Reliability allocation principle for large scale system

For a large scale series mechanical system composed of a great number of components, the component reliabilities allocated according to classical system reliability model are usually unrealistically high, even though the assigned target reliability for the system is quite low. Generally, system reliability can not be calculated from component reliabilities owing to the dependence among component failures. For the same reason, system reliability can not be simply allocated to the individual components according to traditional system reliability model. Based on comprehensive analysis to the controlling factors of component failure dependence, the present paper introduces new definition of system complexity and component complexity, presents load roughness based principle for system reliability allocation. According to such a principle, system reliability requirement can be reasonably allocated to components.