Nondestructive Evaluation Procedure Research Articles

Ultrasonic evaluation of ply and interleaf layer properties of interleaved composite laminates

An ultrasonic nondestructive evaluation procedure is presented for the ply and interleaf layer properties of carbon/epoxy composite laminates having interleaf resin layers at their interlaminar interfaces. It is shown that the material properties of plies (density, thickness, and transversely isotropic complex elastic moduli) and elastic interleaf layers (density, thickness, Young’s modulus, and Poisson’s ratio) can be identified by best fitting the theoretical energy transmission spectra of longitudinal waves through the laminate immersed in water to those obtained in ultrasonic measurement. It is also demonstrated that compared to the mass-less and null-thickness spring-type interlaminar interface model employed in the previous works, the present finite-thickness interleaf layer model can better reproduce the experimental transmission spectra of a unidirectional interleaved composite laminate containing ultrasonic bandgaps. Furthermore, the property characterization in the case where the plies and interleaf layers are assumed to be elastic and viscoelastic, respectively, is also examined. It is also shown that the ply and interleaf layer properties determined for the unidirectional laminate can be used to reproduce the transmission spectra measured for a quasi-isotropic laminate consisting of the same plies and interleaf layers.

Towards a remote inspection of jet engine blades using time reversal

Assessing the state of damage of jet engine blades is a burning issue in aeronautics. However, most nondestructive evaluation procedures require cumbersome installations and removal of the blades from the engines, which is time and money consuming. We present a non-intrusive acoustic monitoring technique that could be applied for fast remote inspection of selected blades inside a jet engine. The technique uses a time reversal mirror in the audible frequency range to selectively excite a targeted blade a few meters away. The resonance frequencies of the blade are measured at the location of the excitation using a laser vibrometer. The technique is first applied on a few individual blades and then inside a jet engine. Selective excitation of a difficult-to-access blade among others inside a cavity is shown. In laboratory, some damage (material removal or slit) is created on a set of initially intact blades, which cause a shift in their resonance frequencies. By evaluating these frequency shifts, we are able to remotely detect millimeter size damage on the blades. Finally, the on-site applicability and the uncertainties of the method are discussed.

Failure analysis of aircraft main landing gear cylinder support

The main concern in aircraft structures is flight safety. One of the constraints to consider when designing safe aircraft parts is weight. The design of the landing gear structures is difficult because it must ensure flight safety without adding excessive weight.During takeoff, the main landing gear of a cargo plane did not retract. The landing procedure went off without a hitch. The maintenance crew disassembled and inspected the main landing gear to determine the source of the problem. The main landing gear cylinder support was discovered to be in broken condition. The part was broken at the 90-degree corner region. The location of the fracture is subjected to high stresses in service conditions especially during braking with a heavily loaded aircraft.Detailed destructive and, non-destructive evaluation procedures were applied to reveal the root cause or causes of the failure. The determination of the root cause is crucial to prevent a similar failure in the future.Visual inspection, electrical conductivity test, fractography, microstructural evaluation, chemical analysis, hardness test were applied to the part. After examination, it was determined that the support had failed due to fatigue. The conditions of use, low radius geometry in the crack origin, rough machined surface, and pitting corrosion all played a role in the failure.

Automatic Identification Algorithm of Equivalent Electrochemical Circuit Based on Electroscopic Impedance Data for a Lead Acid Battery

Obtaining tools to analyze and predict the performance of batteries is a non-trivial challenge because it involves non-destructive evaluation procedures. At the research level, the development of sensors to allow cell-level monitoring is an innovative path, and electrochemical impedance spectrometry (EIS) has been identified as one of the most promising tools, as is the generation of advanced multivariable models that integrate environmental and internal-battery information. In this article, we describe an algorithm that automatically identifies a battery-equivalent electrochemical model based on electroscopic impedance data. This algorithm allows in operando monitoring of variations in the equivalent circuit parameters that will be used to further estimate variations in the state of health (SoH) and state of charge (SoC) of the battery based on a correlation with experimental aging data corresponding to states of failure or degradation. In the current work, the authors propose a two-step parameter identification algorithm. The first consists of a rough differential evolution algorithm-based identification. The second is based on the Nelder–Mead Simplex search method, which gives a fine parameter estimation. These algorithm results were compared with those of the commercially available Z-view, an equivalent circuit tool estimation that requires expert human input.

