Nondestructive Testing Procedures Research Articles

Adaptive use of prior information in inverse problems: an application to neutron depth profiling

A flexible class of Bayesian models is proposed to solve linear inverse problems. The models generalize linear regularization methods such as Tikhonov regularization and are motivated by the ideas of the image restoration model of Johnson et al (1991 IEEE Trans. Pattern Anal. Machine Intell. 13 413-25). The models allow for the existence of sharp boundaries between regions of different intensities in the signal, as well as the incorporation of prior information on the locations of the boundaries. The use of the prior boundary information is adaptive to the data. The models are applied to data collected to study a multilayer diamond-like carbon film sample using a nondestructive testing procedure known as neutron depth profiling.

Impact of FWD Testing Variability on Pavement Evaluations

Airfield pavement evaluations commonly include nondestructive testing. These evaluations are used for projecting pavement performance and for designing pavement rehabilitation options. To apply reliability concepts to these prediction and design scenarios, it is necessary to learn more about the variabilities associated with nondestructive testing and pavement evaluation procedures. In this study, twelve sites around the southeastern United States were tested with both a falling weight deflectometer and a heavy-weight deflectometer. The data were evaluated using the military procedure. The test data and the pavement evaluation results were examined for spatial variability and for test device variability. Two primary conclusions resulted from this study. The first primary conclusion is that the current military evaluation procedure does not provide a consistent level of reliability for evaluation results. The second primary conclusion is that the magnitude of the load used for deflectometer testing affects the evaluation results.

A STUDY OF ULTRASONIC WAVE PROPAGATION THROUGH PARALLEL ARRAYS OF IMMERSED TUBES

Tubular array structures are a very common component in industrial heat exchanging plant and the non-destructive testing of these arrays is essential. Acoustic methods using microphones or ultrasound are attractive but require a thorough understanding of the acoustic properties of tube arrays. This paper details the development and testing of a small-scale physical model of a tube array to verify the predictions of a theoretical model for acoustic propagation through tube arrays developed by Heckl, Mulholland, and Huang [1–5] as a basis for the consideration of small-scale physical models in the development of non-destructive testing procedures for tube arrays. Their model predicts transmission spectra for plane waves incident on an array of tubes arranged in straight rows. Relative transmission is frequency dependent with bands of high and low attenuation caused by resonances within individual tubes and between tubes in the array. As the number of rows in the array increases the relative transmission spectrum becomes more complex, with increasingly well-defined bands of high and low attenuation. Diffraction of acoustic waves with wavelengths less than the tube spacing is predicted and appears as step reductions in the transmission spectrum at frequencies corresponding to integer multiples of the tube spacing. Experiments with the physical model confirm the principle features of the theoretical treatment.

Effects of water absorption and osmotic degradation on long‐term behavior of glass fiber reinforced polyester

AbstractGlass fiber reinforced polyester composites, with gelcoat, are widely used as structural materials for hulls, pools, pipes, and tanks in aggressive environments, despite the lack of knowledge concerning their resistance to water in the long term. In addition, these materials may be damaged through an osmotic process, especially when immersed in water, as are boat hulls, and this phenomenon can lead to a delamination of the gelcoat and of the laminate plies. The aim of this experimental study is to evaluate the mechanical characteristics with time of orthotropic laminates subjected to accelerated tests of humid aging. The evolution of the properties with water absorption is followed by a nondestructive test procedure based on vibrational mode analysis. The results are additionally confirmed by quasi‐static bending and shear tests. It is shown that the main effects of water on the composite mechanical properties are the plasticization of the matrix an the osmotic delamination of the plies; on the other hand, gelcoat blistering had no influence on the durability. This paper highlights the need for and the complementarity of both nondestructive and destructive mechanical tests for studying the long‐term behavior of composites in marine environments.

Impact of Weight Falling onto the Ground

The application of some nondestructive testing procedures for soils and pavements, such as the spectral analysis of surface waves method, requires the use of dynamic sources at some point on the surface of the ground to create vibrations that can be recorded and related to the material characteristics of the medium. These sources are typically accomplished by means of falling weights of various sizes. This paper applies a simple mass‐spring‐dashpot model to assess the characteristics of the forces transmitted to the ground by the falling weight so as to be able to rationally decide on its size, mass, and dropping height. It is found that if inelastic effects are disregarded, a falling weight always rebounds; that the drop height affects only the impact velocity and amplitude of the contact force—not the duration of contact; and that increases in the drop weight lead to reductions in damping, increases in contact time, increases in contact force, and enhancement of the low‐frequency components in the Fourier spectrum of the contact force.

