Nondestructive Evaluation System Research Articles

Analytical Model for the Extraction of Flaw-Induced Current Interactions for SQUID NDE

Incorporating an analytical approach to simulate the interaction of a series of long cracks and the induced current of a double-D excitation coil, we have developed a model-based method to do precise detection of the positions of the cracks in a metallic structure by using eddy-current superconducting quantum interference device (SQUID) nondestructive evaluation (NDE) measurements. Conventionally, the structure of the defects is found by iteratively solving a numerical forward problem, which is usually based on finite-element, boundary-element, or volume-integral method. This, however, incurs a heavy numerical burden, as every time the forward problem is to be solved, a rigorous numerical model should be inevitably employed to extract the complex distribution pattern of the induced current encountering defects of the structure. In this paper, an analytical approach is used for the modeling of the interaction of the induced current and a series of cracks in the sample. It duly considers the distribution of the induced current in the flawed samples, does not call for extremely high computational resource, and thus permits efficient NDE as the forward problem can be solved within a reasonable time. Here, a high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Tc</i> first-order radio-frequency SQUID gradiometer is employed as the magnetic sensor of the NDE system to scan the samples with different cracks. The accuracy of the proposed algorithm is verified by having the extracted shape of the defects obtained by applying the proposed algorithm on the SQUID NDE measurements against the actual cracks.

Nondestructive Evaluation of Naval Munitions Using X-Ray CT

In this manuscript, we present experimental results from a nondestructive evaluation (NDE) system that is being used to inspect naval munition components, such as missile rocket motors. The X-ray computed tomography–based NDE (CT-NDE) system was developed by the NDE group at the Indian Head Division, Naval Surface Warfare Center (NSWC) in Indian Head, MD. The maximum likelihood (ML) method has been used successfully to reconstruct transmission images in a medical imaging modality known as positron emission tomography. Motivated by this fact, we use the ML method to reconstruct transmission images for the CT-NDE system at the Indian Head Division, NSWC and investigate its performance using experimental studies. From these studies, we preliminarily conclude that the ML method reconstructs transmission images with good quantitative accuracy and significant detail, even when there is limited angular sampling.

Composite non-destructive evaluation system for probability of detection assessment

In non-destructive evaluation (NDE) studies, the probability of detection (POD) curve is an important performance metric for an NDE system. POD curve estimation and NDE capability assessment are based on the flaws detected and the flaws missed. In order to get the information of undetected flaws, fabricated artificial flaws are often used which provide complete information of defects in most of laboratory demonstrations. However, this practice is too expensive and impractical to use in the field environment. In this study, a combination of several additional NDE inspection systems, called composite NDE system, is proposed to assist the POD evaluation based on field inspection. A simulation model is built to evaluate the effectiveness of the composite NDE system. The simulation result of this approach is verified and compared with traditional POD evaluation methods.

A multi-mode structural health monitoring system for wind turbine blades and components

The Adverse Event Detection (AED) system described in this paper supports nondestructive evaluation (NDE) systems and evaluates advanced composite structures such as wind turbine blades. AED is a joint effort by Extreme Diagnostics and Virginia Polytechnic Institute and State University (Virginia Tech). AED uses the impedance method to monitor bulk structural integrity, wave propagation methods to assess surfaces, and acoustic emission (AE) structural health monitoring (SHM) to detect adverse events such as impacts. The incorporation of AE methods significantly increases the sensor coverage area, which is crucial in health monitoring of large-scale structures like wind turbine blades. Our AED system provides on-line assessment of structural integrity during normal operations, as opposed to traditional nondestructive evaluation (NDE) methods that are commonly applied off-line—that is, systems must be shut down for inspection by conventional NDE. Our AED system not only provides timely information during operation, it can also reveal defects that only become apparent under operational stress—such defects can be overlooked by traditional off-line inspection methods. AED actively examines structures across several length and time scales in an autonomous fashion, thus greatly reducing the number of sensors required and lowering system complexity and cost. Our early AED prototype demonstrated impedance-based SHM in wind turbine blades. This project integrates three previously independent SHM approaches, and demonstrates damage detection on a composite structure. Our current AED prototype is a low-power, wireless, and embeddable sensor that detects incipient damage in near real-time and automatically provides early warning of structural damage. Our AED system is also suited to a variety of aerospace applications that include composite overwrapped pressure vessels. AED also supports Homeland Security, and furthers national preparedness by monitoring infrastructure integrity and disaster response by providing damage assessment.

