An experimental investigation was conducted to address the durability aspect of steel-reinforced concrete (RC) culverts using an accelerated aging environment. Analysis of the experimental data was built on the acoustic emission (AE) activity. AE methodologies were used to compare the behaviors of RC culverts after an aging process using a rate-process analysis. In the rate-process analysis, probability density functions (PDF) of AE activity were obtained from the experimental data to indicate the damage status of experimental specimens. This AE assessment procedure included only the incidence of an AE event, ignoring any features of the AE signal itself. Results showed reliable and quantitative assessment based on AE activity for defining the relative strengths of steel-reinforced specimens.
This paper introduces a laser scanning technique to characterize internal planar defects in a specimen with parallel boundaries. Based on the principles of laser-based ultrasonic shear waves and shadowing, a procedure to determine flaw location, size, and orientation is described. The key feature of this scheme is the use of an optimum wave propagation angle where the maximum shear wave propagates. The feasibility of the approach is evidenced by testing specimens with various controlled and natural internal flaws. The experimental results are promising, in that the flaw characteristics can be determined with good accuracy. It is found that the scheme is especially useful for characterizing transverse-type flaws. The limitations of the technique are also addressed.
The scattering of probe-generated ultrasonic fields incident upon a strip-like crack in an anisotropic half-space is discussed. In the situation considered, two possibly coinciding probes are attached to the surface of the half-space. One is transmitting waves incident upon the crack and the other one is receiving the scattered waves. An electric signal response is calculated via an electromechanical reciprocity relation. For a crack far away from the probes and the surface, an approximate expression is calculated. Several numerical examples are presented for an isotropic and a transversely isotropic solid. The results are presented as A-, B-, and C-scans.
In this article, the theoretical and experimental aspects of three active thermography approaches: pulsed thermography (PT), lock-in thermography (LT), and vibrothermography (VT), are discussed in relation to the nondestructive evaluation (NDE) of honeycomb sandwich structures. For this purpose, two standard specimens with simulated defects (delaminations, core unbonds, excessive adhesive, and crushed core) were tested, and results were processed, examined, and compared. As will be pointed out, the similarities and differences between these active approaches allow conclusions to be made about the most suitable approach for a particular application. In addition, results from NDE inspection by X-rays and c-scan ultrasounds are provided and discussed for reference.
In this, a method to measure welding residual stress in butt-welded joints of carbon steel plates using longitudinal critically refracted wave (L cr wave) is proposed. Cross-correlation was employed to calculate the difference in time of flight between L cr wave, and the optimal step length for the measurements is discussed. To determine L cr wave acoustoelastic coefficient of the heat affected zone (HAZ), the relationship between the L cr wave acoustoelastic coefficient and the grain size is established. The results show that one cycle is the optimal step length for the difference in the time-of-flight calculation, and with increasing grain size increase, L cr wave acoustoelastic coefficient decreases in the form of a power function. In addition, grain size can be determined by using amplitude of the L cr wave, so that the measured value of welding residual stress in HAZ can be corrected. The welding residual stress in melted zone (MZ) is corrected by calibrating acoustoelastic coefficient of the MZ. The acoustoelastic coefficient of the MZ is larger than that of parent material (PM). At last, welding residual stress in the butt-weld joint is measured and corrected with the L cr wave technique. The results are verified by the hole drilling method.
Nondestructive evaluation (NDE) techniques of phased array ultrasonic testing (PAUT) and digital X-ray radiography were employed on friction stir (FS)-welded Aluminum Alloy (AA)-2219-T87 specimens. PAUT intricacies required for scanning of FS-welded specimens with a 10-MHz 32-element transducer are discussed. The time corrected gain (TCG) calibration is required for scanning with an increase in index offset to compensate for decrease in A-Scan signal peak amplitude. Calibration techniques to find small defects with appropriate size tolerances are also established. The NDE technique of digital X-ray radiography is compared to PAUT, where it was found that a calibrated PAUT system is able to discover defects less than 0.2 mm where X-ray radiography could not. Incomplete penetration (IP), wormhole (WH), surface cavity (SC), and internal void (IV) defects are analyzed. Furthermore, an online PAUT system for FSW has been developed and successfully tested. The work provided herein will provide a gateway for an ultimate goal of an automated PAUT online sensing system.
