Sequential imperfect preventive maintenance models with two categories of failure modes

In this paper, we introduce the concept of two categories of failure modes: maintainable failure modes and nonmaintainable failure modes into the mode ling of preventive maintenance IPM) activities. The hybrid model proposed b y Lin et al. is used to model the effect of a PM activity on the failure ra te function of maintainable failure modes. However, PM does not change the hazard rate function of nonmaintainable failure modes. PM is performed at a sequence of intervals. The objective is to determine the optimal PM schedu les to minimize the mean cost rate. Numerical examples for Weibull hazard r ates ate given. (C) 2001 John Wiley & Sons, Inc.