On time-dependent availability and maintenance optimization of standby units under various maintenance policies

The time-dependent unavailability of periodically tested aging components is studied under various testing and repair policies in which component renewals may or may not take place in tests and/or repairs. Cost functions are developed under the conditions of three different preventive maintenance policies, including the costs of testing, maintenance, repairs and accidents. Criteria and equations are developed for the economic optimization of two time intervals, one for periodic testing one for scheduled maintenance. Optimization is based on the average cost rate, with and without an additional constraint for the maximum accident rate. The roles of different costs and aging parameters are visible in the explicit results obtained for several models, most generally in the case of an extended Weibull hazard rate. (C) 1997 Elsevier Science Limited.