İlgi alanları

Sürdürülebilir Kalkınma Amaçları

• 1

• MakaleAçık Erişim2026Scopus SJRQ1/r/bayburt/11213
  Effect of fiber architecture and CNT reinforcement on the mechanical behavior and formability of thermoplastic PE composites

  Gavgali, Esma; Dilmec, Murat

  Lightweight thermoplastics with improved mechanical performance and formability are critical for aerospace, defense, and automotive applications. Despite this, the coupled effects of nanoscale carbon nanotube (CNT) reinforcement and fiber architecture on formability-dominated deformation remain insufficiently explored. This study investigates polyethylene (PE) matrix fiber-reinforced composites manufactured with and without CNT modification to clarify these effects. Mechanical behavior was evaluated through tensile, flexural, hardness tests, while biaxial formability was assessed using the Erichsen test. Fracture mechanisms were analyzed by scanning electron microscopy (SEM). The results indicate that CNT addition significantly improved glass fiber laminates, with peak forming loads increasing by up to 152% for plain weaves and 211% for twill weaves. In contrast, carbon fiber laminates showed only marginal improvements (≤5%), attributed to their inherently high interfacial efficiency. The CNT-reinforced twill carbon fiber composite achieved the highest tensile strength (240.32 MPa) and hardness (66.8 Shore D), while the CNT-reinforced plain glass composite exhibited the highest flexural strength (43.19 MPa). SEM observations revealed composites predominantly failed through fiber–matrix debonding, matrix plastic deformation, and fiber pull-out. Overall, the results show that optimizing fiber type, textile architecture, and CNT reinforcement enables PE-based composites with balanced strength, stiffness, and formability for multiaxial loading applications.

  • 
  İncele
• MakaleAçık Erişim2026Scopus SJRQ4/r/bayburt/11052
  Comparative analysis of stress distributions and safety factor in tensile test specimens with different notch and hole geometries by finite element method

  Korkmaz, Sümeyye Erdem; Gavgali, Esma

  This study analyzes the effects of different notch and hole geometries (V-Notched, U-Notched, circular hole) on stress concentration in Ti-6Al-4V (Grade 5) Titanium alloy tensile specimens to provide optimized design recommendations for aerospace and biomedical applications. Finite element method (ANSYS Workbench) was employed to analyze three geometries under 15000 N static tensile loading. Von Mises stress distributions and stress concentration factors (Kt) were calculated and validated against Peterson and Neuber theoretical formulas with average error ±1.5%. Results revealed that V-Notched exhibited highest stress concentration (Kt = 5.78, σmax = 1156 MPa), while circular hole showed lowest (Kt = 2.25, σmax = 454.12 MPa). U-Notched demonstrated intermediate performance (Kt = 2.84, σmax = 995.45 MPa). Increasing notch root radius from 0.5 mm to 2.0 mm achieved 51% reduction in stress concentration factor. Maximum shear stress values were 232.74 MPa, 506.38 MPa, and 640 MPa for circular, U-Notched, and V-Notched respectively, while maximum normal stress values reached 467.06 MPa, 1015.1 MPa, and 1809 MPa. Safety factor analysis showed that circular hole configuration meets aerospace standards (FS = 2.05 > 1.5), while U-Notched (FS = 0.93) and V-Notched (FS = 0.80) fall below minimum safety criteria. U-Notched exhibited highest total displacement (1.210 mm), indicating compliance effects. For aerospace and biomedical applications, circular holes should be preferred over sharp notches (154% stress reduction), and minimum corner radius ≥2.0 mm is recommended. The critical finding that geometric optimization provides 2.6× safety improvement without material changes demonstrates the powerful role of design in structural reliability for weight-critical applications.

  İncele
• MakaleYalnız künye2022Scopus SJRQ2/r/bayburt/11980
  A study on the effects of nanostructure reinforcement on the failure load in adhesively bonded joints after the subjected to fully reversed fatigue load

  Akpinar, Salih; Demir, Kübra; Gavgali, Esma; Yetim, Ali Fatih

  Today, adhesively bonded joints are frequently used in the space and aviation industries. Joints used in these sectors are generally subject to dynamic loads due to environmental factors. This study experimentally and numerically investigated the static tensile loads of adhesively bonded joints after fully reversed (combination of tensile and compressive) fatigue loading where nanoadhesives–obtained by adding carbon nanostructures into aerospace grade structural adhesive–were used to bond the joints. Single lap joint specimens were produced using a nanocomposite adhesive obtained by adding 1 wt. % graphene, 1 wt. % carbon nanotubes-COOH and 1 wt. % fullerene C60 nanostructures to a DP460 structural adhesive. AA2024-T3 aluminum alloy and carbon fiber-reinforced composites (CFRCs) with a plain weave fabric (0/90°) were used as adherend materials. First, static tensile tests were applied to these joints to obtain their failure loads and then fully reversed sinusoidal fatigue tests were applied under a constant load amplitude, a frequency of 20 Hz and a load ratio of R = −1. Considering the failure loads obtained from the static tensile tests, 106 fully reversed fatigue loading cycles were applied–which was accepted as an infinite life–at 400 N, 800 N and 1200 N load levels. The static tensile failure loads and energy values absorbed of these joints were obtained and the change in the failure loads and energy values absorbed of the joints subjected to fatigue was investigated. The static failure loads of aluminum joints bonded with nanoadhesive and subjected to fully reversed fatigue loading increased by approximately 5% to 17%, depending on the nanostructure type added to the adhesive. Moreover, it was observed that there was an increase in loading of approximately 3% to 20% for the nanostructure reinforced joints obtained by using CFRCs with [0/90]6 stacking sequence.

