Modeling Remaining Useful Life Dynamics in Reliability Engineering

A Review of Modeling Remaining Useful Life Dynamics in Reliability Engineering Pierre Dersin CRC Press, 2023 In my opinion, this is a very important addition to our reliability engineering technology. It provides a comprehensive and definitive treatment of the modeling of remaining asset life. More significantly, the construction is new, insightful and broadly applicable. This book should become a part of every reliability engineer’s reference library. The key and very significant contribution of the text is that the author shows that the remaining useful life of an asset can be modeled using a linear or a piecewise linear function of time or in some cases of a transformed time scale. The author specifically shows that this feature of the residual life occurs in all of the most commonly used probability models of life duration. He shows that the (piecewise) linear relationship occurs for exponential, uniform, Dirac, Weibull, Lognormal, Pareto and Gamma life distributions and also for gamma process and Weiner process degradation models. In each case, he shows the mapping from the life distribution parameters to the (piecewise) linear remaining life models. In addition, he constructs the time scale transform for those distributions where it is needed. The result is an analytical framework for obtaining a residual life measure that can be the basis for efficient maintenance planning – especially for predictive maintenance planning. The text is well organized and provides complete explanations of the analytical details. The author starts with definitions of Remaining Useful Life (RUL), the Mean Residual Life (MRL) which is the expected value of the RUL and the “RUL loss rate” which is the derivative of the RUL and characterizes the ongoing evolution of the RUL. He then establishes the general relationship between the MRL and the reliability function. This relationship forms the basis for the RUL analyses that follow and these analyses are also substantial. The continuing constructions, include the definition of confidence intervals for the RUL, the parametric definition of the linear time functions for the MRL, the coefficient of variation for the RUL and the determination of the relationship between the confidence interval for the RUL and the RUL Loss rate. Following an excursion into moment generating functions and cumulative hazard functions, the author generalizes the previous results to MRL measures that are piecewise linear functions of time. Once this generalization is established, the author defines the non-linear time transformation that allows the MRL for most life distributions to be expressed as piecewise linear functions. He specifically shows the construction for several cases in which commonly used life distributions and also to degradation models. The author devotes a complete chapter to the examination of the properties of the time transformation that allows for the linearization of the MRL based on so many commonly used life duration models. This assures that the reader has a full view of the power of the analysis that has been presented. At this point, the analytical construction is really complete. Nevertheless, the author continues further to show the applicability of the method to cases of multiple failure modes and he then addresses statistical estimation methods. As part of this treatment, he explains the possibility of using Bayesian estimation strategies in the analysis. He completes the text with a discussion of maintenance planning models and methods and with a suggestion of where ongoing research seems appropriate. These discussions are insightful and useful but in my view, the exciting feature of this text is that the treatment of RUL is so thorough that the results developed will support the formulation of predictive maintenance strategies. I think that every reliability engineer that is working with asset management questions should read this text and use it as a basis for using asset monitoring information to define efficient adaptive maintenance plans. In closing, I suggest that this text will become one of the classic standard references for reliability engineers. Joel A. Nachlas, Ph. D.