Remote nondestructive evaluation technique using infrared thermography for fatigue cracks in steel bridges

Long‐standing infrastructure is subject to structural deterioration. In this respect, steel bridges suffer fatigue cracks, which necessitate immediate inspection, structural integrity evaluation or repair. However, the inaccessibility of such structures makes inspection time consuming and labour intensive. Therefore, there is an urgent need for developing high‐performance nondestructive evaluation (NDE) methods to assist in effective maintenance of such structures. Recently, use of infrared cameras in nondestructive testing has been attracting increasing interest, as they provide highly efficient remote and wide area measurements. This paper first reviews the current situation of nondestructive inspection techniques used for fatigue crack detection in steel bridges, and then presents remote NDE techniques using infrared thermography developed by the author for fatigue crack detection and structural integrity assessments. Furthermore, results of applying fatigue crack evaluation to a steel bridge using the newly developed NDE techniques are presented.     

Quantile POD for nondestructive evaluation with hit--miss data

Probability of detection (POD) is commonly used to measure a nondestructive evaluation (NDE) inspection procedure’s performance. Due to inherent variability in the inspection procedure caused by variability in factors such as crack morphology and operators, it is important, for some purposes, to model POD as a random function. Traditionally, inspection variabilities are pooled and an estimate of the mean POD (averaged over all sources of variability) is reported. In some applications it is important to know how poor typical inspections might be, and this question is answered by estimating a quantile of the POD distribution. This article shows how to fit and compare different models to repeated-measures hit--miss data with multiple inspections with different operators for each crack and shows how to estimate the mean POD as well as quantiles of the POD distribution for binary (hit--miss) NDE data. We also show how to compute credible intervals (quantifying uncertainty due to limited data) for these quantities using a Bayesian estimation approach. We use NDE for the detection of fatigue cracks as the motivating example, but the concepts apply more generally to other NDE applications areas.     

Displacement discontinuity method applied to nondestructive testing related stress problems

A numerical stress analysis technique using the displacement discontinuity method (DDM) is used to evaluate surface breaking and near surface flaws. DDM is described briefly, with the main body of the work devoted to exploring the use of DDM in a nondestructive evaluation (NDE) program. DDM is a subset of boundary element method technique, and it requires that only the boundaries of the problem be described. Two smooth subsurface voids are investigated. Results for two-dimensional circular and elliptical holes are presented. Comparisons with experimental and theoretical work are shown. The method of uneven element spacing is explored. The results are examined in the context of providing information for NDE inspection requirements and the definition of acceptable flaws. DDM is very well suited for examining the stress field around a surface crack. Surface cracks can be very dangerous and good NDE inspection techniques are required. A method of obtaining the stress intensity factors is developed and illustrated on angular surface breaking cracks. The results are compared with limited experimental and numerical results and interpreted in terms of NDE inspection requirements.     

On the application of moment methods to electromagneticnondestructive evaluation

The application of moment methods (MMs) to eddy-current testing problems for nondestructive evaluation (NDE) is considered. A general formulation for the MM that can be used to analyze NDE problems is derived, and calculated results and experimental data obtained from eddy-current testing of an artificially made sample are presented. Good agreement between the calculated results and the experimental data confirms the validity of the method and shows that the MM can be used as an alternative to the finite-element method (FEM) and the boundary-element method (BEM) in NDE     

Comparison of Dynamic Young’s Modulus of Thin Concrete Disks to Stress Wave–Based Nondestructive Evaluation Findings

