Abstract: The feasibility of detecting anomalies or discontinuities in concrete beams using lamb waves is investigated in this paper. The traditional ultrasonic methods for inspecting discontinuities in concrete use the reflection, transmission and scattering of longitudinal waves by internal discontinuities. Signal amplitude and time of flight measurements provide information about the internal anomalies in concrete. However, these methods are time consuming and, as will be shown in this paper, the traditional techniques often fail to detect honeycombs, closed cracks and small anomalies. In this paper the potential of the lamb wave technique to detect those anomalies in large concrete beams is investigated. The lamb wave technique is found to be reliable for detecting such anomalies.

Abstract: Probability of detection (POD) is traditionally determined by empirical techniques in which a series of specimens containing known discontinuities are examined to assess performance of the test, as influenced by a number of factors including the test system and operator. Although this approach has proven quite useful over the last three decades, it suffers from the fact that a new set of specimens are traditionally fabricated and tests conducted whenever new test procedures or part geometries are to be tested. This can be both a costly and time consuming process. During this same period there has been a steady increase in the ability of physical models to accurately predict the results of tests of real parts and in the ability to make rapid computer based simulations based on these models. The opportunity now exists to incorporate such simulations in new procedures for POD determination that reduce these time and cost constraints. A modular approach is described that combines the ability of simulations to predict physical phenomena that are well understood with empirical measurements where such understanding does not exist. Examples of recent work is given for the case of ultrasonic testing, as well as indications of some current directions in the areas of eddy current and X-ray testing.

Abstract: Nondestructive testing (NDT) of high temperature coatings is one of the important factors in achieving a high level of structural integrity in advanced gas turbines. In this paper, we demonstrate that sophisticated eddy current techniques can be utilized to measure the thickness and remaining life of high temperature coatings. Some research has been conducted to apply such techniques to the preservice case, for which the coating has one nicely defined layer and nothing of consequence has diffused into the base metal that would create additional layers of anomalous material. We discuss the much more difficult inservice case, in which the time temperature exposure of the combustion turbine blade has created a four layered system, in addition to the base metal.

Abstract: The object of ultrasonic nondestructive testing (NDT) is to find anomalies using nondestructive methods. Block filtering and deconvolution are the most commonly used digital signal processing methods for improving the resolution of ultrasonic images. However, if the anomaly is not a horizontal plane anomaly, these methods cannot correct the distortion and mislocation of the anomaly image. The Kirchhoff migration is an image processing method, currently used as the most basic and important procedure for data processing of seismic exploration. It is also the simplest unlimited migration method. This method can improve the image resolution and recover the true shape and location of an anomaly's image. This research used the Kirchhoff migration method to process ultrasonic images. The experimental results show that the Kirchhoff migration method can be used successfully to process both 2D and 3D ultrasonic images. This method clearly improves the image resolution and represents the anomaly's shape, size and location more accurately.

Abstract: Due to geometric complexity and flexural mode conversion in pipe elbow regions, guided wave detection of a discontinuity either in the elbow region or beyond is usually difficult, especially when only partial loading around the circumference of the pipe is possible. The signals from the discontinuities are either low in energy or immersed into the weld echoes in the elbow region. A new flexural mode tuning technique to find discontinuities in the elbow region by amplifying the discontinuity signal and improving the subsequent signal to noise ratio is introduced in this paper. Flexural mode tuning can be accomplished by a staggered spacing of angle beam transducers around the pipe or by circumferential time delay profiles applied to the multielement angle beam transducers or segmented comb elements mounted in the plane around the circumference of the pipe. Experimental results indicate the potential of this method for finding the discontinuities both at the outside and the inside region of the elbow.

Abstract: Weep holes in C-141 aircraft have been found to be locations for the initiation of fatigue crack growth. Eddy current testing of weep holes in C-141 aircraft requires fuel tank entry by a technician and is a costly and time consuming process. This paper describes the implementation of a neural network assisted, automated ultrasonic testing technique from the outside of the wing. Toward achieving this goal of field implementation of an automated testing technique, this work demonstrates the value of numerical simulation, laboratory studies and algorithm training with samples representing infield variation, infield demonstration, parametric sensitivity studies and probability of detection (POD) validation. The testing capability for the automated procedure was found to exceed both the defined testing requirements and the ability of testing through viewing C-scan images. Field implementation would eliminate the fuel tank entry requirement, drastically reduce weep hole testing costs for the US Air Force and reduce detection variability between technicians in making classification calls.

