Characterization of microstructure and residual stresses using Barkhausen noise measurements

Micromagnetic measurement methods based on Barkhausen Noise (BN) measurements are increasingly being used as a versatile and cost effective tool for in-situ examination and evaluation of microstructural changes. They are also used for measurement of surface residual stresses. Interpretation of the observations and measurements, however, require validation with the help of appropriate calibration procedures.

In the present paper, we examine the characterization of a broad spectrum of microstructures such as produced in steels and also lattice strains which sometimes accompany the microstructural changes. Such changes also affect the BN response. Characteristic residual lattice strains or residual stress patterns also get generated around stress raisers including flaws such as surface cracks which need to be detected and evaluated for their consequences during continued service exposure of the material. We will present observations of the mapping of surface residual stress pattern in the vicinity of a part through surface crack produced by controlled fatigue loading of a 15 mm thick martensitic stainless steel plate showing residual stress variations around a dormant crack.