Optimal sampling-based sequential inspection and maintenance plans for a heterogeneous product with competing failure modes

Many products are stored for a long period of time before being used. Such products may experience on-shelf degradation and failure, and thus require repeated inspections and maintenances (IMs) to guarantee their reliability for future uses. However, for products with multiple failure modes, it may be economically impractical to inspect and maintain all the stored units with respect to all the failure modes. In this study, we propose and design dynamic sampling-based sequential IM plans for products that are subjected to competing failure modes during storage. The IM plans inspect a sample of stored units on their performance with respect to specific failure modes, followed by imperfect maintenance. The optimal IM plans aim to optimally balance the availability of heterogeneous units and the use of IM resources under flexible scenarios, by determining the (i) characteristics of the samples for inspections and (ii) product's maintenance and restoration thresholds. A numerical example on a type of airbag is provided to illustrate the efficiency of the proposed IM plans, and IM scenarios that should be employed under different circumstances are recommended.