A study on influence of plastic deformation on the global conductivity and permeability of carbon steel

Abstract

Non-destructive evaluation (NDE) techniques are indispensable for inspection of damage in structures of carbon steel, which is widely used in many industries. In this paper, experimental and numerical studies were conducted to investigate the electromagnetic property variations of carbon steel Q195 due to plastic strain by using the 4-probe potential drop method and ECT aiming at NDE applications. A series of specimens were fabricated and uniform global plastic strains of different levels were introduced to the specimens by tensile testing. 4-probe potential drop measurements were carried out to obtain the conductivity information at first. It is found that the macro conductivity is not affected significantly by the plastic strain once taking into account the influence of the cross-sectional area reduction of the specimens. Combining the results of numerical analysis using a code of A_r formulation with the measured ECT signals, the permeability of specimens with various plastic damages was evaluated through inverse analysis. It is proved that the ECT signal change due to plastic damages is mainly caused by the variation of permeability, which gives a good possibility to evaluate the plastic damage with a magnetic NDE method.

Evaluation of the Residual Plastic Deformation in Low-Carbon Steel with the Oscillatory Rotating Eddy Current Method

“…As stated in the Ref. [18], the permeability decreases due to the increment of plastic deformation occurred in the carbon steel. For a given excitation frequency, the reduction in permeability of the steel leads to an increase in the penetration depth of the eddy current field.…”

“…5i). The imaginary part of the impedance mainly reflected the information of magnetic permeability, which strongly relied on both the plastic strain and magnetization frequency [18]. The anisotropy of magnetic permeability is mainly determined by the orientation of hard or easy magnetization axis of the material.…”

Characterization of Elastic and Plastic Behaviors in Steel Plate Based on Eddy Current Technique Using a Portable Impedance Analyzer

“…Both the permeability and the ECS impedance amplitude were found to monotonously increase with the increase in the elastic stress. On the contrary, Cai et al [20] reported that the increasing residual plastic strain decreased the permeability of carbon steels. The observed monotonous dependency of eddy current signal features on individual elastic stress or plastic strain may allow nondestructive evaluations.…”

Mechanism study of the residual stress evaluation of low-carbon steels using the eddy current magnetic signature method

“…Magnetic non-destructive testing methods, such as the magnetic Barkhausen noise method [1], harmonic analysis [2], the use of a magnetic point probe [3], eddy current testing (ECT) [4], and the magnetic incremental permeability (MIP) method [5,6,7], have received attention as means to evaluating the mechanical residual stress and strain of ferromagnetic steels.…”