On the inescapability of aging in an imperfect preventive maintenance model

Segovia Garcia, Maria Del Carmen and Labeau, Pierre-Etienne; (2012) On the inescapability of aging in an imperfect preventive maintenance model. In: 11th International Probabilistic Safety Assessment and Management Conference and the Annual European Safety and Reliability Conference 2012. Curran Associates, Inc., pp. 287-296. ISBN 978-1-62276-436-5

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All systems are subject to aging and, given that, to the deterioration of their performances and ultimately to failure. Preventive maintenance actions attempt to restore the performances of a system or to keep them at an acceptable level, preventing its failure. In the literature, many models can be found that seek to embody the impact of the imperfect maintenance. Some of them focus on the concept of effective age: the effect of a maintenance action is expressed by means of a reduction in a fictitious age of the system. The effective age describes the present condition of the system and it is different from the calendar age, the time elapsed since the system was new. Classical models of this type (Kijima et at. (1988), Martorell et al. (1999), Doyen & Gaudoin, (2004)) assume maintenance brings a restoration proportional to either the age of the system before the maintenance, or the increase of age since the previous maintenance action. However, none of these models are fully satisfactory. In particular, they suppose independence between the efficiency of the maintenance action and the periods between interventions. Therefore, the resulting state of the system after maintenance is different for any modification in the maintenance period. Clavareau & Labeau (2009) and Labeau and Segovia (2011) introduced two new concepts: the maintenance elasticity: for limited delays in the realization of the preventive maintenance action the resulting degradation level of the system is the same; the inescapability of aging: even if a system is regularly and properly preventively maintained, its performance will unavoidably tend to decrease as a result of aging. This paper, deals with the modeling of the inescapability of aging, and its relation with the expected gain in mean residual lifetime brought by maintenance. We consider the natural variability of the problem in terms of the maintenance epochs, in the scheduling of the maintenance, and the resulting state of this maintenance.