Mean Residual Lifetimes of Consecutive-k-out-of-n Systems

In this paper we study reliability properties of consecutive- k -out-of- n systems with exchangeable components. For 2 k ≦ n , we show that the reliability functions of these systems can be written as negative mixtures (i.e. mixtures with some negative weights) of two series (or parallel) systems. Some monotonicity and asymptotic properties for the mean residual lifetime function are obtained and some ordering properties between these systems are established. We prove that, under some assumptions, the mean residual lifetime function of the consecutive- k -out-of- n : G system (i.e. a system that functions if and only if at least k consecutive components function) is asymptotically equivalent to that of a series system with k components. When the components are independent and identically distributed, we show that consecutive- k -out-of- n systems are ordered in the likelihood ratio order and, hence, in the mean residual lifetime order, for 2 k ≦ n . However, we show that this is not necessarily true when the components are dependent.