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The metal magnetic memory is used to detect the micro damage of structure based on the SMFL (self-magnetic flux leakage) effect, but it lacks an effective comprehensive diagnosis index suitable for the ferromagnetic material. In this paper, steel strand specimens were tensioned at different force levels, and the experimental study on the corrosion detection was carried out. Besides the monitoring analysis of the cable force, the initial structural magnetic field ΔBx0 and the surface SMFL signals Bx(α) induced by corrosion were both analysed. The results show that ΔBx0 curves of steel strand material present the periodic fluctuation. Considering ΔBx0 and measuring distance z, the proposed dimensionless damage analysis index X can be used for the quantitative research of corrosion diagnosis. The small influence of the cable force on index X is also illustrated. Moreover, the strong correlation that exists between the average maximum index X m a x ‾ and the corrosion ratio α is well fitted by the three-order polynomial curves. [ABSTRACT FROM AUTHOR]

The identification of cross-sectional loss in cables due to corrosion is crucial for evaluating the remaining strength of bridge cables. To accurately determine the cross-sectional loss rate, this paper derived a three-dimensional magnetic dipole model for spatial cable damage. The study employed an independently designed self-magnetic flux leakage (SMFL) sensor array to detect corrosion on a bundle of 37 parallel steel wires. The analysis investigated the correlation between corrosion degrees and SMFL signal features. The results show that the spatial magnetic field inversion collected by the sensor array device is more accurate. The cable damage location can be pinpointed by observing abrupt changes in the Bx and Bz curves. Additionally, this paper introduces five corrosion characterization features, all correlated with the cable cross-sectional loss rate. However, recognition stability using a single characteristic value is insufficient. The cable cross-sectional loss rate identification method, utilizing a back propagation neural network in conjunction with multiple characteristic indicators, demonstrates robust quantitative and adaptive capabilities. The maximum relative error of this method is 7.6%, offering a new perspective for future cable damage detection. [ABSTRACT FROM AUTHOR]

• The vibration effect concept of measuring displacement and defect deformation on the magnetic field is interpreted. • The increment of magnetic field change under vibration mainly depends on Δ B Def. • The quantitative characterization method of the magnetic field considering the vibration effect is proposed. • γ sum can effectively weaken the vibration effect on the magnetic characteristics of cable structure. The self-magnetic flux leakage (SMFL) method has excellent potential in corrosion measurement research of bridge stay cables and suspenders. However, the vibration effect in the cable's SMFL measurement is unclear and short of the systematic experimental analysis. Based on the magnetic field superposition principle, this study interpreted the vibration effect on steel cable structure magnetic field. The effect was innovatively summarized by the magnetic field increment resulting from the measuring displacement (Δ B Dis) and the defect deformation (Δ B Def). Then, the SMFL measurement experiment of the corroded steel strands during the vibration was carried out. The magnetic field distribution law and the influence of the corrosion loss ratio were also analyzed. The results show that Δ B Dis presents a "zero value" distribution law via the statistical histogram. The increment of the magnetic field under vibration mainly depends on Δ B Def , which positively correlates with the structure's corrosion degree and deformation curvature. An excellent linear correlation between the comprehensive characteristic parameter γ sum and the corrosion ratio is obtained. So, the quantitative characterization analysis method under vibration was proposed, and γ sum can weaken the vibration effect on the magnetic characteristics of cable structure. [ABSTRACT FROM AUTHOR]

• A theoretical analysis method of magneto-mechanical effect under initial corrosion was proposed. • The corrosion-stress coupling influence includes stress concentration and defect strain. • The magneto-mechanical effect coefficient under initial corrosion η x 0 is cubic nonlinearly correlated with stress σ. The influential mechanism between corrosion self-magnetic flux leakage and magneto-mechanical effect of ferromagnetic material is an urgent problem for the corrosion diagnosis of loaded cable structures. This study established the SMFL evolution basic model under different initial corrosion states, and the theoretical analysis method for the magneto-mechanical effect under various corrosion degrees was proposed. Then, the uniform corrosion experiment under increasing tensile loads was performed to verify its accuracy and availability. The results show that the tensile stress promotes the quadratic nonlinearly downward trend of the overall magnetization and the linearly downward trend of fluctuation distribution without corrosion. The magneto-mechanical effect under initial corrosion can be interpreted as the superposition of non-corrosion influence effect and corrosion-stress coupling effect. Moreover, the cubic nonlinear correlation of decreasing first and then increasing between η x 0 and σ is verified. This study provides a theoretical solution for the corrosion-stress coupling analysis of corroded and loaded cable structures. [ABSTRACT FROM AUTHOR]

