Root cause assessment of welded satellite gear carrier failure in a bucket wheel excavator

Abstract

In this study was investigated the fracture of the welded supporting structure of a satellite carrier of a bucket wheel excavator drive reducer. The research was aimed at identifying the root causes of the failure through an integrated failure analysis combining theoretical calculations, numerical modelling and experimental investigations. The loading analysis included digging resistance, natural and forced oscillations of the excavator structure, and verification of the support strength under variable operating conditions. Finite element analysis was used to determine the stress state in the critical regions of the carrier, while the field measurements were performed to assess operational stresses and vibration be-havior under different excavation regimes. In addition, metallographic and scanning electron micros-copy examinations were carried out to identify the fracture features and weld imperfections. The re-sults showed that the critical sections of the support structure operated under stresses close to the yield limit, while impact loads and low-frequency oscillations significantly increased the risk of failure. Fractographic observations revealed lamellar tearing, low-cycle fatigue features and a heterogeneous weld structure containing cracks, inclusions and gas porosity. The fracture was therefore caused by the combined effect of excessive service loads, dynamic excitation, stress concentration and imperfec-tions in welded joints, which should be more comprehensively considered in the design and assessment of such structures.