Some problems on the selection of a condition based maintenance technique for mechanical systems

• In the first paper we focused mainly on establishing a sequential method for the selection of a maintenance technique for mechanical systems. The selection problem is studied for the components having considerable consequences and a non-negligible failure intensity. Identification of these components based on their failure mechanisms and failure causes is discussed and a modified version of the usual Failure Modes, Effects and Criticality Analysis, FMECA is suggested. A cumulative sum chart is proposed to identify a replacement time. This is explained by way of two examples. In order to run cost per unit time is proposed. The selection of a maintenance technique based on the intrinsic information of monitoring parameters is introduced.Ability of a monitoring parameter in predicting failures, can be described as a probability of failure in the future conditionally on the current value of a model monitoring parameter. Thus, the second paper is focused on introducing a model relating a condition dependent failure rate to a component condition. For the selection of a cost-effective technique a modified proportional hazards model, PHM, is proposed. The modified model is able to reveal the effect of observing monitoring parameters and operating conditions on failure rate function.A graphical method, based on a Generalized Total Time on Test, a GTTT- plot, for the selection of a cost-effective technique is proposed in the third paper. Also, a graphical method to estimate the threshold level for a cost-effective technique based on the same concept is suggested. These methods are illustrated by way of an example.

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