Detection of surface cracks in ferromagnetic materials by C-scan mapping of residual stresses using Barkhausen emissions

Surface cracks can develop in components due to residual stresses, fatigue, stress corrosion cracking, corrosion fatigue, etc, during service exposure. Different non-destructive testing (NDT) methods are employed to detect and monitor such cracks. Magnetic Barkhausen Noise (MBN) analysis is one such technique that is used for in situ examination of microstructural anomalies or stress patterns. In the present work, we study the applicability of MBN for the detection of surface cracks. A part through surface crack was created by controlled fatigue loading of a martensitic stainless steel plate. The surface of the sample was scanned for BN emissions in incremental steps parallel and perpendicular to the crack. Measurements of MBN signal strength were recorded and assessed. Localized peaks in the MBN values observed whilst scanning sample surface can reveal the presence of flaws. Furthermore, the remnant stress pattern ahead of the crack tip as well as in the wake of the crack can get reflected in the measured MBN values. The observations carried out show that the surface scan carried out with MBN measurements can be a good non-destructive method for in situ NDT to detect and characterize surface cracks.