Kaynaklı çelik yapıların sayısal olarak yorulma dayanımlarının belirlenmesi

Fatigue of metals has been an area of mechanical sciences that yet has not been completely well understood. There has been much research and many studies about mechanical behavior of fatigue evaluation of metals. Besides this, fatigue of welded components is even more complex. Apart from the thermal cycles during welding, which enormously affect the base material and introduce residual stresses and distortion to the weld zone, the fusion process of filler leads to very heterogeneous micro structures, varying the materials' mechanical properties and chemical composition throughout the neighbouring area of the joint. Moreover, weld defects like porosity, slag inclusions, undercuts and overlap, among others, can significantly reduce the fatigue strength. All these reasons create a proper environment for especially weld toe cracking, which is the most critical area of welding (strongly depends on the loading conditions). Based on identified source of problems, several improvement techniques have been developed and they have proven to increase the fatigue strength of welded area by inducing compressive stresses in weld toe, modifying the mechanical design into smoother geometries, modifying the welding techniques and processes, and similar. Fatigue mechanisms around the welded area of structures has been a major area of investigation for engineers especially for those working in the area of rail vehicle, automotive, naval and construction equipment industries. Mainly being initiated from these industries, many studies and codes have been developed for evaluating the fatigue conditions welded areas by both academic and industrial authorities. In this study, numerical fatigue strength assessment in welded areas were considered on a preferential basis according to internationally accepted codes, including FKM (Forschungkuratorium Maschinenbau), DVS 1612, and EuroCode 3 (EC3, EN-1993-1-9). Each of these international codes have their own assessment theory and technique for the fatigue strength assessment of welded structures. To be able to understand the fatigue behaviour in the welded areas, structural fatigue theories should have been well understood. In this study, stress-based fatigue analysis theory have been processed and implemented via numerical methods. Fatigue strength assessment of welded structures and evaluation of stresses in notched areas can be processed numerically either with manual calculations or commercial software packages. In this study, for fatigue stress assessment in welded areas a software package LIMIT 2015 was used in accordance with ABAQUS/Standard. It has been seen that; numerical methods can be used for strength assessment by comparing theoretical solutions to numerical outputs for different codes. Based on the specifically chosen examples, it can be concluded that, analysing the fatigue behaviour in welded areas has a strong relationship with the structural design process. To be able to increase the fatigue life of welded areas of the structure, it may be needed to alter the structural design in accordance with the fatigue behaviour in welded areas. Even statically safe and approved designs have to be fully analysed according to fatigue behaviour in their welded areas or joints.