Profile URL: https://hdl.handle.net/20.500.12573/2807
Job Title:Dr. Öğr. Üyesi
Email Address:yilmaz.cagatay@agu.edu.tr
Main Affiliation:02.06. Makine Mühendisliği
Status: Current Staff
ORCID:
0000-0002-8063-151X
0000-0002-8063-151XScopus ID:
57206138403
57206138403YÖK Akademik: E574795FFEBFBD1C
Google Scholar:
q00FutwAAAAJ
q00FutwAAAAJWeb of Science ID:
ABI-5043-2020
ABI-5043-2020Name Variants:
Yilmaz, Cagatay Çağatay Yılmaz
15 results
Scholarly Output Search Results
Now showing 1 - 10 of 15
Article Performance Evaluation of Energy Companies With a Novel Integrated Multi- Criteria Decision Making Method(Kafkas University Iibf, 2022) Madenoglu, Fatma Selen; Unlusoy, Omer Faruk; Yilmaz, CagatayFinancial statements are an important tool for assessing and analyzing an organization's financial performance. Financial performance analysis allows for an accurate and appropriate appraisal of an organization's performance. The evaluation procedure must be thoroughly stated because financial performance indicators represent a company's competitiveness. This study provides a novel integrated multi-criteria decision-making method for analyzing an organization's financial performance. The applicability of the proposed method is assessed employing financial ratios that are integrated to generate a financial performance score for eight well-known Turkish energy companies. The criteria are weighted using the entropy method in the proposed method. The multi- attributive border approximation area comparison (MABAC) method is used to rank the companies. As the weights of the criteria have an impact on the ranking outcomes, a sensitivity analysis of the weights is performed. We also exhibit a comparison analysis of energy company rankings to validate the proposed approach's results using four MCDM methods: ELECTRE, MAUT, TOPSIS, and WASPAS. In addition, an alternative weighting method is also used to evaluate the results. The results show that the proposed method is an effective MCDM for coping with evaluation problems.Article Citation - WoS: 11Citation - Scopus: 11Monitoring and Verification of Micro-Strain Generated Inside the Laminate Subjected to Thermal Loading Through Fiber Bragg Grating Sensors and Classical Laminate Theory(Wiley, 2023-03-23) Yilmaz, Cagatay; Ali, Hafiz Qasim; Yildiz, MehmetFiber Bragg Grating (FBG) sensors possess enormous potential for the cure monitoring and integrity assessment of Carbon Fiber Reinforced Polymer (CFRP) composites. These sensors can be embedded inside the structure to monitor the strain in the desired region of interest. The strain on an FBG sensor can be calculated by measuring the change in the center wavelength of the sensor. This change in center wavelength is a function of temperature and mechanical strain. Therefore, temperature compensation is necessary for a precise mechanical strain measurement with an FBG sensor. In this study, FBG sensors are embedded in different layers of the CFRP laminate to record the mechanical strain caused by the thermal expansion, which happens under the influence of temperature. Classical laminate theory (CLT) is implemented to assess the accuracy of FBG sensor measurements and the strain data acquired from both FBG sensor and CLT correlates. Furthermore, a resistive strain gauge is deployed to measure the strain under the influence of temperature. It is depicted that strain values recorded by the strain gauge under the influence of the temperature do not agree with the strain measured by CLT, and an error of 150% occurs among their values.Article ASTM-D638 Numune Tipinin Erimiş Biriktirme Modelleme 3D Baskılı PLA Numunelerinin Çekme Özelliklerine Etkisi(2025) Yilmaz, Cagatay; Eltahir, Sara Saeed Abdulrahman; Gomaa, RoaaBu araştırma, farklı ASTM-D638 numune türlerinin 3D baskılı PLA malzemelerinin mekanik özelliklerini nasıl etkilediğini incelemektedir. Numune türleri, ASTM-D638 standartlarında tanımlandığı gibi, beş farklı türü içeren, mekanik testlerde kullanılan test numunelerinin belirli konfigürasyonlarını ifade eder: Tip I – Tip V. Bu standart, tutarlı ve karşılaştırılabilir test prosedürlerini sağlamak için çeşitli numune geometrilerini ve boyutlarını