Stress wave–based nondestructive evaluation (NDE) techniques are frequently used for in-situ evaluation of concrete. Stress wave velocity in a material is related to Young’s modulus of elasticity. Cores for in-situ compressive strength are subject to a minimum length-to-diameter ratio requirement that enforce large specimen sizes. Thin circular disks sawn from cylinders or cores are widely used in measurement of chloride or air permeability of concrete. While these methods provide useful information on concrete properties with depth, the capability of measuring changes in mechanical properties such as elastic Young’s modulus in small depth increments is of value to both researchers and consulting engineers conducting condition assessment or NDE, particularly when damage gradients exist. Changes in properties over relatively small depths may be undetected otherwise due to limitations of test method, equipment, or imposed specimen size. This study presents applications of Young’s modulus of thin concrete disks to structural assessment projects involving damage and damage gradients. In-situ nondestructive ultrasonic pulse velocity (UPV) testing was used in identification of affected areas. Young’s modulus of thin concrete disks was used in interpretation of the NDE results and provided an improved understanding of the extent of damage that was indicated using NDE. Two different case studies are discussed: exposure to fire and exposure to thermal shock and cryogenic temperatures. The use of thin disks enabled determination of mechanical properties of relatively thin layers of concrete and, therefore, provided a means to quantitatively assess the extent of damage gradients. Confirmation of NDE results using modulus data and analytical modeling using the relationship between Young’s modulus and pulse velocity provided improved understanding of NDE findings reducing uncertainty in engineering analysis and improving repair recommendations.     

NDE in aerospace-requirements for science, sensors and sense

The complexity of modern NDE (nondestructive evaluation) arises from four main factors: quantitative measurement, science, physical models for computational analysis, realistic interfacing with engineering decisions, and direct access to management priorities. Recent advances in the four factors of NDE are addressed. Physical models of acoustic propagation are presented that have led to the development of measurement technologies advancing the ability to assure that materials and structures will perform a design. In addition, a brief discussion is given of current research for future mission needs such as smart structures that sense their own health. Such advances permit projects to integrate design for inspection into their plans, bringing NDE into engineering and management priorities. The measurement focus is on ultrasonics with generous case examples. Problem solutions highlighted include critical stress in fasteners, residual stress in steel, NDE laminography, and solid rocket motor NDE.     

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.     

Three-Dimensional Localization of Defects in Stay Cables Using Magnetic Flux Leakage Methods

The application of magnetic flux leakage (MFL) methods to the nondestructive evaluation (NDE) of metal parts has been known for several decades. The inspection of large-diameter cables (Ø 100 mm), such as bridge stay cables, is a new field of application for the MFL method. The large cross-section of the cables requires the generation of strong magnetic fields in order to obtain the induction fields necessary for an accurate inspection of the cables. A new device for the inspection of stay cables has been developed in order to meet the requirements given by the size of the cables. Measurements performed with the developed device on full-scale specimens in the laboratory and first calculations confirm the validity of the MFL approach to the inspection of bridge stay cables. The equipment was used satisfactorily in 2001 for the NDE inspection of the 68 locked coil stay cables (121 mm < Ø < 167 mm) of a bridge in Southeast Asia. For such cables, no exact localization within the cross section was performed. Thus far, an accurate indication of the position of the detected flaws along the length of the cables could be given. A qualitative statement about position and size of the flaws within the cross section of the cable could also be made. Given the large steel cross-section of the cables, no other nondestructive method to confirm the findings could be applied to assess the exact size and position of the detected flaws. The proposed analytical method presented in this paper makes it possible to increase the amount of information that can be extracted from the measured MFL data with regard to the exact location of the detected flaws within a cross section of a stay cable.     

In-situ cracking for nondestructive inspection process validation

ork at the Idaho National Engineering and Environmental Laboratory (INEEL) includes efforts to weld steel storage containers. Producing repeatable high quality welds and assuring weld quality is paramount to this work. The nondestructive examination (NDE) method used to measure weld quality is the magnetic particle testing (MT) process since the containers are fabricated from mild steel. A paradox occurred during the initial mockup welding and inspection system demonstrations. Since the welding was flawless, the semi-automatic remote MT system had no defects to find. The MT system was calibrated, as per the welding code, with calibration blocks, but it never demonstrated that it worked during the demonstration because of the flawless welds. To validate the MT system during the mockup welding demonstration, in-situ defects were artificially generated. Two-in. (5.1-cm) long copper wire segments were placed into the weld groove joint and consumed into the weld metal during welding. This in-situ crack generation technique provided physical defects for the inspector/regulator to observe, which then validated the inspection system.     

