Nondestructive Determination of Stresses in Steel Components by Eddy Current Method

Abstract

Nondestructive eddy current (EC) method for evaluation of stresses in ferromagnetic steel components based on the stress-induced magnetic anisotropy (MA) changes was investigated. The proposed method is based on the rearrangement of the magnetic domains under stresses due to the reverse magnetostrictive effect (Villari effect). For evaluation of stresses special EC probe was developed. Investigations were carried out with the application of the conventional testing machine for tensile loading and the specially developed experimental setup for four-point loading for creation the adjusted tensile and compressive stresses on different sided of the loaded specimen. From results obtained some specific properties were determined: the magnetic-mechanical hysteresis existence and the invariance feature in relation to the structural state of the material. The last result can create the outlook for stress measurement independently of the structural state of material as opposed to other known magnetic methods based on coercivity or Barkhausen noise measurements. Two original practical applications of the MA technique for stress determination were realized: the evaluation of the welding-induced residual stresses and the estimation of stresses in the steel bridge framework during the launching to the pillars.

Evaluation of Welding Distortion and Hardness in the A36 Steel Plate Joints Using Different Cooling Media

“…The distortion and residual stresses in thin-plate butt joints in Metal Inert Gas (MIG) welding were also investigated, and the results showed the significant contribution of the plate speed and thickness to welding distortion and residual stress [11]. Furthermore, the microstructure and hardness due to thermal cycling in the Heat-Affected Zone (HAZ) were analyzed by applying the Rosenthal equation to welding thick and thin plates [12], while the stress on the steel bridge frame (ferromagnetic steel) was evaluated using the undamaged eddy current method [13]. An analysis was also conducted on the welding hot-dip galvanized steel with the resistance welding process using component variations during tensile-shear strength and ultimate strain tests [14].…”

Multi-Frequency Magnetic Induction Tomography System and Algorithm for Imaging Metallic Objects

“…Non-destructive testing and eddy-current testing (NDT and ECT, respectively) of metal components has been extensively investigated and successfully adopted as a tool in industry. However, in using ECT to render images for detecting corrosion [ 10 , 11 , 12 , 13 , 14 ], fatigue [ 15 , 16 ], defects [ 17 , 18 , 19 ] and physical loading [ 20 , 21 , 22 ], mechanical scanners are often employed [ 23 , 24 , 25 , 26 , 27 , 28 ]. Furthermore, while ECT is generally regarded as non-contact, close proximity sensor positioning is usually required.…”

“…Ferrous metals exhibit a change in magnetic susceptibility when mechanically loaded (inverse magnetostrictive or Villari effect). While under physical deformation, the alignment of magnetic domains within the material grain structure tends to align with the axis of the applied force [ 20 ]. Ferrous metals with helical domains, caused by torsional stress, also show a change in magnetic susceptibility; the Matteucci effect [ 21 ].…”

“…Variations in stress are therefore reflected as changes in the inductance of coils magnetically coupled to the sample, or the coupling factor of transformer style sensors, as found in MIT systems [ 36 , 37 , 38 ]. Residual stress in ferrous materials, resulting from quenching and phase transformations, are also indirectly detectable using eddy-current methods [ 15 , 16 , 20 , 22 ]. Li et al describe a method for evaluating the yield stress in cold rolled steel, where the sample is magnetically biased with a low-frequency magnetic field, driving the sample through its hysteresis loop, while recording the complex impedance of a 5 kHz ECT sensor coil [ 25 ].…”