özetlemektedir. Polilaktik asit (PLA) ile ilgili çalışmalar. Bilgisayar destekli tasarım (CAD) modelleri oluşturulur ve PLA numuneleri üretmek için Erimiş Biriktirme Modelleme (FDM) 3D baskı kullanılır. Numunelerin mukavemetini ve gerinimini ölçmek için sırasıyla çekme testi ve Dijital Görüntü Korelasyonu (DIC) analizi yapılır. Çalışma, numune türünün parça özellikleri üzerindeki etkisine ilişkin kapsamlı veriler sağlamayı ve DIC ve akıllı telefon kullanılarak uygun maliyetli bir gerinim ölçüm yöntemi göstermeyi amaçlıyor. Metodoloji, CAD modellemeyi, 3D yazdırmayı, yüzey hazırlığını, çekme testini, Ncorr kullanılarak DIC analizini ve MATLAB veri işlemeyi içerir. Sonuçlar, Tip I ve Tip II'nin sırasıyla 43,179 MPa ve 43,164 MPa ile en yüksek nihai gerilme mukavemetini (UTS) sergilediği gerilim-gerinim eğrilerini ve ortalama gerinim değerlerini gösterir. Ancak Tip V, kısa baskı süresi ve Tip I'e göre 5 kat daha az olan düşük filament kullanımı ve 42.640 MPa'lık makul UTS'si nedeniyle en optimum seçenektir. Bu araştırma, numune tasarımının 3D baskılı parça özellikleri üzerindeki etkisine ilişkin bilgi boşluğunu doldurarak gelecekteki araştırmalar için değerli bilgiler sağlıyor.Article Citation - WoS: 12Citation - Scopus: 14The Effect of Different Tabbing Methods on the Damage Progression and Failure of Carbon Fiber Reinforced Composite Material Under Tensile Loading(Elsevier Sci Ltd, 2022-07) Ali, Hafiz Qasim; Yilmaz, Cagatay; Yildiz, MehmetComposites are well-known and widely used materials due to their anisotropic nature and high strength-to-weight ratio; therefore, the mechanical performance of these materials is crucial. Precise tensile testing is essential to obtain material properties that are crucial for the design stage of composite structures. This study is an effort to investigate the effect of adhesive materials used for tabbing process, which is necessary for the tensile testing procedure. Araldite and AF 163-2k film are used as the adhesive film, whereas in the case of AF 163-2k, tabbing is done through two different procedures (Jig and corner holes method). Apart from the tensile per-formance, strain distribution and damage progression are monitored simultaneously using digital image corre-lation (DIC) and acoustic emission (AE) analysis. It is observed that there is no significant difference in the ultimate tensile strength of these composites tabbed with different adhesives and procedures. Nevertheless, the first major failure strength is much higher in Araldite tabbed specimens compared to AF 163-2k film (the first major failure activity is defined as a point at which material loses its integrity, especially when considering structural or aerospace applications). Also, strain distribution throughout the gauge length recorded via DIC is appreciably different, which is attributed to damage accumulation and progression monitored by AE analysis. The frequency-based analysis of AE data is performed to classify the damage, and cumulative energy is correlated with the DIC to navigate the failure activity at different times and stress levels.Article A Parametric Study for Drilling High Quality Holes on Glass Fiber Composites(2022) Yilmaz, Cagatay; Kesriklioglu, SinanThe objective of this study is to investigate the effect of cutting parameters on the qual- ity of holes drilled in a glass fiber reinforced thermoset polymer with the delamination factor defined as the ratio of intended hole diameter to the diameter of the maximum area which contains both hole and delaminated area. For this purpose, Taguchi's L9 or- thogonal array was used to design the experiments and optimize the drilling parameters. 