闪烁陶瓷材料的研究进展

闪烁陶瓷是一种应用在核医学、高能物理、材料无损探伤、安全检查、地质勘探等领域的新型功能陶瓷材料.综述了近年来研究和开发的闪烁陶瓷的性能、发光机理及其应用,以及闪烁陶瓷的发展方向.     

Quantitative Detection of Internal Defects in Automotive Tires by an Interferographic Technique

Because of to the advantages of high sensitivity, nondestructive evaluation, and whole-field analysis, the interferographic technique is superior to other nondestructive evaluation (NDE) techniques. In this article, precut cracks 25 mm and 40 mm long that did not cut through the tire and that extended in different directions inside the tire were made. The interference fringes caused by the tire cracks under different pressures were obtained. By applying the proposed intensive characteristic model to the tires with internal defects, the position, length, and direction of the cracks can be evaluated. Results showed that the errors of experimental data are in good agreement; all were less than 7.6%.     

Crack Characterization Method with Invariance to Noise Features for Eddy Current Inspection of Fasterner Sites

There is a need for research in eddy current (EC) nondestructive evaluation (NDE) to improve the reliability to detect, locate and size cracks around fastener sites in multi-layer structures while minimizing the overall cost of inspection. The objective of this work is to develop feature extraction and classification algorithms for crack characterization with invariance to noise features for eddy current inspection of fastener sites. Model-based parametric studies were first performed to explore potential features under a wide array of crack, noise and material conditions. Through these studies, several features were identified to have some invariance to the characteristic asymmetric response due to gaps between the fastener and hole, probe liftoff variation, and probe skew. In particular, a promising feature with noise invariance to all non-flaw conditions considered in this study was found through investigating changes in the eddy current response along a circumferential direction in an annulus region away from the hole center. To obtain a measure of this localized crack feature, an approach was developed using a fit of a characteristic function to the data through nonlinear least squares estimation. A model-based optimization approach was also implemented to evaluate the best signal processing algorithm design to distinguish between several classes of crack size. Using this approach, an optimized measure was found to be well correlated with subsurface crack size and insensitive to noise conditions included in this study.     

Temperature recovery and contrast computations in NDE thermographic imaging systems

Thermographic imaging systems find application in many nondestructive evaluation problems. However, because of the inherent nature of the image-formation process, several degradations arise which preclude a more generalized use of thermographic NDE. In this paper, we analyze radiometric and noise degradations and propose a calibration process for the imaging systems which allows recovery of object surface temperature evolution. Moreover, a constrast computation technique which combines both the time and spatial reference techniques is shown to increase the defect visibility and make possible a more quantitative (sizing) defect evaluation.     

Pulse-echo microwave imaging for NDE of civil structures: Image reconstruction,enhancement, and object recognition

This article presents an overview of the application of microwave imaging in nondestructive evaluation (NDE) of civil structures. The presentation includes the image formation algorithm operating in monostatic multiple-frequency mode, resolution enhancement by wavefield statistics, and object recognition procedures. Results from theoretical analysis, laboratory experiments, and full-scale field tests are discussed sequentially. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 407–412, 1997     

Investigation of Uncooled Microbolometer Focal Plane Array Infrared Camera for Quantitative Thermography

Thermal nondestructive evaluation has shown promise as a potential NDE technology for next generation US Army rotorcraft structures because it is rapid, noncontacting, and able to inspect complex geometries. To successfully apply thermal inspection systems for field use, the cost and size must be lowered. The infrared camera is a major factor contributing to the overall cost of commercially available thermal inspection systems. Recent advances in uncooled microbolometer focal plane array detectors have resulted in low cost, small size/weight, and low power consumption cameras. These attributes make this technology well suited for portable low cost thermal inspection systems. The purpose of this paper is to investigate the capabilities of the new microbolometer infrared cameras for quantitative thermal nondestructive evaluation. Quantitative thermal diffusivity and thickness images are obtained by minimizing the squared difference between the data and a thermal model on samples with fabricated defects. Critical infrared camera features such as spatial and temperature resolution, detector response time, and detector stability are studied by comparing results to a conventional thermal imaging camera using a cooled InSb focal plane array detector. Finally several techniques are presented to improve the camera’s performance. These techniques include temporal background subtraction, use of a synchronized electronic shutter system, and cyclic flash heating.     

