Person: GÜLÇİMEN ÇAKAN, BETÜL
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GÜLÇİMEN ÇAKAN
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BETÜL
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Publication Stress relaxation of 3d printed pla of various infill orientations under tensile and bending loadings(Wiley, 2023-07-18) TÜFEKCİ, KENAN; Çakan, Betül Gülçimen; GÜLÇİMEN ÇAKAN, BETÜL; Küçükakarsu, Volkan Mesut; Mühendislik Fakültesi; Makine Mühendisliği Bölümü; 0000-0001-5358-1396; AAG-7076-2021In recent years, the widespread use of 3D printing technology in various industries has highlighted the crucial issue of how 3D printed polymers behave mechanically when subjected to stress relaxation. The time-independent mechanical properties of these polymers, as well as their stress relaxation behavior, are both affected by the 3D printing parameters used. Therefore, this study examines the stress-relaxation behavior of PLA under tensile and bending loading modes, specifically investigating how different raster orientations affect this behavior. The findings indicate that the +/- 45 degrees infill orientation had the least amount of relaxation in both tensile and bending modes compared to the other orientations. Additionally, there was higher stress relaxation in the bending loading mode across all infill orientations. The findings indicate that the experimental duration should exceed 750 s to achieve an accurate model, as both Maxwell-Weichert elements contribute to stress relaxation during this period. On the other hand, extending the test beyond 20,000 s is not necessary since neither of the elements contributes significantly to stress relaxation.Publication Effects of raster angle on tensile and surface roughness properties of various FDM filaments(Korean Soc Mechanical Engineers, 2021-07-22) Çakan, Betül Gülçimen; GÜLÇİMEN ÇAKAN, BETÜL; Mühendislik Fakültesi; Makine Mühendisliği Bölümü; 0000-0003-1739-1143; AFD-6959-2022Parts produced by FDM (fused deposition modelling) technique, where polymer filaments are used, are anisotropic and their properties vary depending on the printing parameters, one of which is raster angle. In this study, the effects of this parameter on the tensile and the surface roughness properties were investigated. It was determined that the ultimate tensile strength (UTS) decreased with increasing raster angle; hence, 0 degrees raster angle where tensile loading direction is parallel to the raster yielded the highest strength. Besides +/- 45 degrees raster angle resulted the most ductile behaviour with the highest fracture strains. Fracture occurred due to raster failure for 0 degrees raster angle but for 90 degrees raster angle, it was due to the failure of the interlayer raster bonds. In the case of +/- 45 degrees, both of the failure mechanisms were effective. Surface roughness values increased up to 7 mu m when measurement was perpendicular to the raster and dropped below 1 mu m when it was parallel to the raster.Publication Experimental and numerical investigation of in-plane and out-of-plane impact behaviour of auxetic honeycomb boxes produced by material extrusion(Gazi Üniversitesi, 2021-02-21) Çakan, Betül Gülçimen; Ensarioğlu, Cihat; Küçükakarsu, Volkan M.; Tekin, İbrahim E.; Çakır, M. Cemal; GÜLÇİMEN ÇAKAN, BETÜL; ENSARİOĞLU, CİHAT; Küçükakarsu, Volkan M.; Tekin, İbrahim E.; ÇAKIR, MUSTAFA CEMAL; Mühendislik Fakültesi; Makine Mühendisliği Bölümü; 0000-0003-4118-8639; 0000-0003-1739-1143; F-9772-2018; AFD-6959-2022; DAO-6186-2022; HQW-4065-2023; JIT-5147-2023Auxetic structures, which have a negative Poisson's ratio, have good mechanical energy/impact absorption properties. These structures have found application in sandwich composites in the aerospace and defence industries, in the production of armour or protective sports equipment. In this study, the mechanical behaviour of the auxetic honeycomb structure in different directions (in-plane and out-of-plane) under impact loading was investigated. For the in-plane (x and y) and out-of-plane (z) directions, boxes with an auxetic honeycomb structure were produced by material extrusion method using Power ABS filament. In the experimental study, dynamic tests were carried out with a drop test machine. Besides, explicit analyses were performed by creating finite element models for these 3 directions. The experimental and numerical results have shown that the energy absorption property of auxetic honeycomb geometry is superior in the case of out-of-plane loading, in agreement with each other. In in-plane loadings, crush force efficiency (CFE) and crush forces were lower.Publication Effects of raster angle on tensile and surface roughness properties of various FDM filaments(Korean Soc Mechanical Engineers, 2021-07-22) Çakan, Betül Gülçimen; GÜLÇİMEN ÇAKAN, BETÜL; Mühendislik Fakültesi; Makine Mühendisliği Bölümü; AFD-6959-2022Parts produced by FDM (fused deposition modelling) technique, where polymer filaments are used, are anisotropic and their properties vary depending on the printing parameters, one of which is raster angle. In this study, the effects of this parameter on the tensile and the surface roughness properties were investigated. It was determined that the ultimate tensile strength (UTS) decreased with increasing raster angle; hence, 0 degrees raster angle where tensile loading direction is parallel to the raster yielded the highest strength. Besides +/- 45 degrees raster angle resulted the most ductile behaviour with the highest fracture strains. Fracture occurred due to raster failure for 0 degrees raster angle but for 90 degrees raster angle, it was due to the failure of the interlayer raster bonds. In the case of +/- 45 degrees, both of the failure mechanisms were effective. Surface roughness values increased up to 7 mu m when measurement was perpendicular to the raster and dropped below 1 mu m when it was parallel to the raster.Publication Computational modeling of stress development in metatarsals-on the importance of plantar aponeurosis(Amer Scientific Publishers, 2017-12-01) Petershagen, C.; Soyarslan, C.; Bargmann, S.; Çakan, B. Gülçimen; GÜLÇİMEN ÇAKAN, BETÜL; Mühendislik Fakültesi; Makina Mühendisliği Bölümü; AFD-6959-2022Since the initial attempts, mathematical models for feet have become increasingly complex with structural and constitutive enrichments. This study investigates the effect of the plantar aponeurosis of the foot model on the predicted stress development on the metatarsals. To this end, a detailed finite element model with a skeleton, cartilages, soft tissue, plantar aponeurosis and ligaments is constructed, where the topologies of the foot and bones are defined by a CT (Computer Tomography) scan. The test scenario is a standing still, quasi-static loading condition. Results are compared to those of models without plantar aponeurosis. It is shown that, if the plantar aponeurosis is neglected in the finite element model, the predicted bending mode of the metatarsals mistakenly reverses: in the presence of plantar aponeurosis and together with the arching effect, tensile principal stresses prevail at the top of the metatarsals by a bowing out mechanism, whereas in the absence of plantar aponeurosis we observe compressive principal stresses and strains over the same region.Publication An enhanced method to evaluate tensile yield stress by small punch tests using deflection curves(Mdpi, 2020-06-01) Hahner, Peter; Soyarslan, Celal; Bargmann, Swantje; Çakan, Betül Gülçimen; GÜLÇİMEN ÇAKAN, BETÜL; Mühendislik Fakültesi; Makine Mühendisliği Bölümü; 0000-0003-1739-1143; AFD-6959-2022While force-displacement curves are often preferred in Small Punch (SP) tests due to the ease of the experimental set-up, they encompass significant uncertainties arising from frame compliance. In this work, a methodology is presented to predict yield stresses from the force vs. deflection curves. The present method relies on determining different force levels from the initial part of the force-deflection curve to reflect both the slope and the curvature instead of using a single force level only. The predicted yield stresses for different types of materials, that is, low- and high-strength alloys, are found to be in good agreement with the actual proof stresses with a maximum error of 16%.