Abstract: Conventional methods of ultrasonic testing utilizing time domain measurements are seldom capable of detecting microfatigue cracks. Hence, there is a need to conduct amplitude measurements and frequency domain analyses to enhance the sensitivity of the ultrasonic technique. A review of the literature has revealed the difficulty in obtaining the repeatable signals which are necessary for amplitude and frequency analyses. This paper presents a methodology to optimize several factors to produce repeatable signals with good signal to noise ratios. The paper focuses on the use of rayleigh waves, since fatigue cracks typically originate at or near the surface of the members, Also, the combined use of time and frequency domain analyses for fatigue crack detection in metallic structural members has been presented. The methodology was successfully used on aluminum plates and beams with real and simulated fatigue cracks.

Abstract: This paper describes an optical infrared transmission technique to measure the in plane residual stresses in thin single crystal silicon substrates. Fringe multiplication and phase stepping are incorporated to increase the sensitivity of the stress measurement. The measurement is full field and noncontact, and the data processing is automatic. When the fringe multiplication factor of 11 is employed, the measurement sensitivity of the maximum residual shear stress can be 0.4 MPa (58 psi). Both (100) and (111) silicon samples were investigated with this method.

Abstract: Damage tolerant design requires knowledge of reliability in discontinuity detection. Over the last three decades, many nondestructive testing (NDT) reliability assessment and demonstration programs have been performed by various organizations. The subject has substantially evolved in approach, understanding and cost effectiveness. This paper reviews the valuable information available from the past efforts on nondestructive testing reliability.

Abstract: We discuss a new family of local probes that use evanescent, or decaying, electromagnetic fields to image nonuniformities in materials with submicron spatial resolutions at 1 to 10 GHz. These evanescent microwave probes (EMP) map the microwave resistivity of the sample, which is affected by various factors including density, moisture, polymerization, carrier mobility and concentration, impurities, oxidation state and temperature. Using the EMP, we have imaged a variety of organic and inorganic materials including metals, semiconductors, insulators, composites, ferromagnetic materials, tooth enamel, botanical and agricultural samples. The spatial resolution of the EMP was theoretically found to be directly proportional to its tip size and it is strongly affected by the distance to the sample. Experimentally, we have shown in the past that the EMP has a spatial resolution of 0.4 μm (1.6 x 10 -5 in.) wavelength/750 000 at 1 GHz. The main objective of this work is to discuss the overall capabilities of the EMP imaging techniques and their applications.

Abstract: Reliability assessments of nondestructive testing (NDT) techniques are rooted in statistical concepts. However, these concepts are sometimes overlooked, misapplied and misunderstood. Adding to the confusion is the multitude of approaches that often exist in the statistical literature for the same basic problem. This paper reviews fundamental concepts of using regression type data to establish probability of detection (POD) curves. The use of and some common misperceptions about confidence bounds are also discussed. Specific areas of discussion will include components of variation and confidence statements and how these concepts are related to the number of discontinuities in specimen sets and the number and nature of repeat tests.

Abstract: Surface topography is an important variable in the performance of many industrial components and is normally measured with diamond tip profilometry over a small area or by using optical scattering methods for larger area measurement. This article shows quantitative surface topography profiles as obtained using 1 MHz focused air coupled ultrasonic pulses. The profiles were obtained using a system developed by NASA Glenn Research Center and Sonix, Inc., via a formal cooperative agreement. The method is simple and reproducible because it relies mainly on knowledge and constancy of the sound velocity through the air. The air transducer is scanned across the surface and sends pulses to the sample surface where they are reflected back from the surface along the same path as the incident wave. Time of flight images of the sample surface are acquired and converted to depth/surface profile images using the simple relation (d = V x t/2) between distance d, time of flight t and the velocity of sound in air V. In this article, resolution is determined and results are shown for platelike and cylindrical (curved) samples, Impressive results were obtained for all samples when compared with diamond tip profiles and measurements from micro thickness gages. The method is completely nondestructive, noninvasive, noncontact and does not require light reflective surfaces.

Abstract: Ultrasonic guided waves can be generated with great penetration power into a variety of structures including containment structures that are inaccessible by other nondestructive testing (NDT) techniques, The containment structure discussed is a plate partially coated with thick concrete. A transducer is placed near an end section of the plate to produce guided waves in the plate. Anomaly echoes are then received. Several kinds of guided waves including shear horizontal and lamb wave modes were studied in terms of energy leakage, sensitivity and testing reliability. Experimental results show great sensitivity for the anomalies and great penetration ability into the concrete coated plates despite the concrete covering.