A knowledge-based system for nondestructive testing of polymeric composite components

This paper presents a formalization of the knowledge domain of nondestructive quality control of polymeric composite components. The formalization scheme presented in this paper has been implemented in a prototype knowledge-based expert system (KBES), called NICC for nondestructive inspection of composite components, to help in the quality assurance of these parts. Geometric and bonding characteristics of individual and assembled components are taken into account, as opposed to the better understood evaluation of well-behaved test specimens. The use of nondestructive techniques in the inspection of plastic and polymeric composites is fairly recent and hence, the knowledge required to develop a KBES is still very scattered and not yet fully covered in the literature. This study demonstrates both the feasibility of compiling and representing this knowledge domain and the possibility of translating it into an efficient automated tool capable of giving reliable expert-like advice at low cost. The reasoning process is divided into three stages. In the first stage, a polymetric composite component is completely defined according to features that are relevant for nondestructive inspection. In the second stage, all the discontinuities that may be present in the component are determined. Finally, in the third stage, appropriate nondestructive testing procedures are identified to detect each of the possible discontinuities.

A Knowledge-Based System for Nondestructive Testing of Polymeric Composite Components

Abstract This paper presents a formalization of the knowledge domain of nondestructive quality control of polymeric composite components. The formalization scheme presented in this paper has been implemented in a prototype knowledge-based expert system (KBES), called NICC for nondestructive inspection of composite components, to help in the quality assurance of these parts. Geometric and bonding characteristics of individual and assembled components are taken into account, as opposed to the better understood evaluation of well-behaved test specimens. The use of nondestructive techniques in the inspection of plastic and polymeric composites is fairly recent and hence, the knowledge required to develop a KBES is still very scattered and not yet fully covered in the literature. This study demonstrates both the feasibility of compiling and representing this knowledge domain and the possibility of translating it into an efficient automated tool capable of giving reliable expert-like advice at low cost. The reasoning process is divided into three stages. In the first stage, a polymetric composite component is completely defined according to features that are relevant for nondestructive inspection. In the second stage, all the discontinuities that may be present in the component are determined. Finally, in the third stage, appropriate nondestructive testing procedures are identified to detect each of the possible discontinuities.

A Knowledge-Based System for Nondestructive Testing of Polymeric Composite Components

Abstract This paper presents a formalization of the knowledge domain of nondestructive quality control of polymeric composite components. The formalization scheme presented in this paper has been implemented in a prototype knowledge-based expert system (KBES), called NICC for nondestructive inspection of composite components, to help in the quality assurance of these parts. Geometric and bonding characteristics of individual and assembled components are taken into account, as opposed to the better understood evaluation of well-behaved test specimens. The use of nondestructive techniques in the inspection of plastic and polymeric composites is fairly recent and hence, the knowledge required to develop a KBES is still very scattered and not yet fully covered in the literature. This study demonstrates both the feasibility of compiling and representing this knowledge domain and the possibility of translating it into an efficient automated tool capable of giving reliable expert-like advice at low cost. The reasoning process is divided into three stages. In the first stage, a polymetric composite component is completely defined according to features that are relevant for nondestructive inspection. In the second stage, all the discontinuities that may be present in the component are determined. Finally, in the third stage, appropriate nondestructive testing procedures are identified to detect each of the possible discontinuities.

Parameter design and expert systems in NDT : British Journal of Non-Destructive Testing, Vol. 33, No. 3, pp. 115– 120 (Mar. 1991)

In Non-Destructive Testing (NDT) of welds, the quality of inspection results of a welded structure is closely linked to the parameters used in the test procedure adopted. The formulation of the optimum test parameters depends on the knowledge and experience of the NDT specialist and requires inputs of several different types of expert knowledge. This paper will describe how parameter design can be used to increase the efficiency of NDT procedures by providing robust inspection parameters to a knowledge-based expert system as an ongoing research program to enhance industrial quality

