry using SEM (a scanning electron microscope). In the experiments seven different surface finishing operations (sandpaper, rubber, Sof-Lex, HP paste, autoglaze, overglaze and ion exchange) were applied to four different commercial porcelains (IPS d. SIGN, Antagon, Ceramco 3, Vitadur Alpha).The effects of various surface-finishing operations on porcelain are micromorphologically evaluated (a SEM analysis). The results showed that the smoothest surfaces were obtained with the overglaze and autoglaze, followed by HP paste, rubber, Sof-Lex and sandpaper. In addition, the smoothness values of HP paste proved that it can be safely used in clinical surface-finishing operations.Öğe Fatigue behavior of adhesively bonded glass fiber reinforced plastic composites with different overlap lengths(SAGE Publications Ltd, 2015) Kara, Emre; Kurşun, Ali; Haboğlu, Mustafa Reşit; Enginsoy, Halil Murat; Aykul, HalilThe joining techniques of lightweight and strong materials in the transport industry (e.g. automotive, aerospace, shipbuilding industries) are very important for the safety of the entire structure. In these industries, when compared with other joining methods, the use of adhesively bonded joints presents unique properties such as greater strength, design flexibility, and reduction in fuel consumption, all thanks to low weight. The aim of this study was the analysis of the tensile fatigue behavior of adhesively bonded glass fiber/epoxy laminated composite single-lap joints with three different specimen types including 30, 40 and 50mm overlap lengths. In this study, composite adherents were manufactured via vacuum-assisted resin transfer molding and were bonded using Loctite 9461A&B toughened epoxy adhesive. The effect of a surface treatment method on the bonding strength was considered and it led to an increment of about 40%. A numerical analysis based on a finite element model was performed to predict fatigue life curve, and the predicted results showed good agreement with the experimental investigation. © IMechE 2015.Öğe Flexural behaviour of glass fiber reinforced aluminium honeycomb sandwiches in flatwise and edgewise positions(European Conference on Composite Materials, ECCM, 2014) Kara, Emre; Crupi, Vincenzo; Epasto, Gabriella; Guglielmino, Eugenio; Aykul, HalilThe goal of this research was the analysis of edgewise bending response of sandwiches, which consists of aluminium honeycomb sandwich reinforced by outer skins made of glass fiber reinforced epoxy matrix. The test results at different values of support span distances in terms of peak loads and absorbed energy were compared with those obtained by flatwise bending tests and by similar tests on aluminium honeycomb sandwiches without outer skins. The failure mechanisms have been also investigated. The experimental results presented that the sandwiches in the edgewise position failed at a higher load with less deflection compared to the specimens tested in the flatwise position. The current work has an important role in several areas, such as transport industry, in which lightweight structures with high capacity of energy dissipation is required.Öğe Impact response of sandwiches with open-cell casting metal foam and GFRP skins(Taylor and Francis Ltd., 2016) Kurşun, Ali; Kara, Emre; Aykul, Halil; Şenel, Mehmet; Ağır, İnanThe main advantage of using sandwich structures is their high strength, high energy absorbing capacity and high bending stiffness to weight ratio. Therefore, they are unique for the applications where the light-weight design philosophy is a crucial aspect. While sandwich structures with polymeric foams have been applied for many years, recently there is a growing interest on a new generation composite sandwiches with metallic foam core. In this study, the influence of pores per inch (ppi) of the foam on low-velocity impact response of the entire panel has been investigated. The glass fibre reinforced plastic (GFRP) skins produced by vacuum bagging technique in the study were easily bonded to the foam surfaces using a commercial adhesive in order to combine the composite sandwich panel. The low-velocity impact tests are performed to the sandwiches with the combination of two different magnesium (Mg) alloy foams (having 10 pores per inch (ppi) and 20 pores per inch), and carried out by a drop test machine with different values of impact velocity ranging from 1 to 10 m/s in order to analyse its effect. The main results of the impact tests are: force-displacement curves, peak force values, absorbed energy and influence of impact velocity. © 2016, © 2016 Informa UK Limited, trading as Taylor & Francis Group.Öğe Investigation of the effect of temperature on the mechanical properties of E-Glass fiber reinforced composites(The Composites and Advanced Materials Expo (CAMX), 2014) Haboğlu, Mustafa Reşit; Kurşun, Ali; Kara, Emre; Çetin, Erhan; Aykul, HalilIn this study, mechanical characterization of E-Glass fiber reinforced composite materials that are manufactured via Vacuum Infusion (VI) (a.k.a Vacuum Assisted Resin Transfer Molding (VARTM)) is investigated. The mechanical properties are analyzed at different temperatures (23 oC (room temperature), 40 °C, 60 °C, 80 °C, 100 °C) by using a universal tensile testing machine integrated with a heat chamber. The mechanical tests are performed for 3 different reinforcement types such as (i) plain woven, (ii) biaxial stiched and (iii) quadraxial stiched E-Glass fabrics. The result of this study provides a database for applications that use composite materials at different temperatures.