  AtıfScopus24·WoS26·OpenAlex28

  İncele
• MakaleYalnız künye2021Scopus SJRQ1/r/bayburt/13496
  An investigation of the fatigue performance of adhesively bonded step-lap joints: An experimental and numerical analysis

  Gavgali, Esma; Sahin, Resul; Akpinar, Salih

  Adhesively bonded joints are used in many engineering applications and are manufactured by joining various materials together. Static and dynamic analysis of adhesively bonded joints is very important in both scientific and sector studies on these joints. In this study, the static and fatigue strengths of single-lap joints (SLJs) and three-step-lap joints (TSLJs) that were subjected to tensile and four-point bending tests were examined experimentally and numerically. Adhesively bonded joints were produced using DP460 toughened type adhesive and AA2024-T3 aluminum alloy was used as the adherent. Fatigue tests were performed at a loading ratio (R) of 0.1 and a frequency of 10 Hz. As a result, applying a step-lap to the overlap area of adhesively bonded joints considerably increased the tensile static and fatigue strength of the joint. For the single-lap joint, both the static tensile and the tensile fatigue lifetime limit value of the three-step-lap joint increased approximately 100%. One of the reasons for that increase was that the moment effect formed in single lap joints due to the eccentric loading is minimized and the other is that a step-lap applied to the overlap area retards the formation of damage. However, static bending and fatigue strength values of TSLJs significantly decreased compared to those of SLJs. In addition, the results of the experimental and numerical analyses were found to be highly compatible with each other.

  AtıfScopus29·WoS28·OpenAlex35

  İncele
• MakaleYalnız künye2021Scopus SJRQ1/r/bayburt/13416
  The effects of nanostructure additive on fracture strength in adhesively bonded joints subjected to fully reversed four-point bending fatigue load

  Demir, Kübra; Gavgali, Esma; Yetim, Ali Fatih; Akpinar, Salih

  Structural adhesive joints used in aerospace are usually subjected to fatigue loading rather than static loading. This study experimentally and numerically investigated the static four-point bending loads of adhesively bonded joints after fully reversed four-point bend fatigue loading where nanoadhesives – obtained by adding carbon nanostructures into aerospace grade structural adhesive – were used to bond the joints. Single lap joint specimens were produced using a nanocomposite adhesive obtained by adding 1 wt % graphene, 1 wt % carbon nanotubes-COOH and 1 wt % fullerene C60 nanostructures to a DP460 structural adhesive. AA2024-T3 aluminum alloy and carbon fiber-reinforced composites (CFRCs) with a plain weave fabric (0/90°) were used as adherend materials. First, static four-point bending tests were applied to these joints to obtain their strengths and then fully reversed sinusoidal fatigue tests were applied under a constant load amplitude, a frequency of 20 Hz and a load ratio of R = −1. Fatigue tests were performed over 1,000,000 cycles – accepted as an infinite life – at four different load levels by considering the strengths obtained from the static tensile tests. After obtaining the static four-point bending strengths of the joints to which fatigue loading was applied, the changes in the strengths of joints with and without fatigue testing were examined. The static strengths of aluminum joints bonded with nanoadhesive and subjected to fully reversed fatigue loading significant increased, depending on the nanostructure type added to the adhesive. Moreover, such increases in the strengths of joints are highly dependent on the adherend type (composite with [0/90]6 stacking sequence or AA2024-T3 aluminum).

  AtıfScopus34·WoS34·OpenAlex34

  İncele
• MakaleAçık Erişim2019/r/bayburt/15027
  Kum Kalıba Dökülen Farklı Alüminyum Alaşımlarının Dökümünde AL5TI1B ve AL10SR İlavesinin Mikroyapı Özelliklere Etkisinin İncelenmesi

  Colak, Murat; Arslan, Ibrahim; Gavgali, Esma

  Alüminyum alaşımları ağırlıkça hafif olması, yüksek korozyon dayanımı ve alaşımlandırılarak yapı çeliklerinden bile daha fazla mukavemet değerleri kazandırılabilmesi gibi özelliklerinden dolayı birçok sektörde kullanım alanı bulmaktadır. Gelişen teknoloji ile birlikte artan ihtiyaç ve kalite beklentileri doğrultusunda çalışmalar yapılması gerekmektedir. Alüminyum dökümlerinde nihai ürün kalitesini artırmaya yönelik Ti-B ile tane inceltme, modifikasyon çalışmaları dökümhaneler arasında oldukça yaygın uygulamalardır. Ancak farklı kimyasal bileşimlere sahip Alüminyum alaşımlarının tane inceltme ve modifikasyon işlemlerine tepkileri değişkenlik göstermektedir. Bu çalışmada Etial standardı 110, 140, 160, 177 alüminyum alaşımlarının ilavesiz olarak, Al5Ti1B tane inceltici ilaveli ve Al10Sr modifiye edici ilaveli kum kalıba dökümünde mikroyapı özellikler üzerindeki değişim incelenmiştir. Çalışmada spektrometro ile kimyasal bileşim belirleme, mikro yapı incelemeleri gerçekleştirilmiştir. Deneyler sonucunda tane inceltici ilavesi ile alaşımlarda tane yapısının daha da inceldiği ve kaba dentirik yapısının bozunduğu tespit edilmiştir. Ayrıca modifiye edicinin etkisinin yapı içerisindeki Ötektik Si içeriğine bağlı olarak olumlu yönde değiştiği anlaşılmıştır.

  AtıfOpenAlex6·TR Dizin4

  İncele