Improvement of the Barkhausen noise method for stress evaluation

Abstract Envelopes of Barkhausen noise bursts are measured for ferritic-pearlitic, tempered microalloyed, 3.5Ni and 9Ni steels in an unloaded state and under tensile stresses, and the area Ar, peak amplitude Vm and restricted area RAr of these envelopes are determined. RAr is evaluated from the portion of the signature which has simultaneously a high and unique dependence on stress. In the case of ferritic-pearlitic steels, tensile stress increases Barkhausen activity at the leading edge of the envelope which thus constitutes a convenient time range for determining RAr. Ar and Vm values suffer from a non-unique stress dependence in the tempered steel, i.e. the existence of a local maximum, but the stress response of RAr remains unique, with spatial scatter, at least up to 300 MPa. A directional contribution of the texture to noise values impairs the possibility for evaluating stress magnitudes in the 3.5Ni steel, while the 9Ni steel has a high stress response and pronounced spatial variation in noise. The RAr figures represent an improvement over Vm and Ar values as stress measurements, especially for tempered steels and to a lesser extent ferritic-pearlitic steels, whereas all the parameters mentioned have similar stress responses for Ni steels.