A study on optimal age replacement of dozer engines

In this paper, the concepts and methods of total time on test (TTT) plots are discussed. The failure data of two groups of electro-mechanical equipment (indigenous and imported dozer engines) are used to draw TTT plots, which indicate health of equipment in terms of failure rate. The optimum replacement interval is obtained for the equipment with increasing failure rate depending on the type of the data i.e. independently and identically distributed (i.i.d) or not. Graphical and analytical tests are used to confirm the nature and trend of the data. Non-parametric methods like Kaplan-Meir estimate and Nelson estimate are used to evaluate cumulative distribution function and scaled TTT to construct the plots. Parametric methods like Weibull and power law process models are used to verify the graphical results.