Assessing internal soundness of hardwood logs through acoustic impact test and waveform analysis

The objective of this study was to explore the potential of an acoustic impact test as a nondestructive evaluation procedure to assess the soundness of hardwood logs in terms of internal decay, void, and defect ratio. Fifteen logs of four hardwood species (black cherry, white oak, red oak, and cottonwood) were obtained and subjected to acoustic impact testing. The logs were subsequently dissected for visual examination and physical mapping of the internal defects. The acoustic response signals were analyzed to derive acoustic velocity (through FFT), time centroid (through moment analysis), and the first- and second-order damping ratio (through continuous wavelet transform). The longitudinal acoustic velocity was found to have a negative, nonlinear relationship with defect ratio (R2 = 0.72), but it lacked sensitivity to small defects and was affected by species. Time centroid proved to be a better predictor than acoustic velocity with an improved correlation with log defect ratio (R2 = 0.87). Wavelet-based damping ratio was found to have a close linear relationship with log defect ratio. Comparing with the first-order damping ratio, the second-order damping ratio had a better predicting power (R2 = 0.92) and was not affected by type and location of defects. The results further indicated that a combination of acoustic velocity, time centroid, and the first- and second-order damping ratios could yield the optimal prediction of log defect ratio. However, considering the sensitivity and simplicity of the waveform analysis, the second-order damping ratio of the response signals could be the best single predicting parameter for assessing the internal soundness of hardwood logs.

Nondestructive Evaluation – A Critical Part of Structural Integrity

The structural integrity of modern structures and systems depend on the use and capabilities of nondestructive evaluation (NDE) for quality assurance in production; condition monitoring and repair assessments in service; risk analysis; and service/lifetime retirement. NDE is an ancient technology that has been applied, in many forms, since the beginning of time. The development and application of fracture mechanics was a revolution in design and structures management; imposed new and demanding requirements for NDE applications; and incorporated NDE as a critical part of design, production and management of critical structures and systems. New NDE requirements included quantification of capabilities and supporting considerations and technologies for development, validation, application and assessment of NDE capabilities and practices. NDE methods provide indirect measures / assessments of a desired property or condition and involve complex integration of parameters to produce the desired end result. Assessments of the capability and reliability of NDE procedures is continually evolving as an NDE engineering technology that is generally described in terms of a “probability of detection” (POD) metric. This paper summarizes the origin of the POD metric; various approaches to addressing POD requirements; considerations in NDE engineering; and suggested paths forward.

Dynamic Survey of the Musmeci Bridge by Joint Application of Ground-Based Microwave Radar Interferometry and Ambient Noise Standard Spectral Ratio Techniques

This letter aims at analyzing the potentialities of the ground-based microwave radar interferometry technique for the dynamic characterization of civil infrastructures. This technique has been applied to estimate the fundamental dynamic parameters of the reinforced concrete Musmeci bridge in Basilicata region (southern Italy). The results have been validated by the comparison with the ones obtained applying consolidated techniques using data from accelerometers and tromometers. The good agreement obtained could suggest the joint application of such techniques as a new technological approach to set up a non-invasive and non-destructive evaluation procedure for structural health monitoring of infrastructures.

Modelling and measurement of the nonlinear behaviour of kissing bonds in adhesive joints

The non-destructive evaluation of adhesively bonded joints is a subject of significant industrial and academic interest. It is thought that areas of interfacial weakness develop firstly into kissing bonds before finally disbonding. Critically, there is a requirement to detect such defects at the earliest possible stage. Whilst a number of techniques such as high frequency ultrasonic C-scanning are able to robustly detect disbonding, the detection of interfacial weakness has proved elusive. In this paper we focus our attention on the kissing bond state, which we consider to be a bond still in intimate contact, but with zero, or minimal, strength. Various researchers have shown that kissing bonds of this type behave nonlinearly when illuminated with ultrasound and have sought to make this the basis of a non-destructive evaluation procedure. In this paper we use a one-dimensional time domain model that includes an interfacial nonlinearity to predict the interaction of ultrasonic pulses with a kissing bond. With this model we show that the measured nonlinearity is highly dependