Age-based hybrid model for imperfect preventive maintenance

Several sequential Preventive Maintenance (PM) models for predetermined PM interval policies currently exist in the literature, however, much less effort has been devoted to age-based policies. The purpose of this paper is to develop a hybrid age-based model for imperfect PM involving maintainable and non-maintainable failure modes. The proposed hybrid model incorporates adjustment factors in both the hazard rate and effective age. PM is assumed to be imperfect. It reduces the age of the system and changes its hazard rate. The system undergoes a certain number of such PM actions before replacement. The problem is to determine the number of PM actions and the length of PM intervals that minimize the total long-term expected cost per unit time. Model analysis relating to the existence and uniqueness of optimal solutions is provided. Numerical examples are presented for illustrative purposes.