Browsing by Author "Soyarslan, Celal"

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Citation Count: 1
Analysis of damage in metal forming
(Hanrimwon Publishing Co., 2008) Soyarslan,C.; Erman Tekkaya,A.; Department of Mechatronics Engineering
Investigation of central burst formation in direct extrusion is presented with experimental and numerical studies. On the experimental side, selecting certain unfavorable die angles and reduction ratios from the Chrysler processing standard for chevron-free extrusions curve [1], a set of extrusion tests are performed. Accordingly, chevrons are produced in the first and second pass for 100Cr6 and Cf53, respectively. On the numerical side, a multiplicative finite plasticity framework is coupled with a Lemaitre variant Continuum Damage Mechanics (CDM) model giving account for the crack closure effect and implemented as ABAQUS/VUMAT subroutine. Materializing an explicit finite element scheme, the effects of main process parameters, such as friction, semi-cone angle and reduction ratio on damage accumulation zones and intensities are studied. It is shown that, for the identical geometries, with an appropriately selected crack closure parameter and an element deletion procedure, the discrete periodic cracks can be captured, which are in correlation with the conducted experimental outputs.
Citation Count: 38
Application of Continuum Damage Mechanics in discontinuous crack formation: Forward extrusion chevron
(Wiley-v C H verlag Gmbh, 2008) Soyarslan, Celal; Tekkaya, A. Erman; Akyuz, Ugurhan; Department of Mechatronics Engineering; Manufacturing Engineering
Materializing Continuum Damage Mechanics (CDM), numerical modeling of discrete internal cracks, namely central bursts, in direct forward extrusion process is presented. Accordingly, in a thermodynamically consistent setting, a local Lemaitre variant damage model with quasi-unilateral evolution is coupled with hyperelastic-plasticity. The formulations are constructed in the principal axes where simultaneous local integration schemes are efficiently developed. To this end, the framework is implemented as ABAQUS/VUMAT subroutine to be used in an explicit FE solution scheme, and utilized in direct forward extrusion simulations for bearing steel, 100Cr6. Discontinuous cracks are obtained with the element deletion procedure, where the elements reaching the critical damage value are removed from the mesh. The periodicity of the cracks shows well accordance with the experimental facts. The investigations reveal that, application of the quasi-unilateral conditions together with the crack closure parameter has an indispensable effect on the damage accumulation zones by determining their internal or superficial character. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Citation Count: 0
Elastostatics of star-polygon tile-based architectured planar lattices
(Elsevier Sci Ltd, 2023) Soyarslan, Celal; Gleadall, Andrew; Yan, Jiongyi; Argeso, Hakan; Sozumert, Emrah; Manufacturing Engineering; Department of Mechatronics Engineering
A panoptic view of architectured planar lattices based on star-polygon tilings was developed. Four starpolygon-based lattice sub-families, formed of systematically arranged triangles, squares, or hexagons, were investigated numerically and experimentally. Finite-element-based homogenization allowed computation of Poisson's ratio, elastic modulus, shear modulus, and planar bulk modulus. A comprehensive understanding of the range of properties and micromechanical deformation mechanisms was developed. Adjusting the star-polygon angle achieved an over 250-fold range in elastic modulus, over a 10-fold range in density, and a range of -0.919 to +0.988 for Poisson's ratio. Additively manufactured lattices, achieved by novel printing strategies, showed good agreement in properties. Parametric additive manufacturing procedures for all lattices are available on www.fullcontrol.xyz/#/models/1d3528. Three of the four sub-families exhibited in-plane elastic isotropy. One showed high stiffness with auxeticity at low density and a primarily axial deformation mode as opposed to bending deformation for the other three lattices. The range of achievable properties, demonstrated with property maps, proves the extension of the conventional material-property space. Lattice metamaterials with Triangle-Triangle, Kagome, Hexagonal, Square, Truncated Archimedean, Triangular, and Truncated Hexagonal topologies have been studied in the literature individually. Here, it is shown that these structures belong to the presented overarching lattice family. (c) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Citation Count: 14
Finite deformation plasticity coupled with isotropic damage: Formulation in principal axes and applications
(Elsevier Science Bv, 2010) Soyarslan, C.; Tekkaya, A. E.; Manufacturing Engineering; Department of Mechatronics Engineering
A local, isotropic damage coupled hyperelastic-plastic framework is formulated in principal axes. It is shown that, in a functional setting, treatment of many damage growth models, including those originated from phenomenological models (with formal thermodynamical derivations), micromechanics or fracture criteria, proposed in the literature, is possible. As a model problem, a Lemaitre-variant damage model with quasi-unilateral damage evolutionary forms is given with special emphasis on the feasibility of formulations in principal axes. To this end, closed form expression for the inelastic tangent moduli, consistent with the linearization of the closest point projection algorithm, is derived. It is shown that, generally, even in the absence of quasi-unilateral damage evolutionary conditions, the consistent tangent moduli are unsymmetric. The model is implemented as a user defined material subroutine (UMAT) for ABAQUS/Standard. The predictive capability of the selected model problem is studied through axi-symmetric application problems involving forward extrusion of a cylindrical billet, upsetting of a tapered specimen and tension of a notched specimen, in which characteristic failure mechanisms are observed. (C) 2010 Elsevier B.V. All rights reserved.
