A Thermodynamic Entropy Based Approach for Prognosis and Health Management

Data-driven stochastic and probabilistic methods that underlie reliability prediction and structural integrity assessment remain unchanged for decades. This paper provides a method to explain the Prognostics and Health Management (PHM) in terms of fundamental concepts of science within the irreversible thermodynamic framework. The common definition of damage, which is widely used to measure the reduction of reliability over time, is based on observable markers of damage at different geometric scales. Observable markers are typically based on evidences of any change in the physical or spatial properties or the materials, and exclude unobservable and highly localized damages. Thermodynamically, all forms of damage share a common characteristic: “energy dissipation”. Energy dissipation is a fundamental measure of irreversibility that within the context of non-equilibrium thermodynamics is quantified by “entropy generation”. The definition of damage in the context of thermodynamics allows for incorporation of all underlying dissipative processes including unobservable markers of damage. Using a theorem relating entropy generation to energy dissipation associated with damage producing failure mechanisms, this paper presents an approach that formally describes and measures the resulting damage. Having developed the approach to derive the damage over time, one could assess the health of structures and components subject to known degradation processes. This paper presents a prognostic approach on the basis of thermodynamically derived cumulative damage, whereby the thermodynamic entropy, as a broad measure of damage, is assessed.