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In the real world, the main cables of suspension bridges are commonly inspected by conducting a periodic visual inspection of the exterior cover of the cable. Although there is a need to conduct a nondestructive evaluation (NDE) of the damage of the main cable, a suitable NDE technique has not yet been developed due to the large diameter and low accessibility of the cable. This study investigates a magnetic sensing cross-sectional loss quantification method that can detect internal and external damage to the main cables. This main cable NDE method applies an extremely low-frequency alternating current (ELF-AC) magnetization method and search coil sensor-based total flux measurement. A total flux sensor head consists of a magnetization yoke and a search coil sensor. To magnetize the main cable, a magnetic field was generated by applying a triangular ELF-AC voltage to the electromagnet yoke. The sensing part measures the magnetic flux that passes through the search coil, and the B-H loop was then obtained using the relationship between the ELF-AC voltage that has been input and the total flux that was measured. Also, the cross-sectional loss can be quantified using a variation of magnetic features from the B-H loop. To verify the feasibility of using the proposed NDE technique, a series of experiments were performed using a main cable specimen with a gradual increase in the cross-sectional loss. Finally, the relationship between the cross-sectional loss and extracted magnetic feature was determined and used to quantify the cross-sectional loss via the proposed method. [ABSTRACT FROM AUTHOR]

A magnetic flux leakage method was applied to detect damage when inspecting steel wire rope. A multi-channel magnetic flux leakage sensor head was fabricated using Hall sensors and permanent magnets to adapt to the wire rope. Three types of artificial damage were created on a wire rope specimen. The magnetic flux leakage sensor head scanned the damaged specimen to measure the magnetic flux density while the damage was expanding in three steps. Signal processing processes including the enveloping process based on Hilbert transform were performed to clarify the flux leakage signal due to the damage. The enveloped signals were then analyzed for objective damage detection by comparing with the threshold value. For improvement of quantitative analysis, three types of new damage indexes that utilize the relationship between the enveloped magnetic flux leakage signal and the threshold value were additionally proposed. By using the proposed damage indexes and the general damage indexes for the magnetic flux leakage method, the detected magnetic flux leakage signals from each damage type were quantified. The trends of the extracted damage indexes according to damage levels were analyzed to examine the applicability and reliability of the proposed damage indexes for the magnetic flux leakage based wire rope inspection. [ABSTRACT FROM AUTHOR]

In this study, the hardening process of ultra high performance concrete (UHPC) was monitored non-destructively using a single embedded sensor system and the characteristics of guided waves, especially the Lamb wave. Lamb wave propagation depends on the material properties of the medium and boundary conditions. Since the boundary conditions of the embedded sensor system continuously change during the hardening process of concrete materials, the measured characteristics of the propagating waves also vary. To understand the variations in wave propagation, the Lamb modes were decomposed using the polarization characteristics of piezoelectric sensors, which were used to measure wave responses. Additionally, a traditional penetration resistance method was adopted to estimate the time for phase transition of UHPC. The decomposed Lamb modes were compared to measurements of penetration resistance. The strength development of UHPC, with and without short-fiber reinforcement, was estimated using the variation of patterns of the decomposed Lamb modes after the phase transition. Based on the proposed methodology, which measures the propagation and variation of the Lamb waves, it is possible to estimate the time of phase transition and the strength development of UHPC. [ABSTRACT FROM AUTHOR]

In this study, a magnetic flux leakage (MFL) method, known to be a suitable non-destructive evaluation (NDE) method for continuum ferromagnetic structures, was used to detect local damage when inspecting steel wire ropes. To demonstrate the proposed damage detection method through experiments, a multi-channel MFL sensor head was fabricated using a Hall sensor array and magnetic yokes to adapt to the wire rope. To prepare the damaged wire-rope specimens, several different amounts of artificial damages were inflicted on wire ropes. The MFL sensor head was used to scan the damaged specimens to measure the magnetic flux signals. After obtaining the signals, a series of signal processing steps, including the enveloping process based on the Hilbert transform (HT), was performed to better recognize the MFL signals by reducing the unexpected noise. The enveloped signals were then analyzed for objective damage detection by comparing them with a threshold that was established based on the generalized extreme value (GEV) distribution. The detected MFL signals that exceed the threshold were analyzed quantitatively by extracting the magnetic features from the MFL signals. To improve the quantitative analysis, damage indexes based on the relationship between the enveloped MFL signal and the threshold value were also utilized, along with a general damage index for the MFL method. The detected MFL signals for each damage type were quantified by using the proposed damage indexes and the general damage indexes for the MFL method. Finally, an artificial neural network (ANN) based multi-stage pattern recognition method using extracted multi-scale damage indexes was implemented to automatically estimate the severity of the damage. To analyze the reliability of the MFL-based automated wire rope NDE method, the accuracy and reliability were evaluated by comparing the repeatedly estimated damage size and the actual damage size. [ABSTRACT FROM AUTHOR]

