Research on Engineering Structures and Materials

293-313

Authors: Ahmet Meram, Betül Sözen

This paper investigates the manufacturing variants influential on the strength of 3D printed products. In contrast to the traditional manufacturing methods which produce the final product via removing materials from parts, in 3D printing technology the products are provided with adding layer by layer directly from a digital file. 3D printing technology due to overcoming the many difficulties and limitations of conventional fabrication approaches is a rapidly progressing technology which takes attention in many industries such as aerospace, automotive, medical and building industries. This paper aims to research the variants affecting the mechanical properties of components produced by 3D printing technologies. To reach this aim a comprehensive review was conducted to determine the various process and geometric parameters in 3D printing technologies. The conducted literature survey results indicate that besides the filament material, the nozzle speed and diameter, layer thickness, filament diameter, printing raster angle, printing pattern, temperature and infill density are parameters which influence the final product quality and mechanical properties in term of ultimate tensile strength, yield stress and elasticity modulus. It is concluded that 3D printing filament materials strength has direct affect on the strength of final product. By providing the adequate thermal behavior of the system, the cohesion between layers can be improved. Extrusion speed affects surface roughness and quality of the produced components. Nozzle diameter has a significant influence on interlayer cohesion. The honeycomb pattern due to facilitating the load transfer between layers provides higher mechanical strength. Findings of this study will guide the researchers and manufacturers to select appropriate printing parameters to produce component with optimum mechanical properties.

327-350

Authors: Aykut Elmas, Güliz Akyüz, Ayhan Bergal, Müberra Andaç, Ömer Andaç

Mathematical models of the drug release have been used in the drug delivery (DD) field for more than 50 years by the scientists in the drug development process. These models not only help scientists to learn the dynamics of the drugs release, but also help them to save money and time by helping to design more effective experiments. There is no model in the literature that covers all drug release scenarios. Also, some system-specific models have complex mathematical equations and these models are not suitable for general use. Zero Order Model, First Order Model, Higuchi Model, Peppas Model and Hixon Crowell Model are used in 85% of drug release studies in total. The popularity of these models comes from their simplicity, easy mathematical expressions and implementation. In this review, mathematical derivations of these five models are shown in detail. The points to be considered during the derivation and the problems that may be encountered are carefully explained along with their solutions. In addition, the application of the models to drug release data and the points to be considered were obtained by writing from the scratch without using any ready software while obtaining the fit function. In this way, many problems are better understood, and their solutions are explained. Finally, the obtained fit functions are interpreted.

363-374

Authors: Canan Kandilli, Mert Uzel

Photovoltaic thermal systems (PVT) produces both electricity and thermal energy by the same module. However, solar energy exhibits non-continuous character, and causes some problems for obtaining stabile energy due to its unsteady regime. Thermal energy storage systems could be employed as a solution the mentioned problems. There are no studies in the literature regarding evaluation of the annual performance of PVT systems integrated with natural zeolites. It is the motivation behind of the present study. Natural zeolites could be utilized for thermal storage and management with PVT systems. In this study, it is aimed to performed annual performance of the PVT system integrated with natural zeolite as a thermal storage material to manage the excessive heat on PV. Average overall energy efficiency values were found as 0.56; 0.54; 0.49; 0.49; 0.48; 0.46; 0.45; 0.46; 0.50; 0.53; 0.54 and 0.56 from January to December, respectively. Annual total overall energy produced by the PVT system integrated with natural zeolite was found as 1294.88 kWh/year per module. Annual saving per module is reached as 117.83 € per module. With the acceptance of the system cost of 942.8 €, simple payback period is approximately 8 years. This payback time, which is found on a single module, will surely decrease at higher installed powers.

