Spares are commonly used to improve system performances. They are allocated to original components in parallel during system missions. Various methods for finding optimal allocations have been proposed in the literature. The optimal configurations depend on system structures and component lifetimes. For sake of brevity, lifetimes of components are commonly assumed to be independent. This paper deals with systems when component lifetimes are dependent and heterogeneous. Moreover, the spare is also allowed to switch among original components in order to impose more flexibility for spare management. Explicit expressions for system reliability functions are derived in details. Since system lifetimes are random phenomena, stochastic orders are utilized for comparison purposes. various illustrative examples are also given.

Keywords