Gazi University Journal of Science Part A: Engineering and Innovation, cilt.5, sa.2, ss.79-88, 2018 (Diğer Kurumların Hakemli Dergileri)
Machine parts fail to perform their tasks due to the fatigue with the rate of 90%. The fatigue applications have been known since the early days of the industrial revolution. The field of study on metal fatigue has started to expand due to the increase in the use of steel constructions in the systems of railway bridges in particular. It is of critical importance for all of the engineering fields to produce designs against the fatigue. Moreover, it is quite difficult to determine the initial damages of the fatigue by way of observation and the initial damages of the fatigue cannot be mostly recognized until a structural component becomes unusable. Therefore, the determination of fatigue life of the structural members during the stage of design and development results in a considerable decrease in unexpected damage risk that may occur during the use. Thus, reliable methods which can accurately predict the fatigue life are required. However, it is very difficult to find one single method to determine the fatigue life because of the presence of different loads and different designs. Finding a generally accepted and unified method which can accommodate to the desired condition removes difficulties in determining the fatigue life for each of the designs separately and facilitates the design process against the fatigue. The fatigue strength is normally found by means of Wöhler method. It is also called as the method of (S-N) curves. In this method, each of test parts which are completely same in terms of material, shape and the quality of surface are continually forced to the stress at different levels and the number of cycles with which the fracture occurs is determined.
In this study, a bending fatigue strength machine was designed in accordance with the method of Wöhler curve. A linear motor enabling a linear movement was used in the bending fatigue testing machine. The designed bending fatigue machine was different from the existing machines in terms of not occupying much area, noise being lower, non-requirement of the additional apparatus (strap, camshaft, etc.) as the movement is linear; determination of the force applied on the test sample directly in computer software and easiness of the measurement and obtaining data such as on which life number the test sample fractured.