Graphical analysis of ill-collected interval data for a repairable system in vehicles

A nonparametric graphical method based on the mean cumulative repair function (MCRF) concept is developed to interpret ill-collected interval data of a repairable system. The data contain only the number of units put into the field per month and the number of repairs per month. No tracking of the history of each individual system is available, and no information on the number of systems removed from the field is recorded. The graphical method provides useful engineering insight into the system. The benefit of using this graphical method as a tool to compare the original product design with redesign, if elimination of certain failure modes can be accomplished, is shown. A parametric approach which fits a nonhomogeneous Poisson process (NHPP) model to the graphical results is briefly discussed