This report is the summarised description of the series of experiments, which goal is to separate the contribution of stresses, residual plastic deformation and metal degradation to the Barkhausen noise (BN). The following are the most important results of this investigation: - The compression-tension experiments of thin plates followed by BN measurements with the help of Barkhausen transducer rotated around the axis, perpendicular to the plate's surface, showed that:
- the normalised BN spectral density (zero level corresponds to zero stresses) changes its sign when the angle of magnetic field direction relative to the deformation axis is close to 45 deg., what corresponds to the direction of maximum shear stresses;
- in this direction the BN is unsensitive to the variation of level of elastic deformation;
- there exists the angle diagrams of BN variations which are similar to Moore circles for biaxial stress state.
- The torsion experiments of tube-like specimens, followed by BN measurements in the direction of maximum shear stresses confirmed the insensitivity of BN to their variations.
- The measurements of BN angle diagrams made at thin plates subjected to elastic bending in opposite directions confirmed the existence of the directions of "insensitivity" of BN, but the corresponding angles strongly differed of 45 deg. The value of critical angle depends upon the deformation scheme and the form of calibration curve. In more complex cases the "critical point" on angle diagrams transforms to the "critical area".
- In the "critical directions" it becomes possible to provide the measurements of the level of metal degradation or the residual plastic deformation.
- The contribution of residual plastic deformation into BN signal is as well can be separated with the help of BN-elastic- plastic hysteresis loops. The last could be received with the help of the measurements of BN at thin plates subjected to elastic-plastic bending in opposite directions with growing deflection. The example of such loops made with the samples of middle carbon steel is presented.
The described experiments can be the fundamental of NDT technique based upon the special computerised procedure of calibration. It represents the measurement of angle diagrams of BN at the thin plates, subjected to elastic-plastic deformation with growing deflection. The developing of special software for computer control on this procedure is on the way now.
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