Delay Time Model Based on Imperfect Maintenance

The influence of imperfect maintenance on failure process has not been considered in the delay time model(DTM).Introducing the concept of proportional age reduction model,an improved DTM is proposed.It is assumed that the inspection maintenance is imperfect while the failure maintenance is perfect.Imperfect maintenance affects the instantaneous rates of defect and failure.The long-run average cost per unit time is derived from the assumptions.The numerical examples show that the imperfect maintenance heightens the long-run average cost per unit time,and an optimal inspection interval of cost minimization exists if the inspection maintenance is near to perfect maintenance,while the optimal interval disappears if the improvement factor decreases enough.