385-409

Authors: Abdullah Fettahoglu, Mehmet Cemal Genes

Deformation of most pavements is practically inelastic. Thus, the exact calculation of pavement deformation often requires use of a damage evaluation law to characterize the stress-strain relationship mathematically. Asphalt, polymer, and reinforced concrete are all examples of such pavements. However, concrete pavements without reinforcement are generally assumed to behave linear elastic. Concrete pavements without reinforcement are used sometimes as permanent pavements with dowels such as airport apron pavement, but sometimes they are used as temporary pavements during the mobilization or initial phases of new construction projects as well. When used as permanent pavements, their design is performed similar to rigid pavements, which has international acceptance by highway engineers, or by finite element analysis. When used as temporary works during the mobilization phase, or when a road is urgently required on a construction site, their design is often problematic, because advanced highway design or finite element analysis might be momently unavailable. A rapid, conservative, and reliable hand calculation method for temporary concrete pavements without reinforcement is therefore required. In this study, design charts are provided to allow hand calculations of temporary concrete pavements. In addition, a numerical example is solved to illustrate the use of derived charts. The effects of certain parameters on the stress behavior of concrete pavements are also investigated.

425-437

Authors: Marjo Hysenlliu, Altin Bidaj, Huseyin Bilgin

Recent earthquakes occurred in many parts of the world have shown that unreinforced masonry [URM] buildings constructed according to older codes may constitute an important source of risk. It is known that the mechanical response of the masonry structures depends on several factors including the compressive and shear strength of its constituents, bricks shape as well as the volumetric ratio between the wall texture and components. In this study, the effects of the material choices of a particular type of masonry buildings were studied. The typology chosen in this study represents a typified masonry building of the current Albanian building stock; these buildings were mostly built between 1977-78 and thus were designed without considering the seismic requirements proposed in today’s modern codes. This template building has been constructed in different regions of the country with the same architectural and structural configuration in two versions; red clay bricks and silicate bricks. The aim of this study is to investigate the influence of these two different materials on the seismic response of the selected masonry building. The evaluation is based on the use of nonlinear static analyses, performed by using TREMURI software. In order to estimate the reliable seismic response for this typology, extensive research in terms of historical information, structural characterization and the definition of the inherent material parameters has been executed. Upon the evaluation of the obtained results, in contrast to the type of buildings constructed by clay masonry, calcium silicate one showed a stiffer and slightly stronger response. However, at similar values of in-plane, lateral drift they exhibited more brittle response yielding unforeseen damage during seismic excitations.

197-206

Authors: Melik Ziya Yakut, Sinem Esen

In this study; based on energy-efficient design parameters, the effects of building design parameters on the energy consumption of the building were examined. Accordingly, a reference building has been created as an example of application in the hot-humid climate zone. In the process of modelling the building, BIM (Building Information Modelling) software Autodesk Revit was used. The model has been transferred to Green Building Studio (GBS) for energy performance analysis and evaluation of design alternatives. The parameters evaluated in terms of energy consumption of the building were selected from among the design alternatives produced by GBS, based on energy-efficient design parameters. As a result of the energy performance analysis of the reference building via GBS, the building's annual electricity consumption is 35,137 kWh and the annual fuel consumption is 93,729 MJ. Based on the evaluation of selected design parameters as a result of reference building energy performance analysis; HVAC systems have been found to have the most impact on energy consumption (rates of changes; 36.83% in annual electricity consumption, 90.27% in annual fuel consumption). HVAC systems, selected to be highly efficient and suitable for climate type, have the potential to save significant energy in the amount of energy consumption throughout the life cycle. In addition to this, as of the early design phase, the energy efficient design of the building is of great importance in terms of a holistic evaluation and maximum energy efficiency.

229-240

Authors: Hayri Baytan Ozmen, Mehmet Inel, Yunus Demirtas

Soft story irregularity is one of the main reasons of the building damage during past earthquakes and has been mentioned in almost all reconnaissance reports. Soft story due to increased story height is a recognized subject but soft story may also arise due to abrupt changes in amount of infill walls between stories, which are usually not considered as a part of load bearing system. This study investigates soft story behavior due to increased story height, lack of load bearing infill walls at ground story and existence of both cases using nonlinear static and dynamic response history analyses. Mid-rise reinforced concrete buildings are considered due to their high portion in existing building stock. Displacement capacities at Immediate Occupancy, Life Safety and Collapse Prevention performance levels and story drift demands of the regular and soft story models are determined. Soft story behavior due to change in story height and/or infill amount is evaluated in view of displacement capacities, drift demands and structural behavior. It is observed that, soft story due to infill walls may be as damaging as soft story due to increased story height.

