‘Hot spot stress’ is an approach often used to consider fatigue loadings in heavily welded tubular joints. This article reports the determination of hot spot stresses in mining dragline booms, which are often ≥100 m in length, using strain gage measurements and finite element analysis (FEA) modeling as part of a structural health monitoring concept. Strain gages were installed on a typical A11 cluster for estimating hot spot stresses, as recommended in the existing fatigue design guidelines by the International Institute of Welding (IIW) and the International Committee for the Development and Study of Tubular Construction (CIDECT). The results from the experimental measurements and the FEA were found to be comparable to a large measure. It was concluded that while hot spot stresses were high enough at the weld toes to cause cracking, they could not explain the cracking that occurs at the welds in the main chords on their own. Issues in comparing theoretical and experimental measurements are discussed.
Failures in hoist and drag ropes are studied and described based on site inspections on Marion and BE draglines. Causes of the failures are discussed. Some of the analyses of the wire rope failures centres on the wire rope accessories through which these ropes travel during machine operation. The influence of wire quality on wire rope life is also studied. Visual and metallographic examinations are both used in this study leading to a better understanding of deterioration mechanisms that lead to failure of hoist and drag ropes under service loading.
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