In this study, a noncontact non-destructive testing method is implemented to visualize damages of a pipeline structure. An ND:YAG pulsed laser system was used to generate guided waves and a galvanometer-based laser scanner scans a specific area to find damage location. The wave responses were measured using a piezoelectric sensor attached to the pipeline. The measured time and spatial responses were transformed to data in frequency and wavenumber domains through three-dimensional Fourier transform. Damage-sensitive features could be obtained using wavenumber filter to extract standing wave energy. A flaw imaging technique of the pipeline structure was conducted by calculating root mean square. Notches and thickness reduction at a pipeline structure were investigated to verify the effectiveness and the robustness of the proposed non-destructive testing approach. Additionally, a series of experiments were repeated under heating condition to consider the real-world pipeline structures. [ABSTRACT FROM AUTHOR]

In this research, a noncontact nondestructive testing (NDT) method is proposed to detect the fatigue crack and to identify the location of the damage. To achieve this goal, Lamb wave propagation of a plate-like structure, which is induced by scanning laser source actuation system, is analyzed. A ND:YAG pulsed laser system is used to generate Lamb wave exerted at the multiple points of a steel coupon, and a piezoelectric sensor is installed to measure the structural responses. Multiple time signals measured by the piezoelectric sensor are aligned along the vertical and horizontal axes corresponding to laser impinging points so that 3-dimensional data can be constructed. Then, the 3-dimensional data is sliced along the time axis to visualize the wave propagation. The scattering of Lamb wave due to the damage can be described in the wave propagation image, and hence the damage can be localized and quantified. Damage-sensitive features, which are reflected wave from the damage, are clearly extracted by wave-number filtering based on the 3-dimensional Fourier transform of the visualized data. Structural members with fatigue cracks are investigated to verify the effectiveness and the robustness of the proposed NDT approach. [ABSTRACT FROM PUBLISHER]

This article presents an experimental study using an active sensing device that consists of a miniaturized impedance-measuring chip (AD5933) and a self-sensing macrofiber composite (MFC) patch to detect corrosion in aluminum structures widely used for aerospace, civil, and mechanical systems. A simple beam structure made from a 6063 T5 aluminum alloy was selected for corrosion-detection testing. Four different corrosion cases with two different locations and two different degrees at each location were artificially inflicted on the beam using hydrochloric (HCI) acid. To identify the degrees and locations of the corrosion, the electromechanical impedance-based damage-detection technique using the proposed active sensing device was investigated. Root-mean-square deviation (RMSD) metric of the real part of the impedances obtained from the MFC patch was selected as a damage-sensitive feature. Experimental results have verified that the proposed approach can be an effective tool for detection and quantification of corrosion in aluminum structures. [ABSTRACT FROM AUTHOR]

Recently, the early-age strength prediction for RC (reinforced concrete) structures has been an important topic in the construction industry, relating to project-time reduction and structural safety. To address this, numerous destructive and NDTs (non-destructive tests) are applied to monitor the early-age strength development of concrete. This study elaborates on the NDT techniques of ultrasonic wave propagation and concrete maturity for the estimation of compressive strength development. The results of these comparative estimation approaches comprise the concrete maturity method, penetration resistance test, and an ultrasonic wave analysis. There is variation of the phase transition in the concrete paste with the changing of boundary limitations of the material in accordance with curing time, so with the formation of phase-transition changes, changes in the velocities of ultrasonic waves occur. As the process of hydration takes place, the maturity method produces a maturity index using the time-feature reflection on the strength-development process of the concrete. Embedded smart temperature sensors (SmartRock) and PZT (piezoelectric) sensors were used for the data acquisition of hydration temperature history and wave propagation. This study suggests a novel relationship between wave propagation, penetration tests, and hydration temperature, and creates a method that relies on the responses of resonant frequency changes with the change of boundary conditions caused by the strength-gain of the concrete specimen. Calculating the changes of these features provides a pattern for estimating concrete strength. The results for the specimens were validated by comparing the strength results with the penetration resistance test by a universal testing machine (UTM). An algorithm used to relate the concrete maturity and ultrasonic wave propagation to the concrete compressive strength. This study leads to a method of acquiring data for forecasting in-situ early-age strength of concrete, used for secure construction of concrete structures, that is fast, cost effective, and comprehensive for SHM (structural health monitoring). [ABSTRACT FROM AUTHOR]