Optimum eddy current excitation frequency for subsurface defect detection in SQUID based non-destructive evaluation

Detailed experimental studies have been carried out for the determination of optimum eddy current excitation frequencies for the defects located at different depths below the top surface of an aluminum plate. These subsurface defects were detected by using a highly sensitive superconducting quantum interference device (SQUID) based eddy current non-destructive evaluation (NDE) system. The signal to noise ratio was found to be significantly higher at the optimum excitation frequency, which depended on the depth of the defect. The optimum excitation frequencies have been evaluated for defects located at different depths from 2 to 14 mm below the top surface of the plate. The defect depth was varied in steps of 2 mm, while the overall total thickness of the stack of plates was kept constant at 15 mm. Each defect represented a localized loss of conductor volume, which was 60 mm in length, 0.75 mm in width and 1 mm in height. The experimental results show that the square root of the optimum excitation frequency is inversely proportional to the depth of defect.

Aircraft Wing Inspection Based on Anomalous Wave Propagation Imaging

Non-destructive evaluation (NDE) and structural health management (SHM) with the ability to evaluate the severity of a damage are important to ensure the reliability of a structure. We propose a local non-destructive evaluation (NDE) system based on Anomalous Wave Propagation Imaging (AWPI) method. When possible damage is flagged during the lifecycle of the structure, the proposed system will be launched for automatic damage evaluation. This technology was demonstrated on a CFRP skin-spar-stringers wingbox integrated with an AE sensor. 17 mm diameter impact damage was made between the stringers using hammer strike from outer surface of the skin. Based on the impact location determined by other global structural health monitoring system, the AWPI automatically inspects an area 400×400 mm2 with the impacted location enclosed. Anomalous Wave Propagation Movie (AWPM) was generated as inspection result. As contrast to its predecessor, the AWPM shows only the damage induced ultrasonic wave (anomalous wave), making the damage detection an intuitive decision making process. Precise damage localization was performed by identifying the location of area with anomalous wave propagation in the AWPM. Besides, the size of the area with anomalous wave agreed well with the size of impact damage, which demonstrated that damage size quantification is possible using the proposed system. Being sensitive only to anomalous wave, it is expected that this NDE system is exceptionally suitable not only for aircraft structures such as wingbox with stiffeners, but also for other complex engineering structures.

Nondestructive Evaluation of Braided Carbon Fiber Composites Using High Tc SQUID

Braided carbon fiber reinforced plastics (CFRP) is one of the multifunctional materials for applications to industrial products. We applied the superconducting quantum interference devise (SQUID) nondestructive evaluation (NDE) technique with high magnetic sensitivity and spatial resolution to inspect the state of the fabric in the braided CFRP. We prepared flat braided CFRP samples with nonuniform, uniform and cut-out bundles, which were fabricated with fold biaxial (±45º) tubular fabric and epoxy resin. While injecting ac current into each sample, the diagonal magnetic field gradients dBz/dx and dBz/dy above each sample were measured by the NDE system employing a SQUID gradiometer and xy-scanning stage, and then, the current flow in each sample was visualized by the field-gradient-to-current conversion method. In the measurements, it was shown that the current flowed along the continuous bundles in the cases of nonuniform and uniform samples, and it transmitted between bundles in the case of the sample with cut-out bundles. From these results, we showed the possibility that the NDE method can be applied to the nondestructive inspection of the integrity of the textile of braided CFRP.

Evaluation of joint interface of friction stir welding between dissimilar metals using HTS-SQUID gradiometer

In this study, we investigated conductive properties of joint interfaces of friction stir welding (FSW) between dissimilar metals, stainless steel SUS304 and aluminum A6063, using a SQUID nondestructive evaluation (NDE) system. With current injection method, the current maps above the FSW specimens jointed under various conditions were measured by a HTS-SQUID gradiometer. The conductivities of the joint interfaces, which were estimated from the current maps, differed between the joint conditions. By destructive tests using optical microscope, large voids were observed on the joint interfaces with low welding speed that generated excess heating. In case of one specimen, which was welded with welding speed of 500 and 200mm/min, the conductivity of the former was higher than that of the latter, although the inside voids in the respective regions were not much different. From these results, it is suggested that the current maps were influenced not only by the conductivity of the joint interface but also by inside voids. By hardness test on the SUS boards near the interfaces, only the SUS jointed with 200mm/min was about half softer than its matrix.

