Research Paper: Experimental Study of the Effect of Stress on the Magnetic Signatures of a Steel Sample

Before sailing, submarines with ferromagnetic hulls are demagnetized to avoid damage and detection by sea mines and airborne systems. The increase in the residual magnetization of the submarine body after demagnetization due to the rising and falling can reduce the effect of demagnetization. This study aimed to investigate how internal hydrostatic pressure affects the magnetic signatures of a demagnetized submarine model. Magnetic sensors were placed at specific points under the body, and the changes in magnetic signatures were recorded when pressure was applied from 0 to 60 bar. The results show that by increasing the pressure up to 60 bar before demagnetization, the magnetic field components originating from the sample's internal stresses showed a linear increase. After depressurization, there was an exponential decrease followed by a subsequent increase in permanent magnetization of about 6%. However, after demagnetization, as the pressure increased up to 60 bar, the magnetic field generated by internal stresses in the sample increased by about 27%, but upon decreasing pressure, this magnetic field did not decrease but remained unchanged. This phenomenon negatively impacted the performance of the deperming process. Also, for further investigation, the increasing trend of magnetic signatures was evaluated at pressures of 30, 45, and 60 bar.