PSI - Issue 58

Włodzimierz Dudziński et al. / Procedia Structural Integrity 58 (2024) 54 – 60 W. Dudzi ń ski et al. / Structural Integrity Procedia 00 (2019) 000–000

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As a result of the calculations, highly stressed areas were identified. Due to the high level of stress values obtained (1280 MPa), the calculations were carried out for two variants of material characteristics: - linear elastic material (Fig. 11) - non-linear, elastic-plastic material, consistent with verification tests (Fig. 12)

Fig. 11. Stress plot in MPa - linear elastic material.

Fig. 12. Stress plot in MPa – non-linear, elastic-plastic material.

5. Conclusion In the article failure analysis of the discharge boom suspension was presented. During operation of the excavator, damaged of the axle occurred. Failure of this element caused uncontrolled movement of the discharge boom according to the direction of gravity. Analysis of the fracture and material indicated possible reasons of the failure. Fracture of the broken cross section is mainly due to fatigue with well-visible slip bands. Only 20% of the section is the rupture zone, which means that the static safety factor is about 5. The origin point of the fatigue fracture is located next to the notch axle surface in the area (change of the cross section). Verification of the material microstructure showed that there is an undesirable ferrite acicular structure with features of the Widmanstätten pattern. Such a structure is not suitable for currying structural elements subjected to high loads, because of its sensitivity to initiation and propagation of the fatigue crack. Strength analysis of the axle was prepared with the use of FEM. The results of this analysis showed that the maximal values of the von Misses stresses were located in the notch of the axle. This value was equal to 471 MPa in the case of elastic plastic material. Such value, that changes during excavator operation, in connection with the notch effect and insufficient material microstructure, caused failure of the axle and as a consequence the discharge boom of the excavator. Finally it can be stated that presented serious failure was caused by fatigue fracture. It was because of combination of three factors important in case of fatigue crack initiation and propagation. These