Mathematical model of reusability

Recently the reuse of products or their components has been recognized as an effective way to reduce solid waste and to conserve natural resources. To decide whether a product or its component should be reused or not, we need to evaluate its reusability adequately. In this paper, as a criterion for the evaluation, the authors define and model the reusabilities of a product and its component, based on reliability theory. The authors define the reusability of a component as a probability that a product having been used for a time period ends its life but a component included in it is reusable. Based on the definition, the authors develop a mathematical model of reusability, which is a function of use time. The authors made several graphs of the mathematical model, with changing values for parameters such as shape parameter of Weibull distribution. As a result, it is found that the reusability of a component dose not always decrease as the use time is lengthened. This is interesting because it goes against general impression that the reusability decreases as the use time is lengthened. Next the authors define and model the reusabilities of a product and a unit. The authors believe that the models of reusabilities are useful for deciding whether a product or its component should be reused or not and the models may be used for production management for reuse and remanufacturing.