Physics-informed machine learning in prognostics and health management: State of the art and challenges.

• Systematic bibliometric analysis of PIML in PHM. • Novel perspectives for PIML from the "Informed knowledge forms" and "Informed methods". • Taxonomy of PIML approaches in PHM. • Highlight remaining challenges and future perspectives based on this review. Prognostics and health management (PHM) plays a constructive role in the equipment's entire life health service. It has long benefited from intensive research into physics modeling and machine learning methods. However, in practice, the existing solutions often encounter difficulties caused by sparse data & incomplete system failure knowledge. Pure machine learning or physics-based methods can sometimes be infeasible in such situations. As a result, there has been a growing interest in developing physics-informed machine learning (PIML) models which allow incorporating different forms of physics knowledge at different positions of the machine learning pipeline. This combination provides significant assistance for detection, diagnostic, and prognostics. However, to the best of our knowledge, the bibliometrics analyses and the comprehensive review of the existing research concerning PIML in PHM remain vacant. Our review is therefore dedicated to filling these gaps. We synthesize the concept of PIML in PHM, and propose a taxonomy of PIML approaches from the perspective of "Expression forms of informed knowledge" and "Knowledge informed methods". The findings and discussions presented in this paper enable us to clarify the current state of the art and the emerging opportunities of PIML approaches, especially for building PHM systems that can work under the "small data and scarce physics knowledge" paradigm. [ABSTRACT FROM AUTHOR]