PSI - Issue 19

Giovanni M. Teixeira et al. / Procedia Structural Integrity 19 (2019) 175–193 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The welded joints on the brake chamber support and on the lug that attaches it to the rear axle are the most vulnerable to fatigue failures as Fig. 15 shows. As these welded joints are subjected to random vibration on the field a robust fatigue method is required to deal with the dynamic and probabilistic aspects of designing welded components. The proposed method, as already mentioned, combines the Battelle structural stress method (Verity®) and the frequency domain approach (also known by the name of random vibration fatigue approach). The best way to verify the results (in the frequency domain) is by comparing the fatigue life results produced by Verity® in the time domain. With this aim the loadings were measured on the rear axle of a vehicle driving on stone tracks known as “Belgian Blocks”. These loads can safely be assumed stationary and ergodic for all purposes.

Fig. 15. a) Fatigue failures on the weld that connects lug and rear axle. b) Fatigue failures on the weld toe of a connecting bracket.

The finite element representation of the brake chamber is presented on Fig. 16. The base highlighted in the figure represents the master node where the acceleration histories in the three orthogonal directions X, Y and Z are known. The system is assumed to be LTI (Linear Time Invariant) where the modal superposition technique is valid. A typical viscous damping of 0.01 was adopted in all scenarios.

Fig. 16. FE representation of the brake chamber and supports.