Publications without Fulltext
Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
Browse
6 results
Search Results
Publication Metadata only Dimensional stability of 51CrV4 steel during bainitic phase transformation under tensile and compressive stresses(Elsevier, 2010) Lambers H.-G.; Maier H.J.; Department of Mechanical Engineering; Canadinç, Demircan; Faculty Member; Department of Mechanical Engineering; College of Engineering; 23433The effect of the prior austenitization treatment on the stress-strain response of a low alloy 51CrV4 steel in its supercooled austenitic state and its effect on the evolution of transformation plasticity strain during a subsequent isothermal bainitic transformation was investigated. One of the key findings is that the prior austenitization treatment strongly affects the evolution of transformation plasticity strains during the subsequent isothermal bainitic transformation under stress, such that higher transformation plasticity strains are present when the austenite grain size is increased. In addition, higher 0.2% offset yield strengths of the supercooled austenite are present following an incomplete austenitization treatment due to the existence of residual carbides. Overall, the current results clearly lay out the effect of the prior austenitization treatment on the stress-strain response of the supercooled austenite and the evolution of transformation plasticity during bainitic transformation.Publication Metadata only On the cyclic stability and fatigue performance of ultrafine-grained interstitial-free steel under mean stress(Trans Tech Publications Ltd, 2008) Niendorf, Thomas; Maier, Hans J.; Karaman, Ibrahim; Department of Mechanical Engineering; Canadinç, Demircan; Faculty Member; Department of Mechanical Engineering; College of Engineering; 23433This paper reports on the fatigue performance of an ultrafine-grained (UFG) interstitial-free (IF) steel deformed at various mean stress levels. The UFG microstructure was achieved using equal channel angular extrusion processing at room temperature (RT) and along an "efficient" route, giving way to the formation of high angle grain boundaries (HAGBs) with a high volume fraction. The current study not only confirms the previous finding that a high volume fraction of HAGBs promotes cyclic stability, but also inquires into the role of mean stress level on the cyclic stability. It is shown that the UFG IF steel exhibits a stable cyclic deformation response in the lowcycle fatigue regime within the medium applied mean stress range of -75 to 75 MPa. The corresponding fatigue lives can still be predicted with the Smith-Watson-Topper approach within this range. Furthermore, the present study demonstrates that the evolution of mean strains with cyclic deformation can be linked to the evolution of mean stresses in strain-controlled loading.Publication Metadata only Discrete and continuous mathematical models for torsional vibration of micromechanical scanners(Springer, 2007) Department of Electrical and Electronics Engineering; N/A; Ürey, Hakan; Faculty Member; N/A; Department of Electrical and Electronics Engineering; College of Engineering; N/A; 8579; N/AMicromechanical scanners are used in various industrial scanning applications like. display and imaging technologies. The desired vibration mode is often the torsional mode, so derivation of an accurate mathematical model for calculation of torsional mode frequency has great importance. In this work, discrete and continuous mathematical models are given for free torsional vibration of a box shaped scanner suspended with two beams. Numerical calculation of torsional rigidity using energy methods is shown. The derivations are extendible to scanners that have non-rectangular beam cross-sections, orthotropic material anisotropy, and different mirror geometries. Analytical formulas are compared with three-dimensional FEM simulations using ANSYS commercial software. The FEM simulations and analytical formulas are verified with experimental results. FEM simulations and experimental results showed that simple discrete models can be used for a wide range of beam dimensions except for the cases where beam inertia is comparable to mirror inertia.Publication Metadata only An analytical model for engagement regions in machining of 3-d free-form surfaces(Japan Society of Mechanical Engineers (JSME), 2005) N/A; Department of Mechanical Engineering; N/A; Lazoğlu, İsmail; Öztürk, Burak; Faculty Member; Master Student; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); College of Engineering; Graduate School of Sciences and Engineering; 179391; N/AIn the machining simulations of 3D free-form surfaces with ball-end-mill process, determinations of instantaneously changing tool-workpiece contact regions and chip load play very critical roles in forces and surface quality predictions. Cutting force models for ball-end milling are based on the undeformed chip thickness. Undeformed chip thicknesses can be constructed from the boundaries of instantaneous contact region between the ball-end mill and workpiece. In order to predict the cutting forces accurately, determination of the varying contact region is important. In the literature, there are two main contact region constructing methods; one is the Z-mapping and the other one is using solid modeler based Boolean operation method. Both methods construct the contact region within accuracy limits but the computational time for these methods are long such that it is not possible to calculate the forces at the same time of (CL) points construction. This paper presents development of a new analytical method for the determination of the instantaneous contact regions and chip load in the 3-D machining of monotonic free-form surfaces.Publication Metadata only Friction and wear behaviors of tin coatings under dry and vacuum conditions(Taylor & Francis Inc, 2019) Kara, Levent; Özkan, Doğuş; Sulukan, Egemen; Sert, Yaşar; Sert, Tugay Sonsuz; N/A; Yağcı, Mustafa Barış; Researcher; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/AIn this study, pure TiN coatings were applied on AISI 52100 steel surfaces with a magnetron sputterer at different direct current (DC) powers and N-2 flows to develop a wear-resistant coating for sliding tribopairs working in atmospheric and vacuum conditions. Wear and friction characteristics of these coatings were investigated with a tribometer under both vacuum and atmospheric conditions. DC power and N-2 flow affected the coating thickness and structure. TiN coatings showed different wear and friction characteristics under ambient and vacuum conditions due to the oxidation level of the surface.Publication Metadata only A novel hybrid frost detection and defrosting system for domestic refrigerators(Elsevier, 2020) N/A; N/A; N/A; Department of Mechanical Engineering; Malik, Anjum Naeem; Khan, Shaheryar Atta; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179391The frosting is a phenomenon most detrimental to the efficiency of refrigeration systems. The accumulation of frost blocks the airflow, deteriorating the cooling capacity and the coefficient of performance. The commercially available refrigeration systems use a blind and periodic defrosting cycle without any quantification of frost, which leads to lower efficiencies. Considering the new and tougher energy regulations in the refrigerators, nowadays increasing the efficiencies of the refrigerators becomes more critical. In this article, a new hybrid frost detection - defrosting system (HFDDS) is proposed that comprises of a novel photo-capacitive sensing technique and a dual-purpose additively manufacturable sensor and defrosting heater. The HFDDS can detect the formation of frost, measures the thickness of frost from 1.3 to 8 mm with a 5% margin of error, and triggers a defrosting response once a critical frost thickness is attained. The HFDDS is targeted to provide a defrosting on-demand instead of the inefficient blind and periodic defrosting cycles.