Accept/reject decisions and failure prediction for structural ceramics: Application to failure from voids

A general probabilistic method for reaching accept/reject decisions and failure prediction based on nondestructive evaluation procedures is described. The method is illustrated for ceramic materials that fail by the activation of microcracks located at void surfaces. The inspection procedure used for the analysis is the long wavelength ultrasonic method. The analysis indicates influences on the decision level and on the false-reject probability of variations in the signal-to-noise ratio and in the preexistent void population. The ultrasonic inspection is shown to exert a relatively minor influence on the false-reject probability, even for low signal-to-noise ratios, low stresses, and a widely dispersed void population, because of the intrinsic variability of the selected failure process. More encouraging results concerning the utility of NDE are anticipated to apply to other failure mechanisms in ceramics.     

Fiber optic sensing for ultrasonic NDE

An innovative approach to nondestructive evaluation (NDE) using noncontacting optical sensors has demonstrated. In this effort a single mode optical fiber interferometer (OFI) was used to sense the presence and form of Rayleigh waves traveling along the surface of a steel test bar at a velocity of nearly 3mm/µs. Acousto-optic time-domain data was successfully used to detect the presence and locate the position of a test flaw (a machined slot) in the bar, and spectrum analysis was used to estimate its geometry and size. This approach has many potential applications in the ultrasonic evaluation of real flaws in structures with complex geometries. Coupled with the authors' earlier work demonstrating the feasibility of generating acoustic waves in metals using laser light pulses transmitted through the fiber optic probes, this latest achievement points to the development of a fully noncontacting, fiber optic based thermal-acousto-photonic (TAP) NDE system, with potential applications to the reliability testing of many important structures where composition, scale, geometry, or restricted access preclude the use of conventional NDE techniques.     

Adaptive Cross Approximation Algorithm for Accelerating BEM in Eddy Current Nondestructive Evaluation

This paper presents the adaptive cross approximation (ACA) algorithm to accelerate boundary element method (BEM) for eddy current nondestructive evaluation (NDE) problem. The eddy current problem is formulated by boundary integral equation and discretized into matrix equations by BEM. Stratton–Chu formulation is selected and implemented for the conductive medium which does not has low frequency breakdown issue. The ACA algorithm has the advantage of purely algebraic and kernel independent. It starts with hierarchically partitioning the object to get diagonal blocks, near blocks and far blocks. The far-block interactions which are rank deficient can be compressed by ACA algorithm meanwhile the elements for diagonal-block interactions and near-block interactions are stored and computed by BEM. We apply modified ACA (MACA) for more memory saving while keeping almost same accuracy compared with original ACA. For numerical testing, several practical NDE examples such as coil above a half space conductor, tube in a fast reactor and Testing Electromagnetic Analysis Methods (TEAM) workshop benchmark problem are presented to show the robust and efficiency of our method. With the aid of ACA, for electrically small problems, the complexity of both the memory requirement and CPU time for BEM are reduced to \( O\left( {N\log N} \right). \)     

Radiographic inspection in failure investigations

This article is an introduction to one of the most commonly used and infrequently discussed techniques applied to failure investigations—industrial radiography. Radiographic testing or inspection (RT) is a rapid, nondestructive evaluation process that can provide critical information in the early stages of a failure analysis. Its application is not limited to metallurgical investigations, but also complements electrical, fire causes and origins, and general mechanical investigations.     

ProSINTAP – A probabilistic program implementing the SINTAP assessment procedure

Within SINTAP, a probabilistic procedure has been developed by SAQ Kontroll AB. The procedure can be used to calculate failure probabilities under two conditions: when a defect size is obtained from non-destructive testing (NDT)/non-destructive examination (NDE) or when no defect is detected by NDT/NDE.A computer program based on this procedure, ProSINTAP, has been developed. This program is also able to estimate partial safety factors from the input target failure probability and characteristic values for fracture toughness, yield strength, tensile strength and defect depth. Extensive validation has been carried out, using the computer programs from Nuclear Electric and from SAQ Kontroll AB.