Research on Engineering Structures and Materials

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.