257-269

Authors: Fatoş Koç, Selay Sert Çok, Nilay Gizli

In this study, silica aerogels were produced by two-step sol-gel method to investigate the effect of pH on the physical, chemical and textural structure of aerogels. Tetraethyl orthosilicate (TEOS) used as a silica source. (3-aminopropyl) triethoxysilane (APTES) acted as a silica co-precursor. The quantity of sol precursors kept constant through the experiments and the pH of hydrolysis and condensation reactions were varied. As a result of the experimental studies, the optimum pH values to achieve monolithic aerogel were obtained when the pH of hydrolysis is 3 and the pH of condensation is 10. Physical, chemical and morphological characteristics of the samples were examined by performing FTIR and SEM and density analyses. Results showed that the sample SG-pH3/7 had also well-defined porous structure with homogenous pore distribution, a stable lightweight and monolithic form.

283-292

Authors: Ekrem Altuncu, Recep Akyüz

Automobile brake disc are subjected to cyclic thermal, mechanical and corrosive effects. In general, gray cast iron grades are preferred as disc brake materials. Lamellar cast iron disc brakes have a limited lifetime and are replaced periodically during the maintenance-service process. With the growing interest in the number of Battery Electric Vehicles (BEV), there is a need for disc brake with longer service life on discs. Therefore, in the automotive sector, in line with increasing competition and user demands, there is an interest in new coating types and materials with corrosion free properties, a longer service life and high brake performance. Wear and corrosion resistant plasma spray coatings are the key to increasing the service life and braking performance of cast iron discs. In this study, the discs (GG20) are coated with Alumina- Titania based ceramic material by atmospheric plasma spray method. The ceramic coated disc brakes were installed on the road driving test vehicle and disc brake thickness reduction were measured periodically according to wear test plan throughout 20.000 km. The test results show that the ceramic coating provides 18 times more wear resistance compared to uncoated disc brake. In addition, coated disc brakes exhibited superior performance in corrosion tests. As a result of the investigations carried out on disc brakes, it is understood that plasma spray ceramic coatings can be used alternatively in brake disc systems.

105-118

Authors: Mehmet Palanci

Main components such as columns and beams of reinforced concrete (RC) buildings are constructed as symmetrically and unsymmetrically reinforced. Symmetrically reinforced concrete members are widely studied and some analytical/numerical approaches are provided. However, unsymmetrically reinforced concrete members are not adequately investigated and further research is required to predict response of these members. For this reason, this study focuses on strength and deformation capacity prediction of unsymmetrically RC members at yield which primarily required for the design and assessment. In the study, wide range of RC sections are generated and analyzed using different section dimensions, material types, reinforcement ratios and configurations to reveal behavior of these members. Influence of parameters on the responses is investigated and they are contributed to prediction equations by statistical evaluations. Prediction equations are first tested with analytical RC section results and comparisons have shown very good agreement. Equations are then applied to predict dynamic features of two experimental MDOF buildings. Evaluations have revealed the reliability of prediction equations in approximation of responses in building scale.

