L & T 1996: Repairable System Reliability

Failure rate and thus the reliability of hydraulic excavators working in the field, which were essentially repairable systems, were modeled and estimated. The repair mechanism of the excavator was to simply replace a failed component by a new one. Thus the component failure rates were modeled using independent renewal processes. A non-parametric Kaplan-Meier type analysis suggested three-parameter Weibull distributions for the inter-arrival times of these component renewal processes. The threshold parameters were estimated using a Bayesian technique and were assumed to be known thereafter. The scale and shape parameters were estimated using the method of Maximum Likelihood. Then with the aid of the renewal equation these MLE's were utilized to approximate the MLE's of the component and excavator failure rates. Standard errors were derived using the delta method.