Maintenance models for a continuously degrading system

This paper considers on-condition maintenance of a continuously degrading system, in which the intermaintenance time and the maintenance time depend on the condition of the system at which maintenance is carried out. Without assuming any underlying statistical distribution of the time to failure, models are established to maximize the system average availability when the expected intermaintenance time and the expected maintenance time are (i) deterministic or (ii) contain random components. Optimal solutions on the condition of the system at which maintenance should be performed and the number of times of maintenance action to be carried out are obtained. Numerical searching procedures are proposed, and illustrative examples are given.