Yazar "Oymak, Mehmet Akif" seçeneğine göre listele

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    Bio-Inspired Graded and Uniform Cylindrical Lattices Fabricated by Material Extrusion 3D Printing: An Experimental and Numerical Investigation
    (Wiley, 2025) Oymak, Mehmet Akif; Bahce, Erkan; Singh, Gurminder
    The main requirements of the biomedical and aerospace industries are new and innovative lightweight materials. Bio-inspired structures, which are inspired by various biological designs, have demonstrated notable advancements over traditional lightweight structures. In this study, bioinspired uniform and graded cylindrical triply periodic minimal surface (TPMS) and strut-based lattice structures were studied for their mechanical qualities and energy absorption capacities fabricated by material extrusion 3D printing using PLA material. It was found that the cylindrical TPMS diamond lattice achieved maximum stress of 78.5 MPa and absorbed 19.14 MJ/m3 of energy, outperforming strut-based designs with a 48% higher energy absorption than cylindrical BCC lattice structure. Graded designs further improve energy absorption through a better stress distribution. The findings validated the Gibson-Ashby model, highlighting the enhanced load distribution and stress transfer in the strut-based and TPMS diamond structures. The finite element (FE) model results closely matched the experimental data, confirming its predictive reliability with a maximum error of energy absorption of 7.7%, elastic modulus of 6.9%, and plateau stress of 4.7%. These insights underscore the superior energy absorption and mechanical stability of cylindrical TPMS diamond lattices, indicating their potential for satisfying stringent industrial and technical performance requirements. The novelty of these designs lies in their bioinspired structures and significant enhancements in mechanical performance and energy absorption. Future research should build on these results to design efficient materials tailored to specific needs using FE models to optimize development processes before experimental testing.
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    CASE STUDY OF A DISTAL FEMUR TI6Al4V LOCKED COMPRESSION PLATE FAILURE SURFACE INVESTIGATION AND FINITE ELEMENT ANALYSIS
    (World Scientific Publ Co Pte Ltd, 2024) Can, Murat; Oymak, Mehmet Akif; Koluacik, Serdar; Bahce, Erkan; Uzunyol, Omer Faruk
    In this study, the failure of locking compression plates (LCP) used in the treatment of bone fractures resulting from falls in orthopedic patients at Malatya Training and Research Hospital was investigated. The researchers examined the fracture surface of the failed Ti6Al4V LCP using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) images. The fracture pattern of the plate caused by the fall was replicated in a computer-aided design (CAD) model, obtained through three-dimensional (3D) scanning. Additionally, a CAD model of the femur bone was created using magnetic resonance (MR) images. The assembled images of the replicated fracture and the femur bone were used to simulate the application of locked and unlocked compression screws. Considering the weight-bearing load on a human femur, a linear load of 1200 N and 300 N iliopsoas 300 N abductor 600 N hip contact and 70 N tensor fascia latea walking loads had been applied using finite element analysis (FEA). The researchers analyzed the total deformations, von Mises stress, and principal stresses of the plate. When FEA was conducted with walking and body forces applied, it was observed that the walking forces resulted in a 20% higher von Mises stress and a 22.5% greater total deformation 15% low cycle fatigue compared to the body force. During the analysis with walking forces applied, it was noticed that the maximum von Mises stresses on the LCP and the point where fatigue initiation began coincided with the fracture site of the LCP in the patient's body. However, this observation was in contrast to the analysis with body loads applied.
