Condition-based maintenance model considering positive and negative maintenance effects for dependent competing failure processes

Generally, the states of the systems do get recovered after maintenance. However, due to some problems resulted from human errors, product design flaws, maintenance circumstances etc, some negative maintenance effects still remain in the practice. In this study, we develop a condition-based maintenance model for a system with two dependent failure processes: soft failure due to degradation and hard failure due to random shocks, by considering both positive maintenance effect and negative maintenance effect. The system is inspected at periodic time intervals, and the decision of an appropriate maintenance action (no action, preventive replacement or corrective replacement) is made based on real-time conditions of the system detected through the inspection. Positive maintenance effect induces the states of the systems do get recovered after replacement. We consider that the inspection is destructive and propose a new negative effect model for describing the impacts of inspection action. The inspection actions may increase the possibility of both Soft failure and hard failure, and model by increasing degradation rate and reducing the hard failure threshold value. The objective of condition-based maintenance model is to determine the optimal inspection interval and preventive threshold value that minimizes the expected long-run maintenance cost rate. Finally, a numerical example is illustrated to demonstrate the application of our maintenance model and policy.