127-140

Authors: Sevim Alisir, Sinem Cevik

Many studies are being carried out on factors such as casting temperature, cooling rate, mold design and, so on due to the effects of casting and solidification conditions on the mechanical properties of the final product. However, given literature, there appears to be no comprehensive study on the effect of casting mold sand components on the mechanical properties of cast iron. From this point of view within the scope of this study, the effects of casting mold sand and binder on the cast iron were investigated. By using silica and olivine as foundry sand at different ratios, bentonite and perlite as binders, the effects of them on the microstructure and the mechanical properties of casting were investigated. The microstructures of the products show that as the cooling rate slows down, the distribution of graphite particles in the structure changes from flakes to nodules. These structural changes are very matched with the results of mechanical properties. Therefore, when the cooling rate decreases, the hardness decreases from 310 HV to 239 HV in all of the groups. Also, the bending strength is going from 971.53 MPa to 487.42 MPa, like in the hardness results. On the contrary, the deformation increases from 13 % to 24 % when cooling rates decreases. This study clearly demonstrates that the products can be obtained by changing the heat conduction coefficient of the casting mold with different mechanical properties from the same molten metal.

153-165

Authors: Hatice Aylin Karahan Toprakci, Ayse Turgut, Ozan Toprakci

In this study, highly flexible polymer nanocomposites that can be stretched more than 9 times their original length were successfully fabricated by using poly [styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) and vapor grown carbon nanofibers (VGCNFs). Two different polymers were used in order to investigate the effects of the polymer molecular weight on viscosity, morphological and mechanical properties of the samples. Mixing was carried out by a planetary high shear mixer for various levels of VGCNFs and SEBS. Nanocomposites were prepared by the combination of solvent casting and compression molding. Viscosity measurements were carried out as a function of filler ratio for both polymers. Higher molecular weight and higher filler ratio led to higher viscosity. Morphological analysis showed homogeneous filler dispersion without any dominant filler orientation throughout the composites with good filler-matrix interface and absence of any pores or voids. Filler content and matrix molecular weight were found significant for mechanical properties. The mechanical strength and elastic modulus of the nanocomposites increased by the addition of VGCNF regardless of the polymer molecular weight. Nanocomposites fabricated by using higher molecular weight polymer showed better mechanical properties. Above mentioned attributes those belong to both polymer composites meet the requirements of flexible electronics and can be used for many applications including micro-electro-mechanical systems, conductive coatings, electromagnetic shielding applications, polymeric sensors and actuators.

183-195

Authors: Ahsen Ünal, Işıl Özer, Melek Erol Taygun, Sadriye Küçükbayrak

Composites developed by combining bioactive glasses and biopolymers are attractive materials for use in bone tissue engineering scaffolds due to their bioactivity, biocompatibility, osteoconductivity and mechanical properties. From this point of view, in this study, three-dimensional polymer/bioactive composite scaffolds were fabricated by using polymer foam replication method. To be able to achieve this goal, in the first stage new bioactive glass composition in the system SiO2-CaO-Na2O-P2O5 were developed with the incorporation of copper which have antibacterial and angiogenic properties. Scaffolds that mimic the structure of the foams were obtained after the heat treatment process. Then, the scaffolds were coated with gelatine at different percentages (1 and 3 weight%) in order to improve mechanical properties of the scaffolds. Microstructural, physical, chemical and mechanical properties of the composite scaffolds were investigated by using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), compressive strength test and porosity measurements. Furthermore, bioactivity and biodegradability behavior of the samples were determined by in vitro simulated body fluid (SBF) studies. The results showed that all scaffolds favored precipitation of calcium phosphate layer when they were soaked in SBF; they can also deliver controlled doses of copper toward the SBF medium. It was concluded that scaffolds coated with gelatine may be promising candidates for bone tissue engineering applications due to their porosity, bioactivity and appropriate biodegradation rate.

