Table of Contents
Journal of Quality and Reliability Engineering
Volume 2013, Article ID 945039, 11 pages
Research Article

Differential Importance Measure for Components Subjected to Aging Phenomena

1NIER Ingegneria, Via Altabella 3, 40127 Bologna, Italy
2DIENCA, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy

Received 27 April 2013; Revised 2 August 2013; Accepted 19 August 2013

Academic Editor: Benoit Iung

Copyright © 2013 Stefano La Rovere et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The paper refers to the evaluation of the unavailability of systems made by repairable binary independent components subjected to aging phenomena. Exponential, exponential-linear, and Weibull distributions are assumed for the components failure times. We assume that components failure rate increases only slightly during the maintenance period, but we recognize the effectiveness of preventive maintenance only in presence of aging phenomena. Importance measures allow the ranking of the input variables. We propose analytical equations that allow the estimation of the first-order Differential Importance Measure (DIM) on the basis of the Birnbaum measures of components, under the hypothesis of uniform percentage changes of parameters. Without further information than that used for the estimation of “DIM for components,” “DIM for parameters” allows considering separately the importance of random failures, aging phenomena, and preventive and corrective maintenance. A two-step process is proposed for the system improvement, by increasing the components reliability and maintainability performance as much as possible (within the applicable technological limits) and then by optimizing preventive maintenance on them. Some examples taken from the scientific literature are solved in order to verify the correctness of the analytical equations and to show their use.