Browsing by Author "Karakas, Ozler"

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Citation - WoS: 4
Citation - Scopus: 4
The Influence of Corrosion on the Mechanical Behavior of Aisi 316l Stainless Steel Welds
(Kaunas Univ Technol, 2019) Turkan, Murat; Karakas, Ozler
Stainless steels are widely used because they have high corrosion resistance. However, they can also suffer corrosion due to the constant aggressive effect of the environment or due to chemical and physical malfunctions. It is of great importance to determine the behavior of welded austenitic stainless steels in corrosive environments for safer construction. For this reason, in this study, the corrosion and mechanical behavior of welded austenitic stainless steels exposed to salt spray was investigated. In the first stage, commercially available AISI 316L austenitic stainless steel materials with 4 mm thickness were joined with the TIG welding method, both with and without filler metal. To specify the structure of the weld zone, the micro-macrostructure and micro hardness values of the welded samples were examined before the salt spray experiments. The salt spray test was performed in compliance with the EN ISO 9227 Corrosion test in artificial environments standard, in which the tensile samples of welded AISI 316L materials were subjected to salt spray test up to 1000 hours. Tensile tests were carried out following salt spray tests.
Citation - WoS: 34
Citation - Scopus: 40
Numerical Modeling of Defect Formation in Friction Stir Welding
(Elsevier, 2022) Turkan, Murat; Karakas, Ozler
This study presents an investigation of welding defect formation in joining AZ61 magnesium alloy with friction stir welding by means of a 3D finite element model. The numerical model was created and analyzed in the ABAQUS software. This numerical model uses coupled Eulerian Lagrangian formulation, modified Coulomb's friction law, Johnson-Cook material law, mass scaling technique, and temperature dependent friction coefficient values. The numerical model was validated with experimental results in terms of heat input, temperature dis-tribution, plastic deformation type-amount, and weld defect formation in the weld zone. In friction stir welding, the heat input with a certain tool simply changes directly proportional to the ratio of tool rotation speed to tool feed rate for constant tool compressive force. In the numerical model, as in the experimental study, when the ratio of tool rotational speed to tool feed rate is 2, low heat input results in insufficient plastic deformation, leading to the formation of weld defects in the form of void. When the ratio of tool rotational speed to tool feed rate is 3, however, it was observed that sufficient heat input is provided, and no welding defects occur. The generated numerical model enables the determination of the welding defects that occur in the form of voids in the friction stir welding in a very short processing time. Besides, weld seam geometry can be predicted quite accurately with this model.
Citation - WoS: 17
Citation - Scopus: 21
Two Different Finite Element Models Investigation of the Plunge Stage in Joining Az31b Magnesium Alloy With Friction Stir Welding
(Springer International Publishing Ag, 2021) Turkan, Murat; Karakas, Ozler
This study presents an investigation of the plunge stage in joining AZ31B magnesium alloy with friction stir welding using two different 3D finite element models based on Arbitrary Lagrangian-Eulerian formulation and Coupled Eulerian-Lagrangian formulation. The investigations are made with the ABAQUS program. Johnson-Cook plastic material law and Coulomb friction law are used in both models. Models are compared in terms of temperature, strain distribution, and processing time. In both models, very similar temperature and strain distributions are obtained in the weld zone and the models are validated by experimental results. In addition, with the increase in the rotational speed of the tool, temperature and strain in the welding zone increase similarly in both models. In the model using the Arbitrary Lagrangian-Eulerian formulation, mesh distortions occur when high mesh density is not created in the plunge zone. No problems related to mesh distortion are encountered in the model using Coupled Eulerian-Lagrangian formulation. Moreover, it is found that the model using the Coupled Eulerian-Lagrangian formulation has a lower processing time and this processing time is not affected by the rotational speed of the tool.