Cost Functions for Systems with Spare Components

Cost functions for determining the optimum number of spare elements to be assigned to systems of identical components under a certain replacement scheme are investigated. The properties of one cost function are studied for component life as an exponentially distributed random variable, and tables are presented of the number of spare components that minimize the function for specified cost ratios. The problem of the optimum number of spares is also considered for systems in which unfailed components may be salvaged for use with later systems.