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Measurement of mechanical stresses in ferromagnetic materials on the analysis of magnetic anomalies

Antao Yu

 

It is known, that the permeability of ferromagnetic substances is also dependent on the mechanical stress. Based on this theory, there is a method called "stress-dependent magnetic flux leakage". This is a method, which is usually used to detect defects in iron and steel. But the question is, if there is a way to detect mechanical stress in a ferromagnetic material?

With the modern magnetic sensor, we are able to explore magnetic flux densities down to about 50 nT. That makes us also able to find the tiny difference magnetic flux density, due to mechanical stress.
In this project, we will use a GMR (Giant Magneto Resistance)-magnetometer as a magnetic sensor (see Figure 1). Some experiments are made to see if it is possible to determinate the area with different mechanical stress (see Figure 2).

Keywords: mfl, stress, magnetic flux leakage, ferromagnetic material, GMR

September 20, 2012

Figure 1: View of the system Figure 2: Results showing stress in a saw blade