Evaluation of fatigue crack network growth in cast iron for different biaxial loading paths via full-field measurements

• New DIC technique utilized to monitor crack network formation in fatigue.
• Original biaxial experiments on nodular graphite cast iron.
• Analysis of loading path on fatigue properties.

This paper proposes a new method for monitoring fatigue crack network initiation and growth based on Digital Image Correlation (DIC), and reports on in-plane biaxial fatigue experiments with two different loading paths and two amplitudes on nodular graphite cast iron. The central thinned part of cross-shaped samples is observed on two scales. Regularized Digital Image Correlation (DIC) is used to measure displacement fields and to reveal DIC residuals, i.e., image differences that cannot be accounted for with registration. The detailed strain histories are compared at different scales and for the different loading regimes. DIC and mechanical residuals, i.e., local deviations of the displacement field from being the solution to an elastic problem, enable for the crack network detection and quantification with respect to the number of cycles. The relative damage severity and fatigue lifetime of different loading paths experiencing identical load magnitudes are analyzed for the tested material.