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Analysis of fatigue damage accumulation of test specimens made from S690 and S960
Al Khazali, Mohammad ; Malíková, Lucie (referee) ; Seitl, Stanislav (advisor)
This thesis study and examines the behavior of high strength steels (HSS) during fatigue utilizing S-N curves of models based on the Palmgren-Miner Rule and some invented hypotheses, such as Haibach's model, Corten-Dolan's model and Serensen-Kogajev model. Firstly, a detailed mechanical testing will be done and discussed to ensure creating a proper understanding of the two types of steel that will be the focal point of the research. The curves created are interpolated using measured data form cyclically loaded of the steel to create the relation between the number of cycles the material can withstand before reaching failure state and the level of stress applied on a variety of specimens with different homogenizes but similar characteristics. The accuracy of each model is determined for each grade of steel, the S690 and the S960. Then we will conclude by the end of the work which can be considered suitable and which not of each model and an explanation of the reasoning behind the results achieved to ensure better outcome in future related work.
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Problems connected with the application of lamella flanges in steel bridge construction
Křístek, V. ; Kunrt, J. ; Škaloud, Miroslav ; Urushadze, Shota
Lamella flanges have lately grown very popular with the designers of steel bridges, because - in their belief - they provide us with the possibility of avoiding very thick flange plates in steel bridge structures. This belief is based on the assumption that the lamellas are perfectly plane and therefore, in perfect contact everywhere, so that the loading from one lamela is transmitted into other via pure compression, and that the perfect interaction of both lamellas is materialized by means of boundary fillet welds connecting both of the two lamellas. This simple assumption is, however, far from reality: it is not the means of steel fabricators, not even in the means of those which are very progressively equipped, to produce perfectly plane lamellas. Then both lamellass exhibit unavoidable initial curvatures, which in combination form a gap between the lamellas, and consequently the directly loaded lamela are pressed into this gap. As the loading acting on every bridge is many times repeated, the aforsaid phenomenon is also many times repeated, (we can say that the lamellas "breathe"), and then an unavoidable cumulative damage proces in the lamellas comes to being. The results of investigation will be described in the paper and thereby will demonstrate that the fatigue phenomenon accompanying the breathing of the lamellas can considerably limit the lifetime of the structure.
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