A condition-based maintenance for a system subject to multiple degradation processes and external shocks

This paper analyses a condition-based maintenance for a system subject to different competing failure modes: internal degradation and external shocks. Internal degradation is the result of the arrival to the system of multiple cracks that grow according to stochastic deterioration processes. External shocks arrive to the system at random times and provoke the system failure. A condition-based maintenance model with periodic inspection times is developed for this competing failure model. Under this maintenance strategy, a preventive replacement is performed when the degradation level of a given crack in an inspection time exceeds a predetermined threshold. A corrective replacement is performed when the system is failed in an inspection time. Under this maintenance scheme, the expression of the expected cost rate is obtained. A numerical example illustrates the maintenance model.