A virtual age model based on a bathtub shaped initial intensity

This paper presents a new reliability model for complex repairable systems, which combines a bathtub shaped ageing and imperfect maintenance. A bathtub shaped initial intensity function allows to take into account the burn-in period, the useful life and wear out of the systems. Repair effect is expressed by a reduction of the system virtual age, which depends on the ageing of the system. The main characteristics of the model are derived. The most important one is that the maintenance efficiency allows an extension of the system useful life duration. A statistical analysis of the model and an application to real failure data are presented.