Assessment of the weld root fatigue of a hydraulic cylinder

This thesis deals with the theories used to study the fatigue life of weld joints with a major focus on the method of P. Dong. Especially the weld root fatigue is analysed first with some simulation, supported by the use of FEA, and after with a real study case. The purposes of all this study is in a first place make a review, off all the method, a comparison between the most common and the latest one, study the stress linearization proposed from P. Dong to assess the strength fatigue in the root of welded joint, and so discover the advantages of using this approach. In second place the latest version of the method was applied to study the root fatigue failure of a cylinder used to lift weight on a forklift truck. The assessment of the cylinder’s failure wasn’t giving good results using the hot spot method, so the real behavior of the structure was not really captured and it can be an issue in the mechanical fatigue design. On the other side the Dong’s approach, after long test and studies, was providing results close to the real behavior of the cylinder in terms of fatigue life strength.