An Efficient Finite-Element Approach for the Modeling of Planar Double-D Excitation Coils and Flaws in SQUID NDE Systems

Incorporating an efficient approach for the finite-element simulation of eddy current superconductive quantum interface device (SQUID) nondestructive evaluation (NDE) systems, an appropriate finite-element method (FEM) has been presented for simulating and analyzing such systems. We have introduced a new model for the planar double-D coils, which are used as the excitation source in eddy current SQUID NDE systems, and also another model for the description of the flaw effect on the induced current. We have also examined our simulation results with their associated measurements. Our system is based on a high-TC YBCO gradiometer RF-SQUID sensor with a flux noise level below 100 ??0/ ?Hz at 100 Hz in an unshielded environment while being shielded against external RF electromagnetic interference. The very good agreement between experimental and numerical approaches confirmed our model for the 3-D FEM simulation of the system, which is being done in reasonable time and using reasonable computer resources.

Spatial Recognition of a Superconducting Quantum Interference Devices Nondestructive Evaluation System Using a Small Room-Temperature Probe

A superconducting-qantum-interference-device (SQUID) nondestructive evaluation (NDE) system using a small room-temperature probe is developed for active scanning rather than for a massive movement occurring in a traditional SQUID NDE system. The small room-temperature probe is composed of a quadruple excitation coil and a double D-shaped pickup coil. It is connected to the input coil surrounding a high-Tc rf SQUID, immersed in liquid nitrogen, and shielded by a shielding can. Beyond the NDE function, the SQUID NDE scheme has spatial recognition functions, including the detection of the orientation and depth of a narrow line crack using different parameters, and the scanning of images of large objects with arbitrary shapes. Furthermore, the spatial sensitivity, limited by the size of the probe, reaches up to only 7 µm in the aspect of crack widths and 1 mm in the aspect of spatial intervals for precision NDE on a printed circuit board.

Activities on risk-informed in-service inspection within the ENIQ network

The European Network for Inspection and Qualification (ENIQ) is a utility-driven network that works towards a harmonised European approach on reliable and effective in-service inspection (ISI), primarily in the nuclear power industry. The ENIQ has two task groups: a Task Group on Qualification (TGQ), which works on issues related to the qualification of non-destructive evaluation (NDE) systems, and a Task Group on Risk (TGR), which is focused on risk-informed in-service inspections (RI-ISI). After publishing the European Framework Document on RI-ISI in 2005, ENIQ TGR has been working on producing more detailed recommended practices and discussion documents on several RI-ISI related issues. The following reports have been issued: (1) Discussion document on the role of ISI within the philosophy of defence in depth; (2) Recommended practice on verification and validation of structural reliability models (SRMs) and associated software to be used in RI-ISI programmes; (3) Recommended practice on guidance on expert panels in RI-ISI; (4) Discussion document on application of RI-ISI on reactor pressure vessel. Work is ongoing to develop a discussion document on the updating of RI-ISI programmes and new initiatives were recently launched to study topics such as what magnitude of risk reduction is reasonable to achieve through ISI, how to set inspection targets following the selection of ISI sites and how to produce detection probability estimates for ISI. In addition, TGR has been active in initiating international projects linked closely to its work, such as the JRC-OECD/ NEA co-ordinated RI-ISI benchmark exercise (RISMET) and the project on the relation between inspection qualification and RI-ISI. The aim of this paper is to review and explain these activities of ENIQ TGR.

Miniature Mobile Sensor Platforms for Condition Monitoring of Structures

In this paper, a wireless, multisensor inspection system for nondestructive evaluation (NDE) of materials is described. The sensor configuration enables two inspection modes-magnetic (flux leakage and eddy current) and noncontact ultrasound. Each is designed to function in a complementary manner, maximizing the potential for detection of both surface and internal defects. Particular emphasis is placed on the generic architecture of a novel, intelligent sensor platform, and its positioning on the structure under test. The sensor units are capable of wireless communication with a remote host computer, which controls manipulation and data interpretation. Results are presented in the form of automatic scans with different NDE sensors in a series of experiments on thin plate structures. To highlight the advantage of utilizing multiple inspection modalities, data fusion approaches are employed to combine data collected by complementary sensor systems. Fusion of data is shown to demonstrate the potential for improved inspection reliability.

