Interpretable crack features for the representation of kinematic fields in the case of fatigue overloads

Many engineering structures are subjected to variable amplitude loading. A number of studies investigate the effects of post overload, even-though it is crucial to describe what occurs during the overloading. The aim of this paper is to provide effective independent descriptors based on purely kinematic measurements for the analysis of overloading. Fatigue tests were conducted on a SENT specimen. Investigating crack propagation was through direct measurements using Digital Image Correlation and Linear Elastic Fracture Mechanics via Williams’ series expansion. The higher terms in Williams’ series expansion, referred to as crack features were analyzed in cycles with and without overload. In a case without overload, all features exhibit a proportional regime. Singular value decomposition (SVD) analysis confirms that a single feature is adequate to characterize the mechanism. In a cycle with overload, the regime changes during the overloading phase, making it a signature of this phase. In this case, the SVD analysis reveals that two descriptors are needed for these cycles. A subsequent analysis allows the definition of two physically interpretable features. This work presents a robust method to identify, based on kinematic measurements and SVD analysis, independent descriptors for the processes that occur during a cycle with overload.