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    Eklemeli imalat ile üretilen kobalt krom alaşımlarının mikroişlenebilirliğinin araştırılması
    (İnönü Üniversitesi, 2021) Oymak, Mehmet Akif; Gezer, İbrahim
    havacılık, otomotiv ve biyomedikal olmak üzere birçok farklı alanlarda eklemeli imalat kullanımı artmaktadır. Biyomedikal alanda eklemeli imalatı geleneksel imalattan ayıran en önemli özellik hastanın durumuna ve vücudun kompleks anatomik bölgelerine uygun şekilde cihazların üretilmesine olanak sağlamasıdır. Bu nedenle tıbbi cihazların üretimi için eklemeli imalat ile üretim sürecinin incelenmesi bu uygulamalar için optimize edilmiş üretim sisteminin tanımlanması önemli bir araştırma konusudur. Eklemeli imalat, metal tozunun katman katman lazer ile eritilerek istenen parçanın oluşmasını sağlamaktadır. Katmanlı üretimin doğal bir sonucu olarak boyutsal hassasiyet, yüzey kalitesi ve sertliği ile ilgili problemler yaşanmaktadır. Özellikle yüksek hassasiyet gerektiğinde veya parçaların fonksiyonel mikro ölçekli özelliklere ihtiyaç duyduğu durumlarda eklemeli imalatın dezavantajları vardır. Bu nedenle parça eklemeli imalat ile oluşturulsa bile, bu işlem zincirinde özel nitelikler üretmek, pürüzsüzlük veya yüzey mekanik özellikleri gibi son parça karakteristiklerini geliştirmek için mikro işlemden faydalanılabilir. Son parçanın özelliklerindeki iyileşme nedeniyle mikro frezeleme bu işlem zincirinde önemli bir yer tutmaktadır. Mükemmel mekanik özellikleri, yüksek korozyon direnci ve yüksek aşınma direnci nedeniyle CoCr alaşımları, etkili biyo malzemeler olarak kabul edilmiştir. Bu çalışmada mikro işleme yapacağımız CoCr alaşım numuneleri Seçici Lazer Ergitme (SLE) ve döküm yöntemleri kullanılarak üretilmektedir. Eklemeli imalat ile üretilen Co-Cr alaşımlarının mikro kesilmesinde yer alan temel mekanizmalar hakkında sınırlı araştırmalar bildirilmiştir. Bu nedenle Co-Cr alaşımlarının mikro işlenmesinde kesme mekanizmaları hakkında temel bilgiler sunmaya çalışılmaktadır. Ayrıca farklı parametrelerde oluşacak yapısal değişiklikleri sıcaklık, gerilme, yüzey kalitesi, çapak ve talaş oluşumu gibi üretim sürekliliğini etkileyen faktörler karşılaştırılıp yorumlanarak üretim optimizasyonu belirlenmiştir. Mikro frezeleme deneyi sırasında oluşan sıcaklıklar ve Von mises gerilmeleri sonlu elemanlar yöntemi ile analiz edilerek deneysel sonuçlarla karşılaştırılmıştır. Anahtar Kelimeler: Mikro frezeleme, CoCr, Eklemeli İmalat, Seçmeli lazer ergitme, Sonlu elemanlar yöntemi
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    Experimental and numerical study on micro-milling of CoCrW alloy produced by selective laser melting and casting
    (Sage Publications Ltd, 2024) Oymak, Mehmet Akif; Bahce, Erkan; Gezer, Ibrahim
    CoCrW can be produced using Additive Manufacturing (AM), while casting methods are commonly used for applications such as dental prostheses. However, rapid heating and cooling during AM production can lead to internal defects, micro-cracks, and shrinkage. Micro-milling can help enhance the material's structure and impart micro-scale properties. This study aimed to investigate the micro-milling properties of CoCrW products manufactured using AM and compare them with materials produced by casting. Numerical models and experimental studies were conducted to examine the differences. Results showed that CoCr alloys produced with AM exhibited 25%-30% lower burr formations, while CoCrW produced by casting had 2%-5% lower surface roughness. Micro-milling experiments demonstrated that a feed rate of 2.5 mu m/tooth resulted in 35%-40% more burr formation and surface roughness compared to a feed rate of 5 mu m/tooth in both SLM and casting methods, attributed to the cutting edge radius. The cutting temperature and top burr height were analyzed using finite element simulations and experimental methods. It was observed that the maximum temperature in CoCrW produced by casting was 6%-15% higher than that in the SLM method. The finite element analyses and experiments revealed a difference of 4%-7% in maximum temperatures and top burr height.