Taguchi methods and expert systems in fabrication design

Quality improvement is a key objective in meeting reduced costs and increased productivity. It has therefore become an integral part of many organisations' business strategy. In the Non-Destructive Testing (NDT) of welds, the quality of inspection results from a welded structure is closely linked to the parameters used in the test procedure adopted. The formulation of the optimum test parameters depends on the knowledge and experience of the NDT specialist and requires inputs of several different types of expert knowledge. This experience which the human experts have is usually heuristic, judgemental, subjective or intuitive in nature. Moreover, the optimum procedures usually differ from one job to another. Hence, the application of the design of experimental techniques, such as Taguchi's approach, can be used to identify optimum conditions which are robust against unwanted disturbances in the testing environment while providing an improved degree of sensitivity. Taguchi methods (Taguchi, System of Experimental Design, Unipub Krauss, 1987; Phillip, Taguchi Techniques for Quality Engineering, McGraw-Hill, 1988) which are aimed at reducing variability and cost, can be used to improve the sensitivity of ultrasonic measurement methods through the use of the Signal-to-Noise (SN) ratio as the quality characteristic of a measuring system. Traditionally, the quality of measuring systems has been evaluated on the basis of repeatability. Another important element associated with the quality of measurement systems is ‘sensitivity’, which is the ability to perceive and discriminate between two signals or samples to be measured. Parameter design in Taguchi methodology can be used to provide the human experts with a means of optimising inspection parameters. Therefore, knowledge-based systems incorporating heuristic algorithms, as well as analytical and empirical models provided by Taguchi methods can in turn provide human experts with support to further improve their decision making. This paper will describe how parameter design can be used to increase the efficiency of NDT procedures by providing robust inspection parameters for a knowledge-based expert system, an ongoing research program to enhance industrial quality.

Knowledge-based approach to the formulation of ultrasonic non-destructive testing procedures : IEE Proceedings, Vol. 136, Pt. A, No. 3, pp. 134–140 (May 1989)

Knowledge-based approach to the formulation of ultrasonic non-destructive testing procedures : IEE Proceedings, Vol. 136, Pt. A, No. 3, pp. 134–140 (May 1989)

Mathematical Modeling and NDT: A State of the Art

Abstract During the past decade or so there have been significant advances in the mathematical modeling of nondestructive testing (NDT) techniques. The current state of modeling is reviewed, with the aim of demonstrating the important role that it can play in improving and validating NDT techniques and procedures. This paper was presented at the 6th International Offshore Mechanics and Arctic Engineering Symposium, (1987). Since that time, a number of advances have been made in mathematical modeling. A more recent review of mathematical modeling techniques, with additional references, is currently in preparation by the authors.

Knowledge-based approach to the formulation of ultrasonic nondestructive testing procedures

In nondestructive testing there is considerable potential for the application of knowledge-based systems. This ranges from the selection of suitable testing techniques, through the formulation of test procedures, to the analysis and interpretation of test results. In this particular case, an expert system shell was used to develop a system which assists in the derivation of procedures for the ultrasonic inspection of welds in ferritic steel. The components of the system are described and examples given of its use and subsequent outputs. The advantages of such an approach are improvements in the speed and accuracy of procedure writing, especially for less experienced personnel, the potential as a training aid and the ability to document the system consultation.

A review of work related to defining the reliability of non-destructive testing

This paper reviews work done in recent years in many countries aimed at helping to define the reliability and effectiveness of non-destructive testing procedures in detecting, reporting and sentencing crack-like flaws. Much of the work discussed relates to ultrasonic testing and refers to thick welded low alloy steel weldments, austenitic steel plates and pipes and to mixed-metal welds. The study involves literature surveys and replies to a questionnaire letter. The results in general support the conclusions of CEC/DECD Programme for the Inspection of Steel Components (PISC II) and indicate the important areas for further work, for example that to be done in PISC III.

PISC exercises: Looking for effective and reliable inspection procedures

Since 1974 in Europe and since 1969 in USA, exercies have been organized in order to verify the effectiveness of NDT (non-destructive testing), which contribute to the reliability assessment of pressurized steel components. Exercises such as PISC consider NDT procedures of the ISI type (in-service inspection) to be tested on samples which represent structures of reactor pressure vessels (RPV). These test plates contain defects artificially introduced. In the near future, samples will be reactor structure pieces containing real service induced defects. These exercises as well as those organized in USA (PVRC), Japan (JPVRC) and UK (DDT) have to be considered as steps of the evolution of NDT: • - effectiveness verification (PISC-1: 1974–1979); • - identification of performance techniques (PISC-II: 1981–1984); • - validation of results on real structures (PISC-III: 1985-□).