Abstract: Researchers have studied the long term durability and quality of concrete structures for many years using several different techniques. One of the most widely used nondestructive techniques for assessing the quality of concrete at a certain age is the ultrasonic pulse velocity (UPV) method. In 1940, the Portland Cement Association started a long term durability study to investigate the effect of variation in cement types on different durability aspects. The sonic vibration method, a precursor to UPV, was one of the methods implemented. The United States Bureau of Reclamation agreed to place 28 different cement types on the parapet wall panels of the Green Mountain Dam. Each of the 28 cement types was used in three or four of the 104 panels of the parapet wall. A complete description of the Green Mountain Dam construction process, aggregate types and cement types used in construction are found in Douglass and McHenry (1947). The Green Mountain Dam is located on the Blue River, a tributary of the Colorado River, 21 km (13 miles) southeast of Kremling, Colorado. The dam itself is an earthfill structure. This particular paper presents results of UPV testing of the parapet wall and analyzes some new trends and further validates some existing trends observed on the velocity of ultrasonic pulses travelling through concrete.

Abstract: In this paper, a method for classifying material types is proposed where wavelets and neural networks are applied on laser speckle images. Multiresolution wavelet analysis was used for feature extraction while neural networks were used for classification. To improve the classifier performance, a reduced set of wavelet coefficients was obtained from all levels of transform resolutions. The effect of the laser angle of incidence on classification sensitivity was investigated. It was found that maximum sensitivity was achieved at an angle of 45 degrees. Results obtained showed that the proposed method was capable of classifying eight different materials from similar and different brands.

Abstract: This paper presents a summary of electromagnetic techniques used for nondestructive testing (NDT) of degradation of nuclear reactor components. Magnetic methods that use direct or low frequency magnetic fields offer a major advantage for field applications. In particular, the use of higher harmonics may provide a valuable NDT method for reactor pressure vessel steels.

Abstract: The objective of the modular approach for measuring the reliability of nondestructive testing (NDT) is to provide a validated testing system that fulfills the requirements of the client in the most efficient and cost effective manner. This capability is especially important where expensive statistical tests are not possible. In developing this concept, a system is divided into appropriate submodules and the discrete reliability of each is tested. The knowledge gained within each of the modules allows an optimization of the total system. The reliability of the total system is then determined by joining the single reliabilities of the modules, including their possible correlation. To facilitate an understanding of the mechanics, the background of reliability analysis is briefly introduced. It is then considered how to properly characterize the reliability of an NDT component. Finally, a first very simple attempt to join the modules is described.

Abstract: The characterization of anomalies found in a waveguide is studied using shear horizontal (SH) guided waves. A boundary element method is used for analysis in examining anomaly shape and size. Experiments with electromagnetic acoustic transducers (EMATs) are reported. Initial comparisons of the numerical and experimental results show good promise.

Abstract: The diagnosis of material degradation and the detection of discontinuities in austenitic cast stainless steel have been studied by using ultrasonic waves generated by an electromagnetic acoustic transducer (EMAT). A simple circuit model for an EMAT generating horizontally polarized shear waves (SH waves) was established and magnitudes of oscillations were estimated by using the model and experimental data. As a result, the attenuation was described at two different frequencies of SH waves.

Abstract: In this paper, the shallow cracks on workpiece surfaces are approximated by the linear magnetic dipoles of finite length. The analytic expression for the magnetic field strength yielded by a linear magnetic dipole of finite length is derived according to Coulomb's law of magnetism. A series of typical curves for the spatial distribution of this magnetic field strength are plotted through the digital calculation whereby the principle of magnetic particle testing for shallow cracks is explained.

Abstract: This article is an overview of the jumpsum method for testing, in a nondestructive manner, the mechanical properties of ferromagnetic materials. The jumpsum method is a magnetic based method, which expresses and analyzes the barkhausen spectrum in terms of its profile rather than assigning the spectrum a mean or root mean square value. The jumpsum methodology allows unambiguous predictions of the mechanical properties of ferromagnetic materials over a wide range, including its ability to detect very small strains that are well below the 0.2 percent offset strain. Micromagnetics of the barkhausen spectrum and hysteresis loops are also discussed.