Laser ultrasonic surface wave dispersion technique for non-destructive evaluation of human dental enamel

This paper describes a novel optical system for clinical diagnosis of dental enamel based on its elasticity. Current examination techniques are typically destructive, and frequently impractical for in-vivo inspection. This paper describes the first application of a laser ultrasonic non-destructive evaluation (NDE) method for clinical dental diagnosis. It performs remote elasticity evaluation on small dimension samples. A focused laser line-source generates broadband surface acoustic wave (SAW) impulses which are detected with a simplified optical fibre interferometer. The measured SAW velocity dispersion spectrum was in turn used to characterise the elasticity of the specimen. Different metal structures were measured to verify the system performance. The results agree well with theoretical values and confirm the reliability and accuracy of the laser NDE system. This technique was then applied to evaluate the surface of sound natural human dental enamel. The measured dispersion spectra match theoretical expectations and the influences of both the enamel and the underlying dentin on the surface wave propagation were observed. This is the first time, to the best of our knowledge, that a laser based SAW velocity dispersion technique has been successfully applied on human dental enamel. As a remote, non-destructive technique it is applicable in-vivo and opens the way for early diagnosis of dental caries.

Optimization of NDE Characterization Parameters for a RF-SQUID Based System Using FEM Analysis

We have investigated the dependence of the optimal non destructive evaluation (NDE) characterization on different excitation parameters in an eddy current SQUID NDE system for samples with known flaw depths. The considered parameters in our study include the configuration of the excitation-coil and its current frequency. The system is based on a high-TC YBCO gradiometer RF-SQUID sensor with a flux noise level below 100 muPhi0/radicHz at 100 Hz in an unshielded environment, while being shielded against external RF EMI (electromagnetic interference). According to experimental results and the associated numerical analysis using finite element (FEM) simulations, we have derived the optimized parameters for the maximum sensitivity of the system. The optimized parameters are found using a new model for excitation coil and eddy current anomalies caused by the flaws. Very good agreement between experimental and numerical approaches confirmed our model and the resultant implemented optimization method.

NDE of coated-conductor using HTS SQUID array

We developed a non-destructive evaluation (NDE) system using an HTS SQUID array in order to examine rare-earth (RE)-123 HTS coated conductors striated into multi-filamentary lines. The 5-channel HTS SQUID gradiometer array was composed of ramp-edge junctions with LaErBaCuO and SmBaCuO electrode layers, and fabricated by using an HTS multi layer fabrication technique. The planar gradiometers with 1 × 1 mm 2 pickup loops and a baseline of 1 mm detected the vertical element of magnetic field gradient induced around defects by an eddy current. The gradiometer array cooled by thermal conduction from a liquid nitrogen bath was placed above the coated conductor on the main stage with a lift-off of about 1.5 mm. A coated conductor was fed from a reel to reel, and cooled blow its T c by stages connected to Gifford–Mcmahon (GM) coolers. By employing a 3 kHz induction current generating the maximum field of 0.14 mT, we could identify a distribution of defects in a long-length non-striated conductor. Furthermore, we could detect and distinguish three kinds of defects, existence of a spotty normal-state region, electrical short between striated filaments, and delamination of the superconducting layer from the Hastelloy tape for each filamentary superconducting line at a high speed up to 30 m/h.

Noncontact, nondestructive elasticity evaluation of sound and demineralized human dental enamel using a laser ultrasonic surface wave dispersion technique

Laser ultrasonic nondestructive evaluation (NDE) methods have been proposed to replace conventional in vivo dental clinical diagnosis tools that are either destructive or incapable of quantifying the elasticity of human dental enamel. In this work, a laser NDE system that can perform remote measurements on samples of small dimensions is presented. A focused laser line source is used to generate broadband surface acoustic wave impulses that are detected with a simplified optical fiber interferometer. The measured surface wave velocity dispersion spectrum is in turn used to characterize the elasticity of the specimen. The NDE system and the analysis technique are validated with measurements of different metal structures and then applied to evaluate human dental enamel. Artificial lesions are prepared on the samples to simulate different states of enamel elasticity. Measurement results for both sound and lesioned regions, as well as lesions of different severity, are clearly distinguishable from each other and fit well with physical expectations and theoretical value. This is the first time, to the best of our knowledge, that a laser-based surface wave velocity dispersion technique is successfully applied on human dental enamel, demonstrating the potential for noncontact, nondestructive in vivo detection of the development of carious lesions.

