Classes of imperfect repair models based on reduction of failure intensity or virtual age

This paper proposes two new classes of imperfect repair models. The failure process without repair is supposed to be a Non Homogeneous Poisson Process (NHPP). The repair e ect is characterized by the change induced on the failure intensity before and after failure. In the rst class of models, repair e ect is expressed by a reduction of failure intensity. In the second class, repair e ect is expressed by a reduction of the system virtual age. In each case, several particular cases are studied, which take into account the possibility of a markovian memory property. For almost every model studied, there exists a minimal wear intensity, i.e. a maximal lower bound for failure intensity. The classi cation presented here involves existing models and allows the proposition of new ones. The models are compared in terms of wear-out speed. Finally, a numerical statistical study on the quality of the model parameters estimators is presented.