Underwater wet welding (UWW) is applied to repair offshore structures, underwater pipelines, water transport, docks and harbour equipment. In this study, the mechanical and microstructural properties of AH36 low carbon steel were investigated at different welding current strengths and different seawater temperatures using metal arc welding (SMAW), an underwater wet welding method. Changing seawater temperatures and welding current parameters were examined together, so that the change of seasonal variability in welding parameters and chemical structure of seawater was examined. For this purpose, in the first stage, the yield strength value of AH36 was statistically modelled using the central composite design with the response surface method with input parameters of seawater temperature (in the range of 9.7°C-25.3°C) and source current value (in the range of 49A-90A) and the best conditions were found as Optimum Yield stregth 270MPa, 17.5°C seawater temperature and 69.5 A source current value. In the second stage of the study, the data obtained from the optimisation studies were used in the multi-response optimisation model to obtain elemental exchange equations for Cr (R2 = 87.3), Ni (R2 = 64.45) and Mn (R2 = 65.74) ionised in seawater. Accordingly, it was observed that the change in Cr content in seawater is affected by source current intensity, Ni content is affected by seawater temperature and Mn content is affected by current intensity and seawater temperature together. ICPMS was used for ion exchange in seawater, EDS point analysis for chemical composition in AH36 and SEM for microstructure analysis.
Bu çalışmanın amacı standartlarda dövme malzemelerin ultrasonik muayenesi için izin verilen farklı frekanstaki ve çaptaki probların tren tekerlekleri üzerinde uygulanabilirliğini araştırarak hassasiyetlerinin karşılaştırmasının yapılmasıdır. Demiryollarında hareketli araçlar içerisinde kritik bir öneme sahip olan tren tekerleği ve akslarının tahribatsız muayenesi günümüzde büyük önem kazanmıştır. Tahribatsız muayene yöntemlerinin de gelişmesi ile birlikte uygulanabilirlik çok daha kolay bir hal almıştır. Demiryollarında işletme güvenliği açısından oluşabilecek süreksizliklerin önceden tespit edilmesi bu bakımdan çok daha kolaylaşmış ve olası hataların tahmini daha mümkün hale gelmiştir. Yüzeysel kusurların bulunması için genellikle manyetik parçacık muayene yöntemi tercih edilirken hacimsel kusurların bulunmasında ise ultrasonik muayene yöntemi ön plana çıkmıştır. Ultrasonik yöntemle muayene de ülkelerin standartları, malzemenin yapısı, imalat yöntemi, muayene tekniği gibi bazı temel parametreler referans olarak kabul edilmektedir. Demiryolları içinde bu durum geçerli olmakla birlikte bu çalışmada; ultrasonik muayenede genel olarak kullanılan prob frekansı ve prob çaplarındaki değişimin demiryolu tekerlekleri özelinde ölçüm hassasiyetine etkisi araştırıldı. Çalışmada 1MHz, 2MHz frekanslar ve 6mm ile 10mm çap değerlerinin çapraz kombinasyonları şeklinde deneyler gerçekleştirildi. Çalışma sonucunda probların ürettiği ultrasonik ses saçılımı ile frekans değeri arasında ters orantı bulunduğu tespit edilmiş olup daha yüksek frekanstaki probların daha az saçılım değerleri ile yüksek performans gösterdiği belirlendi.
The aim of this study is to investigate the relationship between the pulse echo value of the probes used in the ultrasonic examination method. Ultrasonic inspection method is known as one of the non-destructive inspection methods. Thanks to this method, discontinuities in the material can be detected without damaging the material to be examined. It works with the principle of sending the sound waves produced by piezoelectric materials to the material surface and reading the sound waves coming reversibly. As the general working principle, sound frequencies are used in the ranges that the human ear cannot hear. These frequency values vary according to the structure of the material and the environment to be examined, but generally vary between 1MHz and 4MHz. In our study, train wheels were preferred as material. Train wheels are produced from medium carbon steel material by forging method. Inspections of train wheels, which are exposed to dynamic stresses during operation, are of great importance. The method of drilling holes on the train wheels with 3mm artificial errors were created. Inspection was carried out with total probes with 3 different diameters and 3 different frequency values on the train wheels on which artificial defects were found. A spring mechanism has been prepared for the probes to contact the material surface with the same pressure force. Experimental groups and a data set was created of 9 tests were carried out with 6 different. The sound waves given from the probes were recorded as db unit. Although the frequency of the probes is seen as the basic parameter in the selection of probes in the literature, it has been observed that different probe diameters have an effect on the inspection sensitivity. IBk algorithm was used to determine the relationship between probe diameters and incoming sound waves. This algorithm is based on the principle of classifying objects based on the closest training examples in the feature space. In the model made using the IBk algorithm, a high correlation of 89% was found in the probe diameter and pulse echo value. This value is important in terms of showing the relationship between the probe diameters, which cannot be considered as the main parameter, and the pulse echo value.
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