Age Replacement Models with Constant and Random Replacement Times

Preventive replacement policy conducted at a routine time [Formula: see text] has been surveyed extensively in literatures. Another two random replacement times [Formula: see text] and [Formula: see text] for time [Formula: see text] are jointly considered in this paper. We formulate the models of replacement first, replacement last and replacement middle, which are based on the respective assumptions of whichever occurs first, whichever occurs last and whichever occurs middle. Next, we modify replacement first and replacement last by using whichever occurs first and last jointly. Furthermore, we give the model of replacement overtime when the assumptions of whichever occurs first, whichever occurs last and replacing the unit over time [Formula: see text] are simultaneously considered. Comparisons among these replacement models are made to find which policy is more economical than the other.