Makine Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/263
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Article Citation - Scopus: 3Numerical Simulation and Experimental Investigation: Metal Spinning Process of Stepped Thin-Walled Cylindrical Workpiece(Murat Yakar, 2022) Seyedzavvar, M.; Akar, S.; Abbasi, H.Many equipment and devices utilized in the aerospace industry are formed as symmetric parts through high plastic deformation of high strength sheet metal alloys with low thickness. Considering the inherent advantages of the spinning process of simple tooling and concentrated deformation loading, this process can be considered as one of the main options in producing these thin-sectioned lightweight parts. In this study, a Finite Element (FE) model has been developed to simulate the formation of a stepped thin-walled cylindrical workpiece of AISI 316 stainless steel alloy by spinning process. The FE simulation results were employed to investigate the effects of process parameters, including feed rate of the roller and rotational velocity of the mandrel on the distribution of stress and strain in the sheet metal, wrinkling failure, and thinning of the sheet metal during deformation. Experiments were carried out using selective input parameters based on the results of FE simulations. The comparison between FE simulations and experiments revealed that the developed model could predict the thinning of the sheet metals with over 93 % accuracy. Additionally, a good agreement between the experimentally deformed sheet configurations with those resulting from finite element simulations has been observed. © Author(s) 2022.Article Citation - WoS: 4Citation - Scopus: 7Enhanced Gradient Crystal-Plasticity Study of Size Effects in a Β-Titanium Alloy(Iop Publishing Ltd, 2017) Nowag, Kai; Roy, Anish; Ghisleni, Rudy; Michler, Johann; Silberschmidt, Vadim V.; Demiral, MuratA calibrated model of enhanced strain-gradient crystal plasticity is proposed, which is shown to characterize adequate deformation behaviour of bcc single crystals of a beta-Ti alloy (Ti-15-3-3-3). In this model, in addition to strain gradients evolving in the course of deformation, incipient strain gradients, related to a component's surface-to-volume ratio, is accounted for. Predictive capabilities of the model in characterizing a size effect in an initial yield and a work-hardening rate in small-scale components is demonstrated. The characteristic length-scale, i.e. the component's dimensions below which the size effect is observed, was found to depend on densities of polar and statistical dislocations and interaction between them.Article Citation - WoS: 33Citation - Scopus: 38Void Growth in High Strength Aluminium Alloy Single Crystals: a Cpfem Based Study(Iop Publishing Ltd, 2017) Siddiq, M. Amir; Demiral, Murat; Asim, UmairHigh strength aluminium alloys that are produced through forming and joining processes are widely used in aerospace components. The ductile failure in these metals occurs due to the evolution and accumulation of microscopic defects, such as microvoids and shear bands. The present work investigates the underlying physical mechanisms during ductile failure by performing a rigorous, fully-validated, three-dimensional crystal plasticity, finite element study with aluminium alloy single crystals. Representative volume element (RVE) based simulations of single crystalline aluminium alloys (AA-5xxx) with different void geometries and orientations have been performed. Both local and nonlocal crystal plasticity constitutive models have been implemented in a finite element framework and are used to seek new insights into the interrelationships among void growth, initial porosity, initial void size, plastic anisotropy, and local/nonlocal size effects.Article Citation - WoS: 36Citation - Scopus: 42Improvement of Electric Discharge Machining (Edm) Performance of Ti-6al Alloy With Added Graphite Powder To Dielectric(Assoc Mechanical Engineers Technicians Slovenia, 2015) Cogun, Can; Unses, EmreTi-6Al-4V is a well-known Ti alloy widely used in the aerospace industry and belongs to the group of difficult-to-machine materials. It is less suitable for both conventional chip removal (machining) techniques and electric discharge machining (EDM). The very low material removal rate (MRR) of the Ti alloys during the EDM process causes prohibitively long machining durations. The goal of this study was to improve the EDM performance of the Ti-6Al-4V alloy by the addition of graphite powder into the kerosene dielectric liquid. The EDM performance was quantified by MRR, tool electrode wear rate (EWR), relative wear (RW), surface roughness and texture properties. The experiments conducted have shown that the use of graphite powder mixed with the kerosene dielectric (GPMKD) during machining considerably increases the MRR, improves the R-a and R-z(DIN) surface roughness and decreases the RW. 3D topographic views of the machined workpiece surfaces attained with GPMKD revealed uniformly distributed surface valleys and peaks over the surface and peaks with short arid round tops since the discharge energy of a spark is distributed over a large area at the machining gap. The experimental results strongly indicate the adaptability of the proposed technique to EDM die sinking and EDM drilling applications of the Ti-6Al-4V alloy in the aerospace industry. The ED machining performance of Ti-6Al-4V alloy using GPMKD is also compared to that of AISI 1040 steel, which is commonly used in EDM applications.