Optimal repair policies with general degree of repair in two maintenance models

Two maintenance models for repairable systems with exponential lifetimes are studied. A maintenance strategy in the proposed framework specifies the degree of repair to be taken as a function of the virtual age of the system upon failure. In Model I we restrict attention to maintenance strategies in which only minimal or perfect repair can be employed upon failure. In Model II the degree of repair may vary. For some age-dependent cost functions, optimal maintenance strategies (minimizing the expected discounted costs over an infinite horizon) are determined analytically.