A modified inspection model based on a two-stage failure process

A improved inspection model with two-stage degenerative process using inspection historical information and the concept of delaying time is proposed. The delay defect concept considers that the degenerative process of the system can be divided two stages: the normal working stage and the delay defect stage. DT is an experiential threshold time. So the delay defect stage is cut as non-severe defective and severe defective stage by DT. The system´s three operating state can be extended into four states, namely, normal, non-severe defective, severe defective, and fails states. Let us suppose that maintenance action is started if the system is inspected in a severe defective state after DT. However, difference maintenance actions are adopted if a non-severe defective state of the system is inspected before DT. We build the object function of the model to optimize the inspection cycle and value of DT. The model is illustrated through a case.