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.