Non-destructive residual stress for quality control
Barkhausen noise analysis method for residual stress measurement is based on a concept of inductive measurement of a noise-like signal, generated when a magnetic field is applied to a ferromagnetic sample. Ferromagnetic materials contain groups of magnetic dipoles, called domains, which act as individual magnets. AC magnetic fields will cause domain walls to move back and forth, which was first observed by Heinrich Barkhausen in 1919.
Two important material characteristics will affect the intensity of the Barkhausen noise signal. One is the presence and distribution of elastic stresses and the other is microstructure.
Compressive stresses will decrease the intensity of Barkhausen noise while tensile stresses increase it. This fact can be exploited so that measuring the intensity of Barkhausen noise can provide a signal for the amount of residual stress.
Barkhausen Noise Analysis is useful for
- Evaluation of residual stresses in steels
- Evaluation of microstructural changes
- Production quality control
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Photograph of a Barkhausen noise analysis measurement of a ground camshaft (Photo courtesy American Stress Technologies)