Grain-level visualization of stress-strain distribution on fatigue crack via self-magnetic flux density: a brief experimental investigation

Fatigue cracks exhibit unpredictable and rapid propagation, presenting challenges in comprehending their initiation, influenced by various physical and chemical parameters. To gain deeper insights into the nucleation and growth, understanding the convergence phenomenon in ferromagnetic materials requires visualization of the local stresses and phase changes around the defect. This necessitates a measurement system capable of not only imaging the defect but also stress mapping at high spatial resolution, ideally at grain-level. In this study, we explore how this can be achieved by integrating three-axis tunnel magnetoresistive (TMR) sensor with optical microscopy images. This integration was expected to facilitate the visualization of self-magnetic flux density and enable microstructure analysis on the material's surface. Employing this mapping technique, we observe and discuss the stress distribution around the crack at the grain level with three variation of defect depths direction: 0, 30, and 60 degrees.