Browsing by Author "Duran, Deniz"
Now showing 1 - 4 of 4
- Results Per Page
- Sort Options
Article Citation Count: 7Determination of Coulomb's Friction Coefficient Directly from Cylinder Compression Tests(Assoc Mechanical Engineers Technicians Slovenia, 2016) Karadoğan, Celalettin; Karadogan, Celalettin; Manufacturing EngineeringIn this paper, a new method is proposed for the determination of Coulomb's friction coefficient directly from cylinder compression tests. It is based on measuring the immigrated contact area (ICA), which is defined as the lateral surface that comes into contact with the platens after deformation. Preliminary sensitivity analyses showed that ICA is only a function of friction and the strain-hardening exponent at room temperature when a power law relation between the true stress and the true plastic strain is considered. Through intensive numerical simulations by using a code-driven simulation environment, an inverse calculation is done which makes the determination of the friction coefficient possible by using ICA and the strain-hardening exponent of the investigated material. At the end of compression, ICA is usually clearly visible without any precautions; thus, a simplified script is supplied which calculates ICA through digital image analysis made on the end faces of the compressed specimens. This paper includes the complete procedure to determine Coulomb's friction coefficient and a script in which the proposed method is embedded entirely. In addition, practical case studies demonstrated the ease of applicability of the proposed method by employing different materials.Conference Object Citation Count: 7A flow stress model for steel in cold forging process range and the associated method for parameter identification(Springer London Ltd, 2018) Şimşir, Caner; Duran, Deniz; Manufacturing EngineeringDetailed thermo-mechanical characterization of DIN 16MnCr5 covering the process range of cold forging applications (0.01 s(-1) 40 s(-1), 25 A degrees C Ta 400 A degrees C) by compression tests revealed flow stress instabilities associated with dynamic strain aging (DSA) which cannot be reproduced by conventional flow stress models. As a remedy, a flow stress model capable of capturing sharp changes in flow stress, strain hardening, and strain rate sensitivity is proposed. Then, a method for parameter identification is presented which can deal with inhomogeneous deformation heating of the specimen at relatively high-strain-rate tests. The presented method involves response surface-based numerical optimization of the flawed compression tests coupled with finite element (FE) simulation. The proposed flow stress model and the extracted parameters are validated in a forward rod extrusion process without using any case-specific determined parameters in FE simulation. A natural agreement is obtained between the experimental and the predicted results in terms of both the force-displacement curve and the part geometry. The authors think that the flow stress instabilities encountered in the cold forging process range may have further consequences in other inverse analysis attempts such as friction coefficient or critical damage parameter determination and that the proper treatment of material data as put forth in this study can improve the predictive capability of process modeling.Article Citation Count: 3Predicting and Measuring Surface Enlargement in Forward Rod Extrusion(Asme, 2016) Özdemir, İzzet; Ozdemir, Izzet; Manufacturing EngineeringSurface enlargement during bulk metal forming processes is one of the key parameters controlling the tribology at the tool-workpiece interface. Not only the surface roughness evolution but also the integrity of the lubricant layer critically reposes on surface enlargement. As an attempt to address this issue, in the first part of this work, a general, deformation gradient based surface enlargement description is implemented in a commercial finite element program. In the second part, forward rod extrusion tests with different area reductions are conducted using customized steel workpieces in which cylindrical copper rods are embedded through the depth. By sectioning the extruded parts and by identifying the position of the copper rods on the lateral surface, average surface enlargement values could be measured locally at different positions along the extrudate. Comparison of experiments and numerical predictions reveal that the deformation gradient based description performs reasonably well in capturing surface enlargement profiles both qualitatively and quantitatively.Master Thesis Soğuk ekstrüzyon analizi(2014) Karadoğan, Celalettin; Karadoğan, Celalettin; Özdemir, İzzet; Manufacturing EngineeringSoğuk ekstrüzyon, bir çubuğun sıkıştırılarak bir kalıp açıklığından geçirilmesi ile daha küçük kesitli ürün elde edildiği soğuk dövme yöntemidir. Bu çalışmada, soğuk ekstrüzyon proseslerinin bugüne kadar yapılan çalışmalarda gözden kaçmış çeşitli yönleri, deneysel ve sayısal olarak, belirli bir kapsama kadar incelenmiştir. Soğuk ekstrüzyon proseslerinin analizi için gerekli, uygun malzeme karakterizasyonu ele alınmıştır. İzotermal akma eğrilerinin hatalı test verisine dayanarak yeniden oluşturulması için bir yöntem önerilmiştir. 16MnCr5 çeliğinde, 200-400°C proses aralığında, malzemenin negatif genleme hızı duyarlılığı sergilediği, beklenmedik bir kararsızlık gözlenmiştir. Bu kararsızlık dinamik genleme yaşlanması ile ilişkilendirilmiştir. Önerilen yöntemin önemi, bir ileri çubuk akıtma örneği ile ortaya konmuştur. Yaygın bir sürtünme tanımlama testi olan çift çanak geriye akıtma testi için, tersine analizde yetersiz malzeme verisi kullanıldığında var olan tehlike vurgulanmıştır. Önemli bir tribolojik parametre olan yüzey genişlemesinin, sonlu eleman analizi çerçevesinde, rastgele deformasyonlar altında değerlendirilmesi tartışılmış ve alternatif bir hesaplama düzeni geliştirilmiştir. Sayısal tahminleri doğrulamak amacıyla deneysel bir yüzey genişlemesi ölçüm yöntemi uygulanmıştır. Yakın dönemde önerilen, yüzey değişimi tabanlı sürtünme modeli incelenmiş ve olası iyileştirmeler yapılmıştır. Kavram kanıtlama çalışması olarak, çoklu alan indirgemeli ileri çubuk akıtma prosesi irdelenmiştir. Ardından, bir ileri çubuk akıtma prosesi için hesaplanan yüzey pürüzlülüğü tahminleri ile deneysel yüzey topografisi ölçümleri karşılaştırılmıştır.