Abstract: This paper presents an interpretation of dynamic characterization tests aimed at identifying the structural stiffness of ceramic candle filters. The candle filter is a hollow cylindrical structure made of a porous material that protects the gas turbine component in advanced, coal fired power generation systems. A total of 59 ceramic candle filters have been tested nondestructively. All filters were subjected to an excitation force and the response was picked up by an accelerometer in a free-free boundary condition. The experimental results were evaluated using digital signal analysis to obtain the frequency response function and vibration mode shape of each filter. Finite element models were built to calculate the filter's dynamic response. Results from this study indicate that the vibration signatures can be used as an index to quantify the structural properties of ceramic candle filters. The influence of Poisson's ratio on the vibration frequency is minimal. The results also show that the average Young's modulus values obtained for the Coors, Schumacher TF-20 and Refractron 326 filters are about 29.6 × 10 9 Pa (4.3 x 10 6 psi), 42.7 x 10 9 Pa (6.2 x 10 6 psi) and 51 x 109 Pa (7.4 x 106 psi), respectively.

Abstract: Nondestructive testing is often used to make measurements. From the measurements, one infers quantities of interest. If the questions of interest were first phrased in terms of Bayes's theorem, then the processing of the information would reveal the answers directly. Furthermore, by focusing on questions of interest the desired measurements to be taken would be evident. Examples given to illustrate the method are (1) locating a current carrying wire, (2) finding the location of a magnet which is used to tag the movement of soil and (3) detecting the presence of horizontal pipes (or horizontal conducting structures). Each method uses a model or template of the anticipated results to evaluate the item of interest. In all cases, Bayes's theorem is used to answer the question, What is the probability that the question asked is true?

Abstract: The welding acceptance standards for naval ships and submarine pressure hulls indicates that the presence of any incomplete fusion discontinuity in the welds is cause for rejection. In this paper, it is suggested that depending upon the size and location of the discontinuity and the weldment structural transition performance, certain amounts of incomplete fusion are acceptable. In short, weldmetal tearing resistance often overrides the weld discontinuity's influence on weldment failure, In our study, six explosion bulge panels were welded to have severe incomplete fusion discontinuities in weldments which otherwise exhibited low structural transition temperature performance; two panels had root discontinuities and the other four had cap discontinuities. Explosion bulge tests were performed to determine if the welds could resist crack extension beyond the limits of the bulge apex. Prior to explosion testing, the welds were examined with manual and computer aided ultrasonics. They were also radiographed at plus and minus twenty degrees to normal (standard radiography would be shot at normal). The nondestructive testing (NDT) was conducted to relate performance back to NDT (as opposed to just discontinuity size, nature and location). Following explosion testing, the welds were sectioned and opened to determine the true discontinuity nature, size and the degree and nature of extension under explosive loading. Sectioning showed that extension was always by a ductile mechanism for these low structural transition weldments. Based on this work, discontinuity size and location was found to be less of a determining factor in the quality of the weld than the structural transition performance of the weld and steel. It was found that acceptance criteria should be based on whether the structural transition performance is below, within or above the operational envelope, as well as, and not merely, on the size and location of discontinuities.

Abstract: Pipe component testing is required in both the power generation and petrochemical industry. Pipe components include tees and elbows where wall thinning can occur and valves that can have wall thinning as well as internal features of interest. Insulated inservice components are tested today using both ultrasound and radiographic techniques. Film and digital screen radiography are used without insulation removal but they are applicable to a limited range of pipe diameters because of the radiation source intensity and energy. The preferred radiation source for pipe testing is Ir-192 and the thin active layers of film and digital screens have a poor capture efficiency at the energy of iridium gamma ray photons. Industry also uses ultrasound to sample pipe component wall thickness and make estimates of life based on the data. The tests are usually conducted during shut down because the ultrasound technique requires removal of insulation and reasonable pipe temperature for the contact ultrasonic transducers. A need exists to test a large range of inservice pipe component diameters without insulation removal. A new near real time cassette radiographic imaging system is under development to test pipe components through insulation while in service. The cassette system detector is optimized for use with an Ir-192 gamma ray source. It is a scintillator based, solid state line array with excellent photon capture efficiency due to the thickness of the dense scintillator material. The solid state detector array assembly is small, lightweight and rugged but able to respond effectively to the high energy, low intensity gamma rays after attenuation through large diameter pipe components. The array is mounted in a cassette frame with a linear motion within the frame boundary. It images an area defined by the width of the detector array and the length of the motion. The array measures radiographic intensities as it moves and outputs the data to a computer for storage and processing. The processed data provide pipe wall measurements and a radiographic image display. The technique responds to both internal and external corrosion and erosion as well as to internal features in the component.