Loads and stresses—the real cause of failures in surface mining machinery

Conclusions

On large mining machines, most failures are initiated by fatigue. In many failures the material properties are considered satisfactory, and the root cause of the failure lies in the loads, stresses, and high number of cycles. Final failure occurs when the combination of nominal, dynamic, and residual stress exceeds the capacity of the component. Determining all the possible loads and resulting stresses in the component or structure, if necessary by measurement, is fundamental to the failure investigation process. Similarly, engineers designing solutions need to understand the interaction between stresses and material properties in order to achieve successful outcomes.

Failure of components that have been in service for what would normally be regarded as a satisfactory life can still be very costly due to consequential damage and loss of production.

When decisions are made to continue operating damaged equipment, the potential failure modes need to be analyzed and understood. Stresses in components can exceed those due to the nominal loads. Fabrication methods (residual stresses), misalignment, and unexpected loads (such as torsional dynamics) can result in reduced tolerance to damage and potentially catastrophic failure.