Abstract

Fatigue testing of tubular joints is normally performed at a low frequency, making the tests typically very long. Recently, a new testing method has been developed where a specimen is excited close to its resonance frequency, making it possible to achieve testing frequencies higher than 20Hz. In the present investigations, different nodes representing an X-joint (diameter of the brace 711mm, wall thickness 20mm) were tested until failure in the resonance test set-up. The new testing method allows to load the full circumference of the weld with a nominal stress following an elliptic profile, such that the fatigue cracks can be initiated at many locations around the weld with similar probability of failure. The paper will present the strategy for the design of the specimen, aiming to achieve similar resonance frequencies for in-plane and out-of-plane bending and similar probability of failure along the welds. After reception of the specimen and testing, new finite element simulations were run and compared to the experimental response of the specimen. The influence of different aspect of the modelling will be discussed, with their influence on the identified resonance frequency and strain gauge readings. The investigation proves that it is possible to obtain a reasonably homogeneous hot spot values along the weld, resulting in the initiation of cracks not anymore dictated by the hot spot values, but by the local geometry of the weld.

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