Fatigue behavior of different bracket connections

摘要

The paper presents fatigue tests with large scale models and analysis results of a European R&D project, called FatHTS. Tested were frame corners with three different bracket details: with symmetrical flange, with symmetrical flange and additional bracket nose modification, and with one-sided flange with sniped ends. In order to be able to make a comparison, the hot spot strain was determined by strain gauge measurements at all corners of each model. The FE results lead to higher hot spot strains and also the strain increases earlier in front of the hot spot. This is due to the different weld geometry in the drawing and in reality. In most cases the crack initiation did not occur as expected at the hot spot. The crack started at the root and propagated through the weld. Additional stress analyses revealed the cause of the unexpected crack behaviour. This was due to the fact that the weld carries the full load. The fatigue tests showed that it is difficult to predict the root failure in complex structures. The hot spot concept does not cover the metallurgical notch which occurs during fabrication. For toe failure good agreement is obtained between prediction and tests if the failure is defined as through-thickness crack.