Magnetic memory method (MMM) is widely used for diagnosing ferromagnetic material on early stage as a nondestructive technology, but no clear description exists for the influence of stress on MMM signals at the micro-defect position on the surface of steel wire yet. Hence, based on traditional magnetic charge model, a stress-dependent magnetic charge model that combined the Jiles magneto-mechanical constitutive relation was intended to calculate the MMM signals around micro-defect on surface of steel wire. Meanwhile, the H p (y) signals on surface of steel wire with different defects were measured during the whole tension test. By comparing the results of theoretical model and experiment, some conclusions can be drawn. First, the position of vale-peak on H p (y) signals curves can be used to determine the micro-defect on steel wire. Secondly, the vale-peak amplitude (S v-p ) and vale-peak width (L v-p ) of H p (y) signals curves, as two characteristic parameters of magnetic signals, not only can reflect the variations of defect depth and defect width, but also judge the load subjected by specimen. S v-p has an approximate growth with the increase of defect depth as a whole, but decreases with the increase of loads. And the effect of load on S v-p increases with defect depth. L v-p has an approximate growth with the increase of defect width as a whole, but does not change with the increase of loads. Finally, the stress-dependent magnetic charge model can be better to reflect the changing laws of H p (y) signals around defect and can be used for the numerical analysis of MMM signals on surface of steel wire.
The magnetic flux leakage (MFL) inspection technology is widely used in pipeline industry to detect defects to ensure pipeline safety. During the high-speed inspection, a relative motion occurred between the pipeline inspection gauge (PIG) and the steel pipe wall will generate motion-induced eddy current (MIEC). There is a lack of research on analyzing the effect of MIEC on high-speed MFL inspection for thick-wall steel pipe. In this article, a three-dimensional (3D) finite-element method (FEM) simulations are conducted with an inspection speed range of 0 m/s to 8 m/s and a wall thickness range of 8 mm to 15 mm. Simulation results show that both high-speed inspection and thick-wall thickness will decrease the magnetization of steel pipe. It is observed that, at the speed of 8 m/s and the thickness of 15 mm, the magnetic field strength is lower than 2 kA/m and the steel pipe exits from the magnetic saturation zone, which causes the severe distortion of three-axis MFL signals, and the signal-to-noise ratio (SNR) is lower than 6 dB. A high-speed PIG is developed here for experiments to measure the three-axis MFL signals. The characteristics of simulated and measured MFL signals are found to be quite consistent.
This paper presents a probabilistic approach to continuously track the sequential movement of the multiple impacts considered as acoustic emission (AE) sources. Continuous wavelet transform (CWT) analysis is used to determine the time of arrival (TOA) of the different AE hits by taking into account systematic errors due to the Heisenberg uncertainty. Then, the Extended Kalman Filter (EKF) is applied to simultaneously estimate the locations of impact points and the group velocity of the involved Lamb waves at a specific frequency. To validate the performance of the proposed probabilistic approach, including uncertainties from modeling error and measurement noise, experiments on a copper panel are performed using AE hits generated by Pencil-Lead Breaks (PLBs). Measurements help appreciate robustness of the proposed approach with consequent potential applications in structural health monitoring of industrial parts and structures.
This study systematically determined the transmission and receiving sensitivities of over twenty transducers. Four types of sensitivities were evaluated for both transmission and receiving sensitivities. These are found to be different from each other and the reversibility or reciprocity conditions exist only in exceptional cases. Using their observed behavior as the basis, we critically examined the calibration methods developed to characterize them, including those based on laser interferometry and the acoustic reciprocity principle. Serious flaws in some of the reciprocity methods are uncovered, which can be rectified by using the HillAdams method. Four procedures emerged as workable calibration methods for contact ultrasonic and acoustic emission transducers. However, current experimental uncertainties limit the upper frequency to 2 MHz.
Novel fuels are part of the nationwide effort to reduce the enrichment of Uranium for energy production. Fuel performance is determined by irradiating tfuel plates. The plate checker used in this experiment at Idaho National Lab (INL) performs nondestructive testing on fuel rod and plate geometries with two different types of sensors: eddy current and digital thickness gauges. The sensors measure oxide growth and sample thickness on research fuels, respectively. Sensor measurement accuracy is crucial because even microns of error is significant when determining the viability of an experimental fuel. One parameter known to affect the eddy current and digital gauge sensors is temperature. Since both sensor accuracies depend on the ambient temperature of the system, the plate checker has been characterized for these sensitivities. Additionally, the manufacturer of the digital gauge probes has noted a rather large coefficient of thermal expansion for their linear scale. In this work, the effect of temperature on the eddy current and digital gauge probes is evaluated, and thickness measurements are provided as empirical functions of temperature. Additionally, an experimental coefficient of thermal expansion for the probe material has been reported and compared with the manufacturer's specifications.