5 mm twist drill bits were used to drill the holes at various feeds and spindle speeds. The maximum diameters on the inlet and outlet sides of the holes drilled into the composite plates were then measured with an optical microscope to analyze the influence of the drilling parameters on the machining damage. The smallest delaminated area on the front and back sides of the composite plate was achieved with the lowest feed (0.05 mm/rev) for the drilling parameters used in this study. Even though the spindle speed was increased from 318 rpm to 2930 rpm at a constant feed of 0.05 mm/rev, it reduces the maximum diameter on the front and back sides by 9 μm and 266 μm, respectively. The obtained results showed that the material removal rates in the drilling of the glass fiber reinforced thermoset polymers can be increased significantly by setting the optimized process pa- rameters without adversely affecting the hole quality.Article Experimental Comparative Analysis of Hole-Making Strategies and Cutting Parameters on Flexural Properties and Induced Delamination in S2 Glass and Basalt Fiber-Reinforced Polymers(John Wiley and Sons Inc, 2026) Eltahir, Sara Saeed Abdulrahman; Yilmaz, Cagatay; Kesriklioglu, SinanOpen holes are often required in the applications of fiber-reinforced polymers (FRP). However, machining them leads to fiber and matrix damage, reducing the overall quality of composites. The novelty of this study lies in investigating the influence of multiple hole machining strategies under varying feed rates and cutting speeds on the flexural strength, chord modulus and hole quality for S2-Glass (S2-GFRP) and basalt fiber-reinforced polymers (BFRP), followed by three-point bending tests and statistical analysis to determine the optimum machining parameters in terms of flexural properties, delamination, and time efficiency. Findings indicate that conventional milling yields an increase in the flexural strength and chord modulus by 22.2 MPa and 1.9 GPa, respectively, for S2 GFRP. While climb milling performs best for BFRP, enhancing flexural performance by 7.6 MPa and 0.4 GPa. Direct drilling at high feed rate and cutting speed shows the poorest performance. Hole machining at low feed rate using climb milling minimizes delamination at the entrance by 14.8% for S2 GFRP and by 2.7% for BFRP using conventional milling. At the exit, helical milling at a low feed rate suppresses delamination damage by 58.5% and 10.7% for S2 GFRP and BFRP. The most time-efficient method is direct drilling at a feed rate of 0.075 mm/rev and cutting speed of 75 m/min or climb milling with same feed rate, but 25 m/min cutting speed. Within the tested ranges, the optimized drilling setup significantly improved structural performance of S2-GFRP and GFRP, confirming the effectiveness of the proposed experimental-statistical framework.Article Citation - Scopus: 1Failure Analysis of Fused Deposition Modeling 3D Printed Poly Lactic Acid Polymer(Sage Publications Ltd, 2025) Yilmaz, Cagatay; Eltahir, Sara Saeed AbdulrahmanAdditive manufacturing, commonly known as 3D printing (AM), has emerged as one of the most transformative technological advances in the last few decades in global manufacturing, as it allows for the production of intricate components without the use of costly molds. Fused Deposition Modeling (FDM) is widely adopted among various AM techniques due to its accessibility and effectiveness. FDM 3D-printed PLA (Poly Lactic Acid) shows a transversely isotopic symmetry similar to laminated composite structures. Therefore, classical lamination theory can be applied to FDM 3D-printed PLA. This study attempts to expand the knowledge by relying on classical lamination theory and several imposed failure theories like maximum stress, Tsai-Hill, Tsai-Wu, and Hashin to determine how FDM 3D printing of PLA fails. We investigate eight different raster orientations (0 degrees, 10 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees) and compare the theoretical prediction of strength with experimental findings. With this comprehensive analysis, we are seeking to better understand the failure analysis of FDM 3D printed PLA. The maximum stress, Tsai-Wu, Tsai-Hill, and Hashin failure theories show good agreement with experimental findings for 0 degrees and 90 degrees raster orientations. As the raster orientation shifts from 0 degrees, the discrepancy between experimental results and theoretical predictions increases, peaks at mid-angles, and then decreases, becoming negligible at 90 degrees.Article Surface Integrity and Tool Wear in S2-GFRP Milling: Experimental and Statistical Evaluation of Cutting Parameters and DLC and TiAlN Tool Coatings(Springer London Ltd, 