Abstract
This paper proposes random age, periodic and block replacement policies which are made at random variable times, and optimal policies that minimize their expected cost rates are discussed analytically and computed numerically. We compare such random replacements with their standard policies that are made at constant times. Comparison results show that when costs for random and constant replacements are the same, the standard policies are better than the random ones. Furthermore, it is computed numerically that if how much the random replacement cost is lower than that for the constant one, then the standard and random replacements have the same optimal cost rates. That is, the modified random replacement costs and their optimal times are discussed and computed when the random replacements would be better than the standard policies.