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    Finite element analysis of lattice designed lumbar interbody cage based on the additive manufacturing
    (Sage Publications Ltd, 2023) Bozyigit, Bulent; Oymak, Mehmet Akif; Bahce, Erkan; Uzunyol, Omer Faruk
    Additive manufacturing (AM) methods, which facilitate the production of complex structures with different geometries, have been used in producing interbody cages in recent years. In this study, the effects of Ti6Al4V alloy interbody lattice designed fusion cages between the third and fourth lumbar vertebrae where degenerative disc diseases occur were investigated using the finite element method. Face centered cubic (FCC), body centered cubic (BCC), and diamond structures were selected as the lattice structure suitable for the interbody cage. A kidney shaped interbody lumbar cage was designed. The designated lattice structures were selected by adjusting the cell sizes suitable for the designed geometry, and the mesh configuration was made by the lumbar lattice structure. 400N Axial force and 7.5 N.m moments were applied to the spine according to lateral bending, flexion, and torsion. 400N axial force and 7.5 N.m flexion moment is shown high strain and total deformation then lateral bending and torsion on BCC FCC and diamond lattice structured interbody cages. In addition, the effects of lattice structures under high compression forces were investigated by applying 1000N force to the lattice structures. When von Mises stresses were examined, lower von Mises stress and strains were observed in the BCC structure. However, a lower total deformation was observed in the FCC. Due to the design of the BCC and the diamond structure, it is assumed that bone implant adhesion will increase. In the finite element analysis (FEA), the best results were shown in BCC structures.
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    Investigation Of Cryogenic Cooling Effect With Finite Element Method In Micro Milling Of Ti6Al4V Material
    (2021) Oymak, Mehmet Akif; Bahçe, Erkan; Gezer, İbrahim
    The objective of this study is to see for micro-milling of Ti6Al4V in the different parameters, how wear occurs on the face of the tool and how to evolve cutting temperature, forces, and chip formations with FEM. The effects of dry, liquid coolant and LN2-based cryogenic cooling applications at 50,100,150 m/s cutting speeds and 1,2,3 ?m/dev feed rate were compared in micro-milling of Ti6Al4V alloy. At different parameters, internal and workpiece-cutting edges cryogenic (wacec) are simulated temperatures were observed. Cryogenic cooling, dry and liquid coolant applications perceived that tool wear, chip formation, strain, stresses, and shear forces interpreted with the FEM. Also, a mesh model based on Arbitrary Lagrangian-Eulerian (ALE) simulations and the Johnson-Cook Plasticity model for material plasticity failure criterion are used in this study. As a result, indicated that at the cutting velocity of 100 m/min, cryogenic cooling on the workpiece and cutting edges has caused into decreasing %57 of cutting temperature also by %54 lower tool wear was observed on the internal tool cryogenic, by %15 the shear stresses decreased on wacec in comparison to dry cutting.
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    Patient-Specific Lattice Cage Design for Cervical Spinal Fusion
    (Turkish Neurosurgical Soc, 2026) Bozyigit, Bulent; Oymak, Mehmet Akif; Bahce, Erkan; Singh, Gurminder
    AIM: To propose a patient-specific interbody cage with graded stiffness distributions analogous to the Young's modulus of the cervical spinal bone interface in order to improve mechanical compatibility, promote physiological load sharing, and enhance osseointegration. MATERIAL and METHODS: A synthetic database of spinal bone Young modulus values was used, incorporating anatomical regions (cervical, thoracic, lumbar) and patient-specific factors (age, bone density, health status). A parametric generative design approach allowed dynamic modification of lattice unit cell geometry to achieve target stiffness values (200-3000 MPa) while preserving structural integrity. RESULTS: Finite element endplate analysis demonstrated a 30%-50% reduction in stress shielding compared with conventional solid or homogeneous mesh lattices. Additively manufactured prototypes showed tunable stiffness-porosity trade-offs, achieving yield strength >= 150 MPa while supporting osseointegration. CONCLUSION: This study demonstrates improved load distribution and reduced risk of cage collapse compared with cadaveric spine data. Integrating computational design, biomechanical compatibility, and additive manufacturing may facilitate the development of patient-specific spinal implants with superior mechanical and biological performance.