2026) Danisman, Sengul; Yilmaz, Cagatay; Ersoy, Emin; Kesriklioglu, SinanIn this study, the surface integrity of S2-glass fiber-reinforced polymer (S2-GFRP) composites during milling with carbide cutters was investigated using a two-phase experimental design, focusing on surface roughness (Ra), burr area, and tool wear (VB). In the first phase, using a Taguchi L9 design, the effects of coating type (uncoated, TiAlN, DLC), spindle speed (2000-6000 rpm), and feed rate (0,15-0,25 mm/rev) on Ra and burr area were evaluated. In this short machining range where tool wear was negligible, the optimal combination yielding the lowest Ra (approximate to 0.97 mu m) and the minimum burr area (approximate to 231 mm & sup2;) was determined to be 4000 rpm, 0,15 mm/rev, and the DLC-coated tool. Regarding the effect of tool material on Ra, the DLC-coated tool provided approximately 4 and 2 times better results than the uncoated and TiAlN-coated tools, respectively. In the second phase, experiments extended up to 130 passes with this optimal parameter set showed that Ra increased significantly with increasing VB, and the burr area exhibited threshold-like behavior. In particular, a sudden increase in Ra and the burr area was observed when the VB approximate to threshold of approximately 100 mu m was exceeded; partial regression analyses confirmed different burr-formation tendencies in the low- and high-wear regimes. The results reveal that DLC coating initially provides superior performance in S2-GFRP milling, but surface degradation accelerates after the critical VB threshold.Article Effect of Strain Rate on the Tensile Properties of 3D – Printed PLA Specimens with Fused Deposition Modelling(2024) Yilmaz, Cagatay; Eltahir, Sara Saeed Abdulrahman; Gomaa, RoaaMany engineering applications and industries require components to be lightweight while still maintaining strong mechanical properties. Polylactic acid (PLA) is widely used in additive man- ufacturing due to its biodegradability, ease of printing, and favourable mechanical characteris- tics, making it an in-demand material for various applications. Understanding the influence of strain rate on the tensile properties of PLA is crucial, as it directly affects the material's perfor- mance under different loading conditions. This research investigates the influence of strain rate on the tensile properties of PLA material fabricated through fused deposition modeling (FDM) using Type V ASTM D638 – 14 specimens. Three distinct strain rates (0.8 mm/min, 2 mm/ min, and 20 mm/min) are considered, and Digital Image Correlation (DIC) is employed for ultimate tensile strain analysis. The methodology involves CAD modeling, 3D printing, surface preparation, and tensile testing, with DIC analysis performed using the Ncorr application. Re- sults indicate a linear increase in tensile strength with higher strain rates as the tensile strength increased by 30% from 40.41 MPa at 0.8 mm/min to 52.62 MPa at 20 mm/min. Additionally, Elastic modulus increases with increasing strain rate, rising by approximately 43.5%, from 1.54 GPa at 0.8 mm/min to 2.21 GPa at 20 mm/min. This research contributes valuable insights into the dynamic behavior of FDM-printed PLA under different strain rates, offering implications for material performance in applications requiring diverse loading conditions.Article Application of Hooke’s Law to Angle Ply Lamina(2022) Yilmaz, Cagatay; Ali, Hafiz Qasim; Yildiz, MehmetAerospace-grade carbon fiber reinforced polymer composite plates with four different fiber orientations 0º, 30º, 45ºand 60º is produced with the autoclave curing method and subjected to tensile testing. The stress-strain curves of the composite specimens are compared with Hooke’s law. It is observed that Hooke’s law coincides precisely with the experimental results for samples containing fibers parallel to the loading direction. However, it does not coincide with samples where the fibers make a certain angle with the applied load direction.. Moreover, it is reported that Hooke’s law converges the experimental results for small strain values but diverges significantly from the experimental results at higher strain values.