Availability and failure intensity under imperfect repair virtual age model

This paper develops analytical and numerical techniques to determine two important component characteristic, the failure intensity and the availability, when repairs reduce the virtual age of a unit. Finite repair times are taken into account. An exact Volterra integral equation and an approximate solution are provided for the intensity when component ages during operation and during repairs. A numerical technique is developed and illustrated for the alternative case, i.e. when ageing stops during repairs. The asymptotic behaviour is described in terms of two measures of the age-dependent expected time to the next failure.