What happens to the sides of a small crack when a magnetic field is applied to the metal when you use MT?
When a magnetic field is applied to a metal during Magnetic Testing (MT), it can affect the sides of a small crack in the following ways:
1. Attraction force: If the metal is ferromagnetic, the magnetic field can create a localized attraction force on the sides of the crack. The magnetic field lines tend to concentrate around the crack, causing the crack faces to be pulled towards each other.
2. Magnetic flux leakage: In the presence of a crack, the magnetic field lines tend to "leak" out from the metal surface and exhibit a distortion in their path. This leakage of magnetic flux can be detected and visualized using suitable techniques, indicating the presence and dimensions of the crack.
3. Magnetic particle deposition: In some cases, a fine magnetic powder or liquid containing magnetic particles may be applied to the metal surface prior to the application of the magnetic field. These particles can align themselves along the magnetic field lines and tend to accumulate at the edges of the crack. This deposition of magnetic particles helps enhance the visibility and detection of the crack.
Overall, the effect of a magnetic field on the sides of a small crack during MT involves a combination of attractive forces, magnetic flux leakage, and magnetic particle deposition, all of which aid in the detection and evaluation of the crack.