On the impact of undercuts and lack of penetration of cruciform joints from fatigue tests

Abstract

The assumption of the detail categories in EN1993-1-9 is the presence of a certain weld quality level. In order to find out the sensitivity of the resulting fatigue strength for cases where a worse or better quality level compared to the selected level of EN ISO 5817 is achieved, in this paper, special fatigue experiments are presented. The experiments refer to the load-carrying cruciform joint with lack of penetration and root fusion as well as undercuts. The performed fatigue investigations on cruciform joints are based on and accompanied by further fatigue test results of literature, documented in a detailed fatigue database containing 147 test series. Detailed information on mechanical properties, fabrication and metallurgical characteristics of the cruciform specimens are given. Extensive 3D laser scans of the specimens and ultrasonic testing as well as magnetic particle testing have been performed in order to analyse the imperfection sizes and scatters. The fatigue test results of the cruciform joints show, that undercuts lead to lower fatigue strength at the weld toe, as was to be expected. When reducing the fatigue resistance, undercuts could however be tolerated at secondary structural elements or marginally fatigue stressed components. A lack of penetration and/or root fusion can be tolerated, if the fatigue verification at the weld root is performed. A verification at the weld root can only be neglected in case of lack of penetration and/or root fusion, if the weld toe is decisive due to undercuts or large enough weld angels, here shown for 45°.