A multivariate CBM model with a random and time-dependent failure threshold

In a condition-based maintenance setting, the degradation of an item is usually represented by several condition variables, and they can be combined into a composite condition variable. In this case, the functional failure threshold associated with the composite condition variable is usually not a fixed and known constant. It is an open issue to model the failure threshold and accordingly determine a threshold of preventive maintenance (PM). This paper addresses this issue. The condition variables are combined using a weighted power model, the failure threshold is represented by the Gaussian process model, and the PM threshold is determined by two approaches. Based on the gamma process and stress-strength interference models, the distributions of time to failure and to the PM threshold are derived, respectively. The appropriateness of the approach is illustrated by a real-world example. (C) 2013 Elsevier Ltd. All rights reserved.