FAILURE ANALYSIS OF MACHINE SHAFTS

Whether related to motors, pumps or any other types of industrial machinery, shaft failure analysis is frequently misunderstood, and often being perceived as difficult and expensive. Analysis should be relatively straight forward in most most machine shafts, however, since the failure typically provides strong clues to the type and magnitude of forces acting on the shaft and the direction they acted in. The failed part can therefore tell exactly what happened. At this point, it's also necessary to say that caution on interpreting the clues needs to be taken, while the oldest part of a fatigue failure typically has the smoothest surface on at least 98% of the time – it's still crucial to look carefully at the failed part in the area of the origin. The shaft surface will describe the force. A crack always grows perpendicular to the plane of maximum stress. Therefore, if we can determine the plane of maximum and minimum quality conditions of the shaft surface, we then can evaluate the most and least resistance to failure, which can be used to determine the reliability and life of the shaft as well as its original and final shaft surface conditions. Many times, we've seen shafts where the originating force was torsion with a sort of angular cracks, but the majority of crack propagation was in bending – fooling inspectors into thinking that bending was primary force. At this point, it is interesting to note that, it is a good thing to determine the maximum and minimum shaft surface conditions, but quite better to determine the conditions in between, which will help to know the reliability/life growth and degradation of shaft. The knowledge of the maximum, minimum and real-time points of shaft conditions will help to determine control limits, threshold , and failure points. Technological Inheritance Coefficients can be used to assess the operating conditions and performance of shafts, since technological inheritance is the transfer of the properties of object (e.g the shaft quality and process effectiveness parameters) from its initial to final operation of a technological system. Technological Inheritance Model can therefore be used to determine maximum and minimum reliability/life, reliability/life growth and degradation, threshold points and failures of shafts as well as to evaluate the effectiveness/efficiency of the process. The Knowledge of Reliability growth can be used to assess the optimum reliability of shaft for the best selection and purchase of shafts and equipment as well as knowing the Reliability degradation can be used to assess the failures of shafts and equipment. Real-Time Reliability/Effectiveness growth and degradation test during operation will definitely lead to a sustainable development in design, manufacturing, operation and maintenance.