Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Conference Object Asymmetry in the Tension and Compression Flow Stress and the Effect of Sub-Cell Size on the Hardness of a Selective Laser Melt 316l Stainless Steel(Springer, 2022) Güden, Mustafa; Enser, Samed; Arslan Hamat, Burcu; Tanrıkulu, A. Alptuğ; Yavaş, HakanAn asymmetry between tension and compression tests was determined experimentally in the Selective Laser Melt (SLM) stainless steel 316L alloy in the building direction. The asymmetry was ascribed to the used biaxial scanning strategy which resulted in a strong alignment of 〈110〉 along the build direction (fiber texture) and a random distribution of 〈100〉, 〈110〉 and 〈111〉 directions normal to the building direction. The strong fiber texture in the building direction induced lower twinning stress in tension than in compression, while the tension and compression twining stresses were found similar in the normal to building direction. The favored twinning in the specimens tested in the building direction resulted in a higher tensile true fracture strain; hence, a higher ductility. Lastly, the hardness measurements made on the specimens having similar gain sizes, but different sub-cell sizes processed using higher and lower laser powers tended to support that the sub-cell boundaries in SLM-316L alloy acted as imperfect barriers to the dislocation motion.Article An Experimental and Comparative Study of the Self-Loosening of Bolted-Joints Under Cyclic Transverse Loading(Sakarya University, 2021) İnce, U.; Güden, M.The capabilities of analytic models in predicting the experimental critical displacements of the self-loosening of bolted-joints were investigated experimentally and numerically. The experimental loosening rates were determined in a Junker test bench at a constant transverse displacement amplitude (0.45 mm) and under varying initial clamp force and clamp length and controlled bearing and thread friction coefficients. The analytic critical displacements were then calculated using experimental parameters. In addition, a three-dimensional accompanying finite element (FE) model was developed in order to calculate the ratio of spring constants engaging the thread to spring. The results showed relatively low capabilities of present analytic model in the prediction of the critical displacements of the self-loosening of bolted-joints. The efforts to modify the nut reaction moment and the inclination compliance of bolt head portion in the investigated equations however resulted moderate increase in the appropriate predictions. On the other side, the use of the reaction moment determined by FE model increased the appropriate prediction from 58.3 to 73.4%. The accuracy of the equations was further increased by the use of an appropriate kw value, but the increase in this case was only ~4%. © 2021, Sakarya University. All rights reserved.Conference Object Projectile Impact Testing Aluminum Corrugated Core Composite Sandwiches Using Aluminum Corrugated Projectiles: Experimental and Numerical Investigation(Trans Tech Publications, 2017) Odacı, İsmet Kutlay; Kılıçaslan, Cenk; Taşdemirci, Alper; Mamalis, Athanasios G.; Güden, MustafaE-glass/polyester composite plates and 1050 H14 aluminum trapezoidal corrugated core composite sandwich plates were projectile impact tested using 1050 H14 aluminum trapezoidal fin corrugated projectiles with and without face sheets. The projectile impact tests were simulated in LS-DYNA. The MAT_162 material model parameters of the composite were determined and then optimized by the quasi-static and high strain rate tests. Non-centered projectile impact test models were validated by the experimental and numerical back face displacements of the impacted plates. Then, the centered projectile impact test models were developed and the resultant plate displacements were compared with those of the TNT mass equal Conwep simulations. The projectiles with face sheets induced similar displacement with the Conwep blast simulation, while the projectiles without face sheets underestimated the Conwep displacements, which was attributed to more uniform pressure distribution with the use of the face sheets on the test plates. © 2018 Trans Tech Publications, Switzerland.Conference Object The Shape and Size Effect of the Diatom Frustule Addition on the Compression Behavior of an Epoxy(Trans Tech Publications, 2018) Zeren, Doğuş; Kesici, Kutsal; Sukatar, Atakan; Güden, MustafaThe effects of the Achnanthes Taeniata and the diatomaceous earth (diatomite) frustules addition on the compressive strength of an epoxy matrix were investigated experimentally. The Achnanthes Taeniata frustules having relatively high length/diameter aspect ratio (2-4) were isolated and cultured in laboratory. While the as-received commercial natural diatomite frustules were non-homogenous in shape and size. The filling epoxy matrix with ~6 wt% of commercial natural diatomite increased the compressive strength from 60 MPa to 67 MPa, while the Achnanthes Taeniata frustules addition increased to 79 MPa. The increased compressive strength and modulus of the the Achnanthes Taeniata frustules filled epoxy was attributed to the higher aspect ratio and relatively strong bonding with the epoxy matrix. The more effective load transfer from the matrix to the Achnanthes Taeniata