The characterization of a sensitive room-temperature probe for use in a SQUIDnondestructive evaluation system

In this work, a SQUID nondestructive evaluation (NDE) system withoutstanding mobility and performance is developed using two units connectedby copper wire. One of those units is a SQUID unit consisting of ahigh-Tc SQUID as well as a surrounding input coil, which are both cooled in liquid nitrogen andkept in a Dewar shielded by a cylindrical can with a shielding factor of 80–100 dB rangingfrom DC to 1 kHz. The other is a small, room-temperature probe composed of excitationcoils and pickup coils. Based on the quadruple excitation field with the advantages of notonly good balance of excitation noise but also a higher field gradient for enhancing themagnetic field distorted by small cracks underneath and a coplanar and differential coilwith good ability to diminish the sensing of the magnetic field in the non-flaw region, thesmall and activated probe is made of quadruple excitation coils distributed indouble D-shape differential pickup coils. The analysis shows that the SQUID NDEsystem using the novel probe design has advantages such as low thermal-noiseintroduction to the SQUID system, high transfer efficiency, efficient balancingof the excitation field as well as the dynamic noise during scanning, and highsensitivity, with a signal-to-noise ration (SNR) of 2 against the noise level of8.5 ± 1.5 pT. This SQUID NDE system with the proposed probe is characterized by cracks withdifferent widths at different depths, for example, fine spatial resolution up to7 µm crack width on the surface of copper foil.

Development of High-T c SQUID System for Nondestructive Evaluation

Nondestructive evaluation (NDE) system with high spatial resolution power based on high-T c superconducting quantum interference device (SQUID) has been developed. The SQUID is fabricated by YBCO thin film and mounted in vacuum at the end of a cold finger fixed at the inner wall bottom of the dewar, which is filled with liquid nitrogen (77 K) to cool the SQUID sensor. The sensor faces a thin flat sapphire window on the outer wall of the dewar and is thermally isolated from it by a vacuum space at a distance of less than 1 mm. The magnetic field sensitivity of SQUID is about 40 pT/ \(\sqrt{}\) Hz in magnetically unshielded environment. This NDE system was used to detect the flaws buried into materials. The remnant magnetic field inducted by the local damages in a stainless steel sample was measured. Incorporated a gradiometric double-D excitation coil, the eddy current NDE was carried out. Small cracks in the aluminum below the surface can be detected effectively in unshielded environment.

Monte Carlo modeling of a cosmic ray imaging system for non-destructive evaluation of a reinforced concrete column

A detailed knowledge of the condition of reinforced concrete columns is essential for the planning of maintenance of a large building. We performed a Monte Carlo simulation to examine how well cosmic-ray muon radiography technique works on non-destructive testing of reinforcing concrete and we found that this technique can be an efficient tool for obtaining information such as the size and depth of reinforcing bars beneath concrete. We examined a concrete column with a cross-sectional size of 559×559 mm 2, reinforced with steel bars of 52 mm diameter, in order to estimate the positioning accuracy. Using simulations of 6 million muons/sr, we found that the precision for bar size measurement is 4.1 mm and that for bar location is 2.5 mm. We describe a possible inexpensive imaging system capable of determining the size and depth of an object and discuss the technique and the benefits of cosmic-ray radiography.

Development of SQUID-Based System for Nondestructive Evaluation

This article describes the development of a superconducting quantum interference device (SQUID)-based system for nondestructive evaluation. The setup incorporates an in-house developed thin-film-based Nb SQUID with readout flux locked loop electronics and consists of a liquid helium cryostat with adjustable stand-off distance, a precision XY- thetas scanner for studying both flat and cylindrical samples, and a data acquisition system. The system has been used for the detection of artificially engineered subsurface defects in aluminum plates and to track magnetic-to-nonmagnetic phase transformation in stainless steel [grade 316L(N)] weldment specimens subjected to low cycle fatigue deformation.