1-21

Authors: Berrin İkizler

Antireflective (AR) SiO2 coatings were developed in this work to increase the transmittance of glass in the visible light range of 400-800 nm, due to their potential applications on solar energy systems. Also, double-layer AR coatings were prepared by covering AR SiO2 layer with a dense TiO2 layer with the aim of protecting AR layer from environmental effects. SiO2 coatings were obtained with sol-gel and dip coating methods, by using acid- and base-catalyzed silica sols as precursors. Only 1% transmittance increase was gained with acid- catalyzed SiO2 coating due to its dense structure. On the contrary, SiO2 coatings formed by base-catalyzed sol have transmittance > 99% in the 460-660 nm range and of 99.8% at 550 nm, corresponding to the wavelength at maximum intensity of solar spectrum. This high values were attributed to the porous structure of the film revealed by SEM and AFM analysis, and to the optimized thickness of coating achieved at 90-120 mm/min withdrawal speeds. Transmittance of base-catalyzed SiO2 coatings decreased to an average value of 96.2% after coated with high refractive index TiO2 layer. However, still a 5-6% achievement in transmittance of glass in 400-800 nm range was attained by optimizing the thickness of each layer using different withdrawal speeds, and concentration and types of the precursor sols. Characterization of the coatings was performed with SEM, AFM, EDS and FTIR analysis.

35-44

Authors: Samiul Kaiser, Mohammad Salim Kaiser

The wear behaviour of the wood and knot of pine timber is evaluated at ambient conditions. The experiment is carried out under dry sliding conditions using a pin-on-disc apparatus. Wear testing parameters are chosen as 20N load, sliding velocity of 0.64 ms -1 and sliding distance ranging from 200m-4500m. The worn surfaces are characterized by optical microscope and scanning electron microscopy. Hardness of wood and knot samples is measured in Durometer hardness tester, tensile testing by an Instron testing machine and density of the samples is calculate from the data of volume and weight. The results of the wear test reveal that the knot shows the better wear properties due to higher strength and density. SEM study of the knot and wood disclose that the knot contents compact cell wall than that of wood.

53-62

Authors: Özgür Demircan

Glass fiber/epoxy resin/multi-walled carbon nanotubes (MWCNTs) were used to fabricate the nano materials integrated thermoset composite materials in this study. Thermoset composites with and without nano materials were fabricated using resin transfer molding (RTM) methods. The fabricated samples were tested with compression after impact and charpy impact tests. The samples with MWCNTs demonstrated the best improvement of the compression after impact modulus and strength with 31% and 5.6% compared to the samples without carbon nanotubes. The nano materials integrated specimens showed 10.2% improvement of charpy impact strength against specimens without carbon nanotubes in 90° degree direction. Due to the existing of the carbon nanotubes between fiber and polymer matrix was the reason of the improvement of the mechanical properties of carbon nanotubes integrated composites.

75-84

Authors: Uğur Çavdar, Oner Haşim Olgun

Because of their exceptional features, advanced composites with polymer matrix attract increasing interest in engineering applications recently. Compared to their weight ratio due to the high endurance and hardness values applications of polymer matrixed composites of lightweight, low density, and high performance are popular in military and civil aerospace, automotive, wind power and many other industries. Nowadays, induction heating of the carbon fiber reinforced thermoplastic composites is one of the most important worldwide studies. Due to the importance of accelerating the rate of production from approximately 180-240 minutes to a few minutes, in this study, the weldability of the carbon fiber reinforced thermoplastic composites was investigated.

97-104

Authors: Mehmet Topuz, Burak Dikici

Crowns are materials that attracting the attention and lithium disilicates among them widely used because of their high bulk mechanical features. Increasing the bioactivity of crowns has generally been a common aspect of all studies. In this study, lithium disilicate dental blocks were coated with bioactive calcium– phosphate components using sol–gel dip–coating methods to increase their surface bioactivity. Two coating methods called as slurry and powder methods were proposed to obtain dense and remarkable layer on the lithium disilicate substrates. The coating layers were characterized by scanning electron microscopy attached with energy dispersive spectroscopy. Coating procedures have successfully accomplished and show enhanced surface properties with terms of calcium/phosphate ratios. Tri–calcium phosphate obtained by the slurry method, which has 1.5 calcium/phosphate ratio, is a favorable structure for bio–absorbable. However, the powder method has approximately 1.67 calcium/phosphate ratio which necessary for hydroxyapatite (HA) structure for higher crystallinity and lower solubility properties.