In this work, a novel migration method is applied to Ground-Penetrating Radar (GPR) data to detect the internal flaws of ornamental stone blocks. To detect and classify fractures in accordance with their spatial orientation, a Shift-Invariant Probabilistic Latent Component Analysis (SI-PLCA) is proposed. GPR simulations are conducted using modeling software to test several types of fractures (with different positions, thicknesses, and lengths) in rock blocks and to train several patterns as inputs for the SI-PLCA method. An 800 MHz antenna is used to assess both simulated and real data. The accuracy rate of the proposed approach is evaluated and compared with that of classical migration methods for detection and is compared to a Template Matching approach for classification; promising results are obtained. In addition, GPR is applied to two blocks of a rock type known commercially as Crema Marfil. The 3D fracture maps obtained from the proposed approach are compared with the stone slabs from the cutting process. The results show that the proposed approach applied to GPR radargrams is an effective method for determining the internal structure of stone materials, particularly for detecting and classifying fractures.
The effect of uniaxial compression on the development of damage in reinforced concrete has been studied, using the parameters of the electric response to elastic impact. During the quasistatic loading of the samples at a constant speed, a weak impact is produced on the lateral surface of the sample during a specified period of time, and an electrical response to this impact is measured. Consistent patterns in the changes of the parameters of the electric response with various loads have been identified. Computer simulation of the parameters of elastic waves in reinforced concrete subjected to mechanical impact has also been used. Based on the simulation, the parameters of the electric response have been calculated using the mechanoelectrical transduction model. Good consistency of theoretical and experimental signals confirms the relationship between the electric response and the interaction of elastic waves and fractures in reinforced concrete caused by uniaxial compression. Based on the electric response data corroborated with the computational results, diagnostic criteria have been obtained which make it possible to predict failure of reinforced concrete structure long before it occurs.
For enhanced detection of flaws in engineering components using magnetic flux leakage (MFL) technique, measurement of the leakage magnetic field components along the three perpendicular directions is beneficial. This article presents the three dimensional-magnetic flux leakage (3D-MFL) modeling and experimental studies carried out on carbon steel plates. Magnetic dipole model has been used for the prediction of MFL signals and images. Sensitivity of the MFL signals peak amplitudes of tangential (H X ), circumferential (H Y ), and normal (H Z ) components with respect to flaw length, width, depth and lift-off have been studied. A 3D-GMR sensor has been used for simultaneous measurement of all the three components of leakage magnetic fields from surface flaws in 12 mm thick carbon steel plates. The experimental MFL images have been compared with the model predicted MFL images. The sensor has shown the capability to detect and image 0.9 mm deep surface flaws with a signal to noise ratio of 8 dB. Principal component analysis (PCA)-based image fusion has been performed for fusion of the 3D-MFL images to obtain a geometrical profile of the flaws. Study reveals that 3D-GMR enhances the capability for detection of flaws having irregular geometries.
The aim in this article is to evaluate microstructural changes, hardness variations, and wear behavior of H13 hot work tool steel as a function of austenitizing and tempering temperature using nondestructive magnetic hysteresis loop method. To obtain different microstructural characteristics in the H13 specimens, austenitizing and tempering temperatures were varied in the range of 1,050-1,100°C and 200-650°C, respectively. The microstructural features, hardness, and wear loss were characterized using X-ray diffraction/metallographic examinations, hardness measurements, and a pin-on-disk wear tester, respectively. The relations between features obtained from the conventional methods and parameters extracted from the magnetic hysteresis loops were established. Results demonstrate that the proposed nondestructive method is able to assess the wear behavior of the heat treated H13 tool steels. Besides, a standard Generalized Regression Neural Network (GRNN) was trained with a training dataset and then used to estimate the hardness of a given sample with its measured values of magnetic parameters. Experimental results indicate that, if the training dataset has sufficient samples, the proposed method will have a very high accuracy to estimate hardness of the sample, nondestructively.