The optimization of repair decisions using life-cycle cost parameters

Life-cycle cost models typically minimize system repair costs as a function of various cost coefficients associated with a given repair option – such as discarding upon failure or repairing the components. Fixed costs such as set-up costs pose special problems for the minimization of life-cycle costs: first of all, fixed costs are characterized by step functions linked to capacity constraints, while variable costs are represented by continuous functions. Secondly, both categories of cost should be evaluated simultaneously for all components of a physical system and for all repair options. Thirdly, there are operational-research tools such as mixed integer programming which can solve large problems of this type under a set of acceptable simplifying assumptions. Heuristic methods can be used to minimize the search time for a global optimum solution. This paper describes an approach which has been successfully applied to maintenance planning, vibration analysis, and expert fault diagnostics. One of these applications is discussed in detail as an illustration of the method proposed.