Citation Count: 1
Finite element analysis of stress distribution on modified retentive tips of bar clasp
(Taylor & Francis Ltd, 2012) Oyar, P.; Soyarslan, C.; Can, G.; Demirci, E.; Department of Mechatronics Engineering
This study used finite element analysis to evaluate the retentive tips of bar clasps made from different alloys and using different designs in order to determine whether or not different materials and tip forms are suitable for bar clasp applications. Co-Cr, Ti and Type IV Au alloys were selected based on their physical and mechanical properties. The 3D finite element models of three different bar clasp retentive tip geometries prepared from Co-Cr, Ti and Type IV Au alloys were constructed using the finite element software package MSC. Marc. Analysis of a concentrated load of 5N applied to the removable partial denture approach arms in an occlusal direction was performed. Although stress distribution and localisation within bar clasps with different retentive tips were observed to be similar and were concentrated in the approach arm, stress intensities differed in all models.
Citation Count: 15
Prevention of Internal Cracks in Forward Extrusion by Means of Counter Pressure: A Numerical Treatise
(verlag Stahleisen Mbh, 2009) Soyarslan, C.; Tekkaya, A. E.; Manufacturing Engineering; Department of Mechatronics Engineering
In the context of forward bulk extrusion, where product defects are frequently observed, the effect of counter pressure on damage accumulation materializing a Continuum Damage Mechanics (CDM) approach is presented. A Lemaitre variant damage model accounting for unilateral damage evolution coupled with a multiplicative finite plasticity is utilized for this purpose. After a presentation of the crack governing mechanism, it is demonstrated that application of counter pressure introduces a marked decrease in the central damage accumulation, which in turn increases the formability of the material through keeping the tensile triaxiality in tolerable limits. It is also shown that, for a crack involving process, through systematic increase of the counter pressure, the crack sizes diminish; and at a certain level of counter pressure chevron cracks can be completely avoided.
Citation Count: 13
Skeletonization-based beam finite element models for stochastic bicontinuous materials: Application to simulations of nanoporous gold
(Cambridge Univ Press, 2018) Soyarslan, Celal; Argeso, Hakan; Borgmann, Swantje; Manufacturing Engineering; Department of Mechatronics Engineering
An efficient representative volume element generation strategy is developed in modeling nanoporous materials. It uses periodic 3D beam finite element (FE) models derived from skeletonization of spinodal-like stochastic microstructures produced by a leveled random field. To mimic stiffening with agglomeration of the mass at junctions, an increased Young's modulus is assigned to the elements within the junction zone. The effective Young's modulus, Poisson's ratio, and universal anisotropy index are computed. A good agreement of the Young's modulus predictions with those obtained from experimental results for phase volume fractions 0.20 < phi(B) < 0.50 is observed. Moreover, the elastic anisotropy index of the generated beam networks shows sufficient proximity to isotropy. Finally, it is demonstrated that, as compared to the simulation statistics of voxel-FE models, for the beam-FE models over 500-fold computational acceleration with 250-fold less memory requirement is provided.