• The evaluation index ' X ' was established to quantitatively analyze the SMFL signal of the corrosion. • A strong positive correlation was revealed between the index ' X ' and the corrosion loss ratio ' α '. • A probability evaluation method for the cable corrosion degree was proposed in association with the Bayesian model. • The evaluation criteria for the corrosion degree of cable structures were obtained. The corrosion and cross-sectional loss of steel wires inside cable structures seriously threaten the operational safety of bridges. In the present study, a probability evaluation method for the cable corrosion degree was proposed in association with the Bayesian model. Firstly, the evaluation index ' X ' was expressed based on the magnetic dipole model of self-magnetic flux leakage (SMFL), and corrosion detection experiments were carried out on both steel strands and wires. Then, the distributions of the measured SMFL signals were analyzed. The statistical law between ' X ' and the cross-sectional loss ratio ' α ' was depicted and revealed based on the experimental data. Finally, the positive correlation between ' X ' and ' α ' was quantified by four different levels, in turn, the evaluation criteria for the corrosion degree of cable structures were obtained. Via the comparative analysis with the different prior probability distribution of corrosion degree, the reliability of the evaluation criteria was verified. [ABSTRACT FROM AUTHOR]

This paper proposed a new computing method to quantitatively and non-destructively determine the corrosion of steel strands by analyzing the self-magnetic flux leakage (SMFL) signals from them. The magnetic dipole model and three growth models (Logistic model, Exponential model, and Linear model) were proposed to theoretically analyze the characteristic value of SMFL. Then, the experimental study on the corrosion detection by the magnetic sensor was carried out. The setup of the magnetic scanning device and signal collection method were also introduced. The results show that the Logistic Growth model is verified as the optimal model for calculating the magnetic field with good fitting effects. Combined with the experimental data analysis, the amplitudes of the calculated values (BxL(x,z) curves) agree with the measured values in general. This method provides significant application prospects for the evaluation of the corrosion and the residual bearing capacity of steel strand. [ABSTRACT FROM AUTHOR]

The self-magnetic flux leakage (SMFL) detection technique has great potential in the corrosion detection of bridge stay cables due to its advantages of small testing equipment, high accuracy, and fast testing rate. However, the vibration effect in the cable's SMFL detection is unclear. To address this, the influence of vibration on the magnetic field distribution of cable structure is analyzed theoretically. According to the theoretical model, the effect of vibration on SMFL detection primarily manifests as displacement changes (displacement-added magnetic field) and defect shape changes (deformation-added magnetic field). SMFL detection experiments are conducted on steel strands. The results demonstrate that the displacement-added magnetic field exhibits statistical characteristics in the form of a normal distribution, fluctuating around the zero value. The impact of the deformation-added magnetic field on SMFL is linearly correlated with the corrosion ratio c. Moreover, a corrosion characterization index A was proposed and has an excellent linear fit with the corrosion ratio c. The index A effectively improves the accuracy of corrosion detection and provides early warning for the maintenance of cable structures. [ABSTRACT FROM AUTHOR]