On In-Place Strength of Concrete and Pullout Tests

Abstract The current status of in-place strength evaluation of concrete is discussed. A literature survey regarding the controversy surrounding the assessment of concrete strength through field-cast laboratory-cured cylinder tests is presented. Inconsistencies associated with the drilling and testing of cores for determining in-place concrete strength are pointed out. On the basis of these arguments, the necessity of developing alternative nondestructive test procedures is emphasized. This is followed by a detailed discussion on the status of the pullout test method as a measure of compressive strength of in-place concrete, which appears to be a potentially feasible nondestructive test procedure. The present paper constitutes a state of the art report on the aforementioned topics and contains appropriate recommendations from the authors.

Quantitative ultrasonics

Ultrasonic non-destructive testing, as currently used in industry, is limited by its non-quantitative capabilities. In this sense, non-quantitative means that current technology is capable only of producing a signal that indicates the presence of a flaw, but it is unable to say anything about the characteristics of the flaw, e.g. its size, shape, orientation, and the m aterial of which it is composed (void or inclusion). This lim itation has been brought into sharp focus in recent years with the advent of fracture mechanics as a m ajor structural design and m aintenance philosophy. Since fracture mechanics is quantitative in nature, its effective utilization as an accept/reject criterion for flaws in materials and structures thus requires that quantitative inform ation be available from the non-destructive test procedures used to assure the design. W ith this lim itation in mind, the Defense Advanced Research Projects Agency (Darpa) and the Air Force M aterials Laboratory (A.F.M .L.) jointly initiated work at the Science Center, Rockwell International, to explore and to improve this situation. The work is structured to include both Science Center and university participants, and includes research and development in several areas necessary to achieve a quantitative capability. These areas include transducers, acoustic imaging, and defect characterization. In this paper principal emphasis is placed upon the defect characterization work that has been done. The approach that has been used is that of ultrasonic scattering, an approach which recognizes that several measurements must be taken at different angles and frequencies in order to acquire sufficient information to characterize a flaw. Items that are discussed include the design and preparation of a set of flawed samples in which the flaws are well characterized, theoretical developments that describe the ultrasonic scattering interaction with these flaws, experimental verification of these models, and inversion processes that have been developed to process the data and deduce flaw parameters from the ultrasonic measurements. A comparison of the deduced flaw param eters with the initially known values is given. Two other topics are discussed. One of these concerns recent developments in the analysis of long wavelength scattering which suggest that it should be possible to obtain stress intensity factors from ultrasonic measurements. The second item is concerned with recent developments in non-contact transducers (electromagnetic acoustic transducers (e.m.a.ts)) that are particularly related to weld inspection.

The Electromagnetic Basis for Nondestructive Testing of Cylindrical Conductors

Using an idealized model, we deduce the impedance per unit length of long solenoid of many turns that contains a cylindrical sample. The sample with a specified conductivity and magnetic permeability need not be centrally located within the solenoid provided all transverse dimensions are small compared with the free-space wavelength. The derivation is relatively straightforward and it provides a justification for earlier use of the impedance formula. The dual problem , where the solenoid is replaced by a toroidal coil is also considered. It is shown that both excitation methods have merit in nondestructive testing procedures.

Determination of column-buckling criteria using vibratory data

A mathematical model is presented which describes a nondestructive testing procedure for determining buckling criteria for structures. The procedure requires identification of the structure's support boundary conditions using vibration data. Column-buckling experiments are presented which validate the model. The results illustrate the feasibility of using such models to predict the buckling load for structures whose support boundary conditions are not known in advance of service.

Interrelation of structural stability, stiffness, residual stress and natural frequency

Results have been collected on studies relating the stability load of a structure to stiffness and natural frequency. Additional experimentation has been done to include effects of residual stresses and the major portion of this paper is devoted to a discussion of these studies. Finally, further examinations have been made of recent theories to relate stability load, stiffness, frequency and residual stress. The results have been reported here in order to reveal the range of relationships that can be found among these four structural features, and to demonstrate a reasonably sound basis for non-destructive testing procedures to determine residual stresses and structural stability. Hopefully, it also will stimulate further research in this hitherto neglected area.