A new imperfect maintenance model based on delay-time concepts for single components with multiple failure modes

Components with multiple failure modes may encounter imperfect preventive maintenance triggered by inspections during their two-stage failure. Employing delay-time concepts and accumulative age, a new imperfect-maintenance model for these components is presented under the assumptions that failure modes are independent of each other and all kinds of defects will be dealt with in each maintenance task. Reliability and cost models are derived. Their characteristics are analyzed in numerical simulations. The results show components with more failure modes and worse imperfect inspection maintenance will have lower reliability, lower expected cycle cost and higher average cost per unit time. With an increasing inspection interval, the cycle cost will monotonically decrease while the average cost per unit time may have a local minimum. If inspection maintenance is insufficient, the minimum of the average cost per unit time will disappear, as does the best inspection interval.