Effective Second Moment of Load Path (ESMLP) Method for Multiaxial Fatigue Damage and Life Assessment 2023-01-0724

Time-domain and frequency domain methods are two common methods for fatigue damage and life assessment. The frequency domain fatigue assessment methods are becoming increasingly popular recently because of their unique advantages over the traditional time-domain methods. Recently, a series of moment of load path based multiaxial fatigue life assessment approaches have been developed. Among them, the most recently developed effective second moment of load path (ESMLP) approach demonstrates its potentials of conducting fatigue damage and life assessment accurately and efficiently. ESMLP can be used for fatigue analysis even without resorting to cycle counting because of its unique mathematical and physical properties, such as quadratic form in the kernel of the moment integral, rotationally invariant, and being proportional to damage. Developing a better parameter for frequency-domain analysis is the driving force behind the development of ESMLP as a new fatigue damage parameter. The time domain properties and applications of ESMLP have been demonstrated recently, and it is found that ESMLP works well in correlating time-domain data including asynchronous test data.

In this paper, the basic mathematical structures and key features of ESMLP in frequency domain are presented. Procedures of implementing ESMLP into frequency-domain analysis are provided. Examples of well-studied loading paths, such as ASTM 1049 uniaxial loading examples and multiaxial (synchronous and asynchronous) loading cases, are analyzed and presented to demonstrate ESMLP based frequency-domain assessment procedure. The potentials of ESMLP in frequency-domain analysis of variable amplitude multiaxial fatigue data and knowledge-informed machine learning are also discussed.