Methodology of physical occurrences analogy in researching vehicle lifetime

Abstract

Lifetime as a critical dimension of the quality of a product is most often studied using the unreliability curve, when there are problems in determining the origin in terms of time limit (Delta t), since monitoring usually starts at one point in the lifetime and does not yield accurate data. Reliability theory cannot give satisfactory results, unless we can determine the effect of product care under conditions of use on malfunction and failure of parts, or of the entire system. Therefore, this paper introduces an original methodology for determining the lifetime of vehicles by applying the model of the physical occurrence analogy for fluid outflow from an open vessel. The analogy allows us to derive a formula for calculating lifetime, which does not require the extensive research necessary for reliability theory. This methodology is applied to data on passenger vehicles in the former West Germany, and to buses on the Serbian market. The lifetime of vehicles in West Germany had declined to 9.7 years by the end of the monitored period. The lifetime of buses in Serbia was 4 years until 1989, after 1990 it had risen to 8 years but it exhibits a tendency to decrease to 6-7 years soon. The model proposed in this paper yields good results that include the characteristics of maintenance done during the periods discussed. Our results should be verified in other areas as well.