• The magnitude of SMFL signal of corroded steel strand is magnified by loading effect. • The corrosion degree dominates characteristic of SMFL signal despite loading effect. • A novel quantification index for corrosion degree of steel strands was proposed. • The correlation among characteristic index, load and corrosion ratio was explored. As for the corrosion damage quantification of steel strands by self-magnetic flux leakage (SMFL), the influence of load on cable-stayed bridges was seldomly studied. In this paper, an experimental study was conducted to analyze the loading impact of the damage quantification-based SMFL signal. A characteristic index C was proposed to evaluate the corrosion degree accurately. The experimental results show that the variation of the SMFL signal caused by the corrosion under the load condition is analogous to the unstressed strand under different measuring distances, corrosion widths, and corrosion degrees. The effect of corrosion damage still dominates the signal distribution of SMFL, but increasing load magnifies the SMFL signal's magnitude. The proposed characteristic index C can quantitatively characterize the corrosion damage of steel strands under different loading magnitudes and corrosion widths conditions. When the corrosion degree is less than 30.89%, the corrosion degree of tensile steel strands could be quantified by the proposed index C. [ABSTRACT FROM AUTHOR]

• An encapsulation method was proposed considering different environments. • REME sensors encapsulated with brass can resist the impact from sensors and rebars. • The monitoring accuracy was improved by more than 11.73% through encapsulation. Prestress, which is critical to prestressed concrete (PC) structures, can be monitored using resonance-enhanced magnetoelastic (REME) sensors. REME sensors inside the PC structure are influenced by adjacent sensors and adjacent rebars. However, the sensor's anti-electromagnetic interference (EMI) encapsulation is lacking. After clarifying the principle of the REME method, a finite element model was established. The influence of the encapsulation's electrical conductivity and magnetic permeability on the sensor's electromagnetic compatibility was analyzed. Prestress monitoring experiments were conducted. The results showed that the sensor encapsulated with brass can resist low-frequency EMI and high-frequency EMI. After encapsulating, the sensitivity of the induced voltage-prestress relationship to adjacent sensors was reduced by 52.07%, and that to adjacent rebars was increased by 14.54%. The corresponding prestress monitoring accuracy was increased by 20.86% and 24.49%, respectively. The higher monitoring accuracy verified the feasibility of the proposed encapsulation method, which can resist both low-frequency EMI and high-frequency EMI. [ABSTRACT FROM AUTHOR]

• The theoretical model of self-magnetic flux leakage for dual defects on bridge cables was derived. • The correlation between the self-magnetic flux leakage signals in three directions and the broken wire defects was explored. • A novel quantification method for the broken wire defects of the parallel steel wire bundle was proposed. • A three-dimensional line graph that can qualitatively determine the depth of broken radial wires was proposed. The wire breakage of bridge cable may result in potential bridge safety and durability problems. Therefore, it is urgent to develop an effective testing method for quantitatively evaluating wire breakage. In this paper, based on magnetic dipole theory, the dual defects magnetic dipole model of bridge cables was established to quantify the width of breakage. Then, the multi-dimensional self-magnetic flux leakage (SMFL) detection experiments were carried out for different wire breakage states of parallel steel wire bundles. The experimental results show that the distribution law of the theoretical model is consistent with the experimental results. Finally, a method was proposed to quantitatively characterize the axial wire breakage width of the cable using the Boltzmann fitting curve. In addition, a three-dimensional (3D) line graph was proposed to qualitatively evaluate the relative magnitude of the radial wire breakage depth. This study provides a theoretical basis for quantitatively evaluating bridge cables using the SMFL signals. [ABSTRACT FROM AUTHOR]

This paper presents a nondestructive test method to evaluate the residual bending strength of corroded reinforced concrete beam by analyzing the self-magnetic flux leakage (SMFL) signals. The automatic scanning device was equipped with a micromagnetic sensor and sensor-based experimental details were introduced. Next, the theoretical formula of the normal component HS(z) of the SMFL signal that originated from the corroded region was derived based on the magnetic dipole model and the experimental results were discussed. The results indicate that the experimental data of HS(z) are consistent with the theoretical calculations, both location and extent of the steel bars corrosion can be qualitatively determined by using HS(z). The gradient K of HS(z) is approximately linearly related to the loss rate, S, of the bending strength, which can be used to evaluate the residual bending strength of the corroded reinforced concrete beam. This work lays the foundation for evaluating the residual bending strength of corroded reinforced concrete beams using the SMFL signal; the micromagnetic sensor is further applied to the civil engineering. [ABSTRACT FROM AUTHOR]