Citation Count: 0
Soğuk dövmede sürekli ortamlar hasar mekaniği (SOHM) uygulamaları: Bölüm I-ekstrüzyonda v-şeklindeki merkezi kırık oluşumunun modellenmesi
(2008) Soyarslan, C.; Tekkaya, A.e.; Akyüz, U.; Department of Mechatronics Engineering
Bu çalışmada, soğuk ileriye çubuk akıtma işleminde görülen iç çatlakların SOHM vasıtası ile incelenmesi amaçlanmıştır. Bu amacı gerçekleştirmek adına hemen hemen-tek yönlü hasar evrimine izin veren Lemaitre tipi bir matematiksel hasar modeli, deformasyon gradyanının çarpmalı faktorizasyonuna dayanan sonlu hiperelastik plastisite ile eşleştirilmiş ve geliştirilen yapı, bir ticari sonlu elemanlar programı olan ABAQUS/Explicit için VUMAT kullanıcı tanımlı malzeme alt-programı olarak uygulanmıştır. Bu alt-program vasıtası ile gerçekleştirilen benzetimlerde 100Cr6 çeliği için tek aşamalı ileriye çubuk akıtma işlemi için merkezi hasar birikimi ve kırık oluşumu incelenmiştir. Gösterilmiştir ki, uygun sürtünme değerleri için deneysel verilerle de uyum gösteren gözlemlere göre, ileriye çubuk akıtma işlemi sırasında, plastik şekillenme bölgesinde meydana gelen pozitif asal gerilmeler malzeme şekillenebilirliğini kayda değer bir şekilde azaltmakta ve nihayetinde v-şeklinde iç kırıklara neden olmaktadır. Ayrıca oluşan kırıkların kuvvet-yer değiştirme eğrileri üzerindeki etkisi incelenmiştir.
Citation Count: 0
Soğuk dövmede sürekli ortamlar hasar mekaniği (SOHM) uygulamaları: Bölüm II-Ekstrüzyonda v-şeklindeki merkezi kırık oluşumunun önlenmesi
(2008) Soyarslan, C.; Tekkaya, A.e.; Akyüz, U.; Department of Mechatronics Engineering
Çalışmanın bu kısmında, soğuk ileriye çubuk akıtma işleminde görülen merkezi kırıkların, uygun işlem parametrelerinin belirlenmesi ile önlenmesine yönelik, SOHM'ne dayanan sayısal çalışmalara yer verilmiştir. Kırık kapanma katsayısı, pekleşme üstel fonksiyon katsayısı, sürtünme, kalıp açısı ve alan indirim oranı, uygulanan ters basınç değeri gibi parametrelerin merkezi hasar birikimine tesiri, kapsamlı \"bir biçimde incelenmiştir. Gösterilmiştir ki, kalıp açısı-alan indirim oranı uzayını tarayan bir grup sayısal analizle, işlemin hatasız gerçekleşeceği sınır geometri değerlerinin ekonomik olarak temini mümkündür. Önerilen sayısal yöntemin çekici yönlerinden biri de, farklı işlem koşullarını aynı sistematik içerisinde kapsayabilecek genellikte olmasıdır. Buna örnek olarak işlem tasarımına eklenen ters basınç uygulamalarının hasar birikimine etkisi sayısal olarak modellenmiş, uygun karşı basınç değerlerinde iç kırıkların engellenebileceği gösterilmiştir.
Yumuşamalı plastisite için viskoz ve yerel olmayan entegral tip regülarizasyon yöntemleri: (Infinitesimal genlemeli çatı)
(2009) Kayhan, Erdem; Soyarslan, Celal; Airframe and Powerplant Maintenance; Department of Mechatronics Engineering
Genlemeli yumuşama davranışını gösteren malzemeler için, klasik yerel süreklilik modellemesinin kullanıldığı sonlu elemanlar metodu, örgüye bağlı sonuçlar vermeye yatkındır. Malzeme temel modelinin kurulumu, termodinamik yaklaşımla iç değişkenlere bağlı olarak gerçekleştirilmiştir, bu çalışma, lokalizasyonu sınırlandıran, uygun örgü boyutunun kullanılmasına ve bir tek sonucun elde edileceği çözüme odaklıdır.Bu çerçevede, yerel olmayan entegral tip ortalama ve viskoz regülarizasyon yöntemleri geliştirilmiştir. Yumuşamalı malzeme davranışı, infinitesimal genlemeli çatı için plastisite teorisinin uyarlanması ile açıklanmıştır. Yerel entegrasyonun sayısal hesaplamasında, kapalı Euler geri yerine koyma tekniği temel alınmıştır. Bu yöntemde en yakın noktaya yansıtma esas alınır. Buraya kadar geliştirilmiş olan çözüm yöntemleri, ABAQUS için kullanıcı tanımlı malzeme arayüz yazılımına dönüştürülmüştür. Yazılımın doğrulanmasından sonra, iki boyutlu bir örnek kullanılarak, yerel olmayan ortalama yönteminin başarısı, yerel yaklaşımlardan elde edilen sonuçlar ile karşılaştırılarak gösterilmiştir. Her iki yöntemden elde edilen sonuçlar karşılaştırılarak, detaylı olarak değerlendirilmiştir..