Role of external magnetic field during friction of ferromagnetic materials

Effect of magnetic field on the friction between two crossed steel cylinders in reciprocating motion in ambient air was experimentally studied in a speed range of 0.012–0.24 m/s and a load range of 0.5–6 N. Upon the applying of an external magnetic field, the friction force and the acoustic emission (AE) signal increased while the wear rate decreased. The increase of friction force is mainly ascribed to the magnetic field induced attractive force between cylinders acting as an extra normal load, which can be substituted by a mechanically exerted equivalent normal load to obtain the similar lateral force and AE signal. While the friction coefficient decreased with the increase of the normal load, the friction coefficient upon applying magnetic field decreased due to a higher equivalent normal load. The relationships among friction coefficient, sliding velocity, normal load and AE signal have been extensively discussed. Analysis of the energy transition from friction to AE signal showed that the external magnetic field could suppress the elastic wave releasing during friction. Also the wear was alleviated by the lubrication of debris concentrated around the contact region in the presence of a magnetic field.

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► Friction coefficient will decrease due to the high equivalent normal load.
► Net normal load induced by magnetic field equals to the force exerted mechanically.
► Acoustic emission releasing rate is slightly restrained under the magnetic field.
► The wear is levitated due to the concentration of the debris around contact point.