frustules associated with the enhanced interface bonding was also proved microscopically. The frustules were observed to pull-out on the fracture surface of the Achnanthes Taeniata frustules filled epoxy.Conference Object Citation - WoS: 8Citation - Scopus: 12Mechanical Properties of Hydroxyapatite Composites Reinforced With Hydroxyapatite Whiskers(Trans Tech Publications, 2004) Şimşek, Deniz; Çiftçioğlu, Rukiye; Güden, Mustafa; Çiftçioğlu, Muhsin; Harsa, Hayriye ŞebnemSintering and mechanical behavior of pure and hydroxyapatite (HA) whisker reinforced HA composites were investigated in this work. Pure and composite samples were prepared by using a commercial powder and whiskers prepared by molten salt synthesis. The dry-pressed samples were sintered in the 800 and 1300°C range. The effect of whisker-addition on the mechanical properties of HA was investigated through compression and hardness testing. Compressive strength and fracture strain were observed to increase by the addition of whiskers.Conference Object Citation - WoS: 5Citation - Scopus: 5Preparation and Microstuructural Development of Nanocrystalline Titania and Alumina(Trans Tech Publications, 2004) Çağlar Duvarcı, Özlem; Çiftçioğlu, Muhsin; Güden, Mustafa; Arıkut, G.The preparation of nanocrystalline titania and alumina was investigated by sol-gel methods using titanium isopropoxide, boehmite and aluminum isopropoxide. Various drying control chemical additives like oxalic acid, acetic acid and polyacrylic acid were used for modifying the drying behaviour and shrinkage of the gels. The sintered densities of the ceramics prepared by sol-gel processing and the dried gels were in the 79-99% of theoretical density for rutile. The green and sintered densities of the pellets prepared by uniaxial pressing of powders derived from sols, gels and precipitation techniques for titania were in the 40-52% and 55-83% respectively. The titania ceramics were observed to experience anatase-rutile phase transformation upon heat treatment at 650oC. The grain size of the sintered ceramics at 650oC was determined to be about 26 nm. Grain size of titania increased to 213 nm. at 850oC. The mechanical properties of these nanocrystalline ceramics were investigated by using microhardness testing.Article Citation - WoS: 20Citation - Scopus: 22Photocatalytic Antimicrobial Effect of Tio2 Anatase Thin-Film–coated Orthodontic Arch Wires on 3 Oral Pathogens(TUBITAK, 2014) Özyıldız, Figen; Uzel, Ataç; Hazar, Ayşe Serpil; Güden, Mustafa; Ölmez, Sultan; Aras, Işıl; Karaboz, İsmailThe aim of this study was to introduce antimicrobial activity to stainless steel orthodontic arch wires by coating them with TiO2 in anatase form. Stainless steel (0.016 × 0.022 inch), D-rect (0.016 × 0.022 inch), and multistranded hammered retainer wires (0.014 × 0.018 inch) were coated with TiO2 anatase by the sol-gel dip coating method. The wires were assessed for their photocatalytic antimicrobial activity against Streptococcus mutans, Candida albicans, and Enterococcus faecalis. After illumination under UVA (315– 400 nm) at 1.0 mW/cm2 for 1 h, the reduction efficiencies of the anatase-coated arch wires were calculated by using colony-forming unit counts. All anatase-coated arch wires showed remarkable inhibitor effects against the test microorganisms under UVA. The most efficient wire on S. mutans was the stainless steel wire, with a 99.99% reduction in growth, but multistranded hammered retainer wire was the most active against both C. albicans and E. faecalis, with 98.0% and 91.68% reduction rates, respectively. TiO2-coated arch wires exposed to UVA illumination showed significant antimicrobial activity when compared with uncoated samples and coated, but not UVA-exposed, samples. Our results suggest that the antimicrobial effect of TiO2-coated arch wires in long-lasting orthodontic treatments would be beneficial for the prophylaxis of caries.Article Citation - WoS: 12Citation - Scopus: 15Morphological and Molecular Identification of Pennate Diatoms Isolated From Urla, Izmir, Coast of the Aegean Sea(TUBITAK, 2013) Kesici, Kutsal; Tüney, İnci; Sukatar, Atakan; Zeren, Doğuş; Güden, MustafaDiatoms represent an important class of aquatic phototrophs. They are not only one of the major contributors to global carbon fixation, but also play a key role in the biogeochemical cycling of silica. Molecular identification methods based on conserved DNA sequences, such as ITS (Internal Transcribed Spacer) have revolutionized our knowledge and understanding of conventional taxonomy. In this study, we aimed to compare the conventional identification methods with molecular identification methods. To do so, we isolated four diatom samples from Coast of Urla and characterized them using light microscopy (LM) and scanning electron microscopy (SEM) according to morphological features. Then, we amplified ITS regions using conventional polymerase chain reaction (PCR), sequenced the PCR products and analyzed the sequences using bioinformatic tools. Bioinformatic analysis indicated that the isolated species had high sequence similarity to Pseudo-nitzschia sp., Achnanthes sp., Amphora sp. and Cylindrotheca sp. We believe that molecular identification methods enable rapid and more reliable identification of diatom species and are crucial for monitoring harmful algal blooms.