Application of Barkhausen effect measurements for detection of near surface stress (abstract)

Abstract

Barkhausen effect emissions have been shown to be dependent on stress in previous work. This paper shows how the technique has been applied to evaluation of stress in automobile crankshafts. These components often fail prematurely due to residual tensile stress in the surface of the components, which leads to cracking and sudden fatigue failure. The measurements were made using an excitation frequency of 8 or 128 Hz with signal detection bandwidths of 3–15, 20–70, and 70–200 kHz. These corresponded to nominal magnetic field penetrations of 0.2, 0.07, and 0.02 mm. Results showed that measurements from the near surface (0.02 mm) were most sensitive to stress. A number of calibration experiments on different materials confirmed this result. In addition, it was found that low values of the root-mean-square Barkhausen voltage correlated with low tensile strength of the material. This measurement could, therefore, be used for detection of components that were likely to encounter early failure. A calibration of the Barkhausen voltage signal as a function of stress was obtained and this was in accordance with earlier theoretical calculations.