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    Evaluation of the effect of MWCNT amount and dispersion on bending fatigue properties of non-crimp CFRP composites
    (Elsevier - Division Reed Elsevier India Pvt Ltd, 2022) Pekturk, Hatice Yakut; Elitas, Muhammed; Goktas, Mustafa; Demir, Bilge; Birhanu, Salih
    Multi-walled carbon nanotubes (MWCNTs) have many unique features that improve composite material properties, including a large surface area, thermal and chemical stability, and thermal and electrical conductivity. Our study aimed to examine the influence of MWCNT weight percentage on the fatigue characteristics of a polymer matrix composite strengthened with carbon fiber in fabric form. This study aimed to explore the additional properties and functions of these MWCNTs. For the experiments, MWCNTs were prepared by mixing them in solution with epoxy in three different weight percentages (0.5 %, 1.0%, and 1.5%) using a surfactant, and at 0.5 wt% without a surfactant. The prepared solutions were injected into four-axis non-crimp carbon fiber fabric plates via the vacuity mixture method and then cured for 48 h to produce nanocomposite plates. Using five types of composites, fatigue tests were carried out at six different amplitudes and a fixed frequency. Fatigue test specimens were subjected to detailed SEM analysis of their fatigue fracture surfaces. The investigational results revealed that the 0.5 wt% MWCNT epoxy solution had been homogeneously dispersed and exhibited the highest absorbance spectrum. The 0.5 wt% MWCNT specimen achieved the highest value in the fatigue life experiments. In addition, electron microscopy studies of the fracture surfaces of the test specimens determined that individual COOH-MWCNTs interrelated with the fibers and formed a bridge between fiber and matrix, whereas agglomerations caused weak bonding between the reinforcement fibers and matrix, making the material more brittle.(c) 2021 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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    Finite element modelling of the fatigue damage in an explosive welded Al-dual-phase steel
    (Walter De Gruyter Gmbh, 2023) Elitas, Muhammed; Goktas, Mustafa; Acarer, Mustafa; Demir, Bilge
    In this study, production of dual phase steel-Al 1100 aluminium alloy laminated composite by explosive welding and investigation the microstructural and mechanical properties especially fatigue life of the composite and its components were aimed. Finite element analysis (FEA) was used to simulate the bending fatigue tests of the Al 1100-DP steel (LITEC 1050) bimetal. A semi-wave at the explosive interface with intermetallic was obtained as a microstructural result. Hardness was increased near the interface due to deformation and intermetallic formation at the explosive weld interface. The impact test results showed that the samples' impact toughness was enriched by fabricating steel-Al laminated composite. The results also showed that the Al 1100-DP steel (LITEC 1050) bimetal composite properties were appropriate to the composite theory and satisfied strength-ductility relations accomplished. Additionally, the bending fatigue test and FEA results were compatible. Moreover, fatigue cracks were observed at the explosive weld interface between Litec DP steel and intermetallic but not at the Al-intermetallic interface.
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    An investigation on bending fatigue in a corrosive environment of dual-phase 1000 sheet steel RSW joints and damage model via experiment and numeric analysis
    (Sage Publications Ltd, 2024) Goktas, Mustafa; Demir, Bilge; Elitas, Muhammed
    Fatigue, corrosion, and fatigue damage models are best addressed to improve and understand the service performance of materials, particularly automotive steel. This study is an attempt to experimentally and finite element investigates plain bending fatigue performance and damage model of DP 1000 sheet steel resistance spot welding (RSW) joints in 3% NaCl aqueous corrosive treatment. RSW applications were carried out using different weld currents. The joint samples were then subjected to optical image analysis, tensile shear, and fatigue tests (3% NaCl-aqueous and normal atmosphere). A proper damage model of RSW junctions was developed and corrected by numeric analysis. Besides, RSW nugget formation, tensile shear, and plain bending fatigue tests were also applied. Consequence, fatigue behavior, tensile load carrying capacity, and effective fracture behavior of resistance spot welded joint specimens were evaluated. Results showed that a corrosive environment negatively affected fatigue performance. With the developed model, it was observed that the fatigue life of the samples decreased by 30-35% in the fatigue tests performed in the corrosive environment. Experimental and numerical analysis results of plain bending were compatible.