Öğe Investigation of the Effects of Abutment and Implant Length on Stability of Short Dental Implants(2014) Özyılmaz, Eda; Aykul, Halil; Ozyılmaz, Emre; Dalkız, Mehmet; Bilgin, M. BurakDiş hekimliğinde bulunan farklı sorunları çözmek için dental implantların kullanımı hızla artmaktadır. Dental implantların başarı oranları da hastalar için oldukça önemlidir. Kısa dental implantlar, hastaların kemik seviyesine bağlı olarak çok popüler ve yaygın olarak pek çok diş hekimleri tarafından kullanılmaktadır. Birçok diş hekimi sık sık kısa diş implantları kullanmasına rağmen, implant-kron oranlarından dolayı stabilite sorunlarının gerçekleşebileceği tahmin edilebilir. Bu çalışmada, implant ve abutment uzunluklarının kısa dental implantlardaki stabilite üzerine etkilerinin incelenmesi amaçlanmıştır. Üç farklı kısa implant tasarımı Solidworks 2013 programı kullanılarak tasarlanmıştır. Her bir model için abutment uzunlukları 3,5 mm, 4 mm, 4,5 mm ve 5 mm, implant uzunlukları da 5 mm, 6 mm, 7 mm olarak tasarlanmıştır. Insan çene kemiği Bilgisayarlı tomografi görüntülerinden transfer edilmiştir. Her bir implant modeli çene kemiğine implante edilerek Sonlu Elemanlar Analiz yöntemiyle analiz edilmiştir. İmplant sayısının stabilite üzerindeki etkisini görmek amacıyla, tamamen dişsiz çeneye 4 adet implant yerleştirilerek analiz gerçekleştirilmiştir.Öğe Low velocity impact response of glass fiber reinforced aluminium foam sandwich(European Conference on Composite Materials, ECCM, 2012) Kara, Emre; Crupi, Vincenzo; Epasto, Gabriella; Guglielmino, Eugenio; Aykul, HalilThe aim of this study was the analysis of the bending and the low - velocity impact response of aluminium foam sandwich reinforced by the outer skins made of glass fiber reinforced epoxy matrix and the results were compared with those obtained for aluminium foam sandwiches without glass fiber skins. Static bending tests were carried on panels with the same nominal size at different support span distances in order to analyze the collapse modes and their capacity of absorbing energy, while the energy amount absorbed under dynamic loading was evaluated by means of impact tests. The experimental investigation has particular importance for applications which require lightweight structures with a high capacity of energy dissipation, such as transport industries.Öğe Prediction model for the impact response of glass fibre reinforced aluminium foam sandwiches(Elsevier Ltd, 2015) Crupi, Vincenzo; Kara, Emre; Epasto, Gabriella; Guglielmino, Eugenio; Aykul, HalilThe use of sandwich structures combines low weight with high energy absorbing capacity, so they are suitable for applications in the transport industry (automotive, aerospace, shipbuilding industry), where the "lightweight design" philosophy and the safety of vehicles are very important aspects. The goal of this paper was the analysis of the bending and the low - velocity impact response of aluminium foam sandwiches reinforced by the outer skins made of glass fibre reinforced epoxy matrix. The results were compared with those obtained for aluminium foam sandwiches without glass fibre skins. An analytical model for the peak load prediction under low velocity impact was developed and the predicted values are in good agreement with the experimental measurements. The impact response of the sandwiches was investigated using a theoretical approach, based on the energy balance model and the model parameters were obtained by the tomographic analyses of the impacted panels. This combined experimental and theoretical investigation has particular importance for applications that require lightweight composite structures with a high capacity of energy dissipation, such as the transport industry, where problems of collision and crash have increased in the last years. © 2014 Elsevier Ltd. All rights reserved.Öğe Residual stress analysis and expansion of plastic zone in simple supported woven Ni-Cr reinforced thermoplastic matrix composite laminated plates(2006) Aykul, HalilIn this study, a residual stress analysis is carried out on symmetric and antisymmetric cross-ply and angleply thermoplastic simple supported laminated plates for transverse loading. Low density polyethylene thermoplastic matrix (LDPE) and woven Ni-Cr fibers are used to produce the composite plates by using moulds. First order shear deformation theory and nine nodes Lagrangian finite element are used. A mathematical formulation is given for the elasto-plastic stress analysis of a laminated plate for small deformations. Yield points and stresses are obtained for symmetric and antisymmetric simple supported laminated plates with a square hole. Residual stresses in thermoplastic plates are given in tables. The expansion of plastic zones is illustrated for 200, 400 and 600 loading steps. Yield points and the expansion of plastic zones are compared for different plates. Mechanical properties of a layer are obtained experimentally. The intensity of the residual stress components is maximum near the square hole. © Freund Publishing House Ltd.Öğe Residual stress analysis of aluminum metal matrix composite laminated plates with a square hole(2009) Aykul, Halil; Özdin, KamilMetal matrix composites provide new materials with superior properties. They give high strength and stiffness. In this study, a stainless steel reinforced aluminum metal matrix laminated simple supported plate with a square hole is loaded transversely. Elastic, plastic, and residual stress analysis are calculated in the symmetric and antisymmetric cross-ply and angle-ply laminated plates for small deformations by using finite elements method. First-order shear deformation theory and nine nodes Lagrangian finite element are used. Load steps are chosen at 200, 400, and 600. Mechanical properties of a layer are obtained experimentally. The change of the residual stresses ?x and ?y from square hole to simple supported edge are shown as figures. © 2009 SAGE Publications.Öğe Residual stress analysis snd expansion of plastic zone in simple supported and clamped supported woven Ni-Cr reinforced thermoplastic matrix composite laminated plates(2007) Aykul, Halil; Uzkut, MehmetIn this study, a residual stress analysis is carried out on symmetric cross-ply and angle-ply thermoplastic simple supported and clamped supported laminated plates for transverse loading. Low density polyethylene thermoplastic matrix (LDPE) and woven NiCr fibers are used to produce the composite plates by using molds. First order shear deformation theory and nine nodes Lagrangian finite element are used. Mathematical formulation is given for the elasto-plastic stress analysis of a laminated plate for small deformations. Yield points and stresses are obtained for symmetric simple supported and clamped supported laminated plates. Residual stresses in thermoplastic plates are given in the tables. The expansion of plastic zones is illustrated for 50, 100 and 150 loading steps. Yield points and the expansion of plastic zones are compared for different plates. Mechanical properties of a layer are obtained experimentally. © 2007 SAGE Publications.Öğe Static behavior of lattice structures produced via direct metal laser sintering technology(Elsevier Ltd, 2017) Crupi, Vincenzo; Kara, Emre; Epasto, Gabriella; Guglielmino, Eugenio; Aykul, HalilThe aim of this scientific work was the analysis of the micro lattice structures under uniaxial quasi-static compression loading with regard to the effect of unit cell size and strut diameter. A wide range of cubic lattice blocks designed in a CAD software were fabricated using Ti6Al4V (Ti64) metal powder and two different production parameters in the direct metal laser sintering machine. The failure modes of the specimens were investigated and the 3D Computed Tomography system was used for the morphological analysis of the struts. An analytical model, developed by Gibson and Ashby, was adapted to the titanium body centered cubic lattices in order to predict their mechanical properties for compressive loading. Moreover, the compressive responses of the lattice structures were also studied using a numerical approach based on finite element analysis. Both experimental and theoretical results presented good agreement in terms of mechanical properties of the body centered cubic lattices and showed that such structures are great energy absorbers. Theoretical approaches gave significant results on the predictions of mechanical properties of these cellular structures, which are suitable for biomedical and transport engineering applications, in order to save manufacturing cost and time. © 2017 Elsevier LtdÖğe Theoretical and experimental analysis for the impact response of glass fibre reinforced aluminium honeycomb sandwiches(SAGE Publications Ltd, 2018) Crupi, Vincenzo; Kara, Emre; Epasto, Gabriella; Guglielmino, Eugenio; Aykul, HalilHoneycomb sandwich structures are increasingly used in the automotive, aerospace and shipbuilding industries where fuel savings, increase in load carrying capacity, vehicle safety and decrease in gas emissions are very important aspects. The aim of this study was to develop the theoretical methods, initially proposed by the authors and by other researchers for the prediction of low-velocity impact responses of sandwich structures. The developed methods were applied to sandwich structures with aluminium honeycomb cores and glass-epoxy facings for the assessment of impact parameters and for the prediction of limit loads. The values of model parameters were compared with data reported in literature and the predictions of the limit loads were validated by means of the experimental data. Good achievement was obtained between the results of the theoretical models and the experimental data. The failure mode and the internal damage of the sandwich panels have been investigated using 3D computed tomography, which allowed the evaluation of parameters of energy balance model, and infrared thermography, which allowed the detection of the temperature evolution of the specimens during the tests. The experimental and theoretical results demonstrated that the use of glass-epoxy reinforcement on aluminium honeycomb sandwiches enhances the energy absorption and load carrying capacities. © 2016, © The Author(s) 2016.
