The Effect of Crack Orientation on the Propagation of Cracks in Graphene Nanoplatelet Carbon Fiber-reinforced Epoxy Composites Using Digital Image Correlation

Tolga Topkaya 한국섬유공학회 2021 Fibers and polymers Vol.22 No.5

This study experimentally investigated the fracture behaviors of graphene nanoplatelet (GNP) carbon fiberreinforcedpolymer (CFRP) composites for varying amounts of GNP reinforcement, crack lengths and crack orientationangles. The specimens were subjected to tensile loading, and their fracture toughness values were determined with respect tomaximum damage load and crack length. To compare the results obtained from experimental data, the fracture toughnessvalues, strain distributions and crack tip opening displacements were determined by using a Digital Image Correlation (DIC)technique from images recorded during the tests. The results showed that increasing the amount of GNP increased thefracture toughness of specimens. On the other hand, increasing the crack orientation angle decreased the fracture toughness. Increasing the crack length increased the fracture toughness values for a crack orientation angle of 30 ° but decreased for acrack orientation angle of 90 °. DIC results were found to be compatible with the calculated results using crack length anddamage stress values.

A Comparative Study of AISC-360 and EC3 Strength Limit States

Cem Topkaya,Serkan Şahin 한국강구조학회 2011 International Journal of Steel Structures Vol.11 No.1

A study has been undertaken to evaluate the similarities and differences between the steel building design specifications used in the United States and Europe. Expressions for nominal strength presented in the AISC-360 Specification and the Eurocode 3 Specification were compared for fundamental limit states. In particular, rules for cross-section classification, tension members,compression members, I-shaped members subjected to flexure, I-shaped members subjected to shear, and fasteners were studied. Results of the investigation revealed that, in general, both specifications provide nominal capacities that are close to each other. Significant differences were reported for some limit states such as flexure in I-shaped members with non-compact flanges, shear and lateral torsional buckling in I-shaped members, and bearing strength at bolt holes. In this paper, the details of the comparative study are presented along with observations that are useful for practicing engineers

Investigation of low velocity impact behaviors of honeycomb sandwich composites

Tolga Topkaya,Murat Yavuz Solmaz 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.7

Honeycomb sandwich composites are used as significant structural members in advanced engineering applications. Thus, it is critical to determine how they behave under impact loading, in addition to other loads. In this study, low velocity impact loading behaviors of honeycomb sandwich composites were experimentally investigated. Almost all of the design parameters of honeycomb sandwich composites were investigated. The results indicated that the core thickness of honeycomb had no effect on the strength of the composite, and the parameter influencing the impact behavior of the specimen the most was the face sheet thickness. When the face sheet thickness of the specimen was increased, the most apparent strength increase was observed in the models using carbon fiber-reinforced composite face sheets. For all face sheet types subject to impact energy of 10 Joules, the upper face sheets of 0.5 mm-thick specimens were perforated.

Mechanical properties of fiber/graphene epoxy hybrid composites

Tolga Topkaya,Yahya Hışman Çelik,Erol Kilickap 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.11

The aim of this study is to determine the effect of graphene nanoparticle (GNP) reinforcement on the mechanical properties of glass fiber reinforced polymer (GFRP), carbon fiber reinforced polymer (CFRP) and aramid fiber reinforced polymer (AFRP) composites commonly used in the space and defense industry. Accordingly, GFRP, CFRP and AFRP composites were produced by using hot pressing method. In addition, hybrid fiber composites were produced by adding 0.1 %, 0.2 % and 0.3 % GNP to these fiber reinforced composites. The tensile strength and modulus of elasticity of the composites were determined. The tensile damage fracture regions were analyzed by scanning electron microscopy (SEM) and energy distribution spectrum (EDS). It was observed that the addition of 0.2 wt. % GNP to GFRP and CFRP composites increased tensile strength and modulus of elasticity. However, the addition of 0.2 wt. % GNP to AFRP composites had no effect on the tensile strength; on the contrary, it partially reduced the tensile strength but increased the modulus of elasticity. On the fracture damage surfaces of the GFRP and CFRP composites and the GNP/GFRP and GNP/CFRP hybrid composites, the fibers were completely separated. On the damage surfaces of AFRP composite and GNP/AFRP hybrid composites, the fibers were deformed but these fibers were not separated from each other. From the EDS analysis, it was observed that the element C increased in the composites with the addition of GNP to the fiber reinforced composites.

Design Overstrength of Steel Eccentrically Braced Frames

Ahmet Kuşyılmaz,Cem Topkaya 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.3

The paper reports an analytical study on the design overstrength of steel eccentrically braced frames (EBFs). The study aimed at examining the influence of geometrical factors and seismic hazard on the design overstrength of EBFs. Pursuant to this goal a computer program which facilitates EBF designs was developed. The algorithm of the program adopts the lightest uniform frame design and library of link-beam-brace sub-assemblages concepts. The design output from the program was compared with published solutions and the results indicate that the algorithm developed as a part of this study is capable of providing lighter framing solutions. A parametric study was conducted using the developed computer program. The results indicate that the frames considered in this study have on average higher overstrength values when compared with the codified value even without considering potential increases due to material overstrength and strain hardening. The design overstrength was found to be influenced primarily by the link length to bay width ratio and the bay width, and secondarily by the building height and seismic hazard level.

Improving the diagnosis of high grade and stage bladder cancer by detecting increased urinary calprotectin expression in tumor tissue and tumor-associated inflammatory response

Yusuf Sahin,Ugur Yucetas,Huseyin Aytaç Ates,Erkan Erkan,Esma Yucetas,Mustafa Zafer Temiz,Mahmut Gokhan Toktas,Mustafa Kadihasanoglu,Birsen Cigdem Topkaya 대한비뇨의학회 2019 Investigative and Clinical Urology Vol.60 No.5

Purpose: To investigate whether measurement of urinary calprotectin can serve as a biomarker in the diagnosis of primary bladder cancer and to confirm its diagnostic role in determining high grade and stage disease. Materials and Methods: Urinary calprotectin was measured in spot urine samples from patients with primary bladder cancer and control subjects. To confirm levels in urine, tissue samples were also obtained from bladder tumor and healthy trigone of bladder by transurethral resection in both groups. Finally, calprotectin levels in tissue and urine of the patients and control subjects were compared and their diagnostic potential was investigated in high grade and stage bladder cancers. Results: Of 82 participants, 52 were patients with bladder cancer and 30 were control subjects. The two groups were comparable in terms of age, smoking status, and comorbidities. Tissue and urinary calprotectin levels were significantly higher in the bladder cancer group. In subgroup analyses, urinary calprotectin levels were significantly higher in patients with high-grade, muscle-invasive tumors. After receiver operating characteristic analyses, the sensitivity and specificity of urinary calprotectin was 100% and 96.7%, respectively, in the diagnosis of primary bladder cancer. High grade and stage bladder cancers were detected with sensitivity and specificity of 70% and 74.2%, and 80% and 84.8%, respectively. Conclusions: Urinary calprotectin may be a valuable parameter in the diagnosis of primary bladder cancer with high sensitivity and specificity. Furthermore, it may be useful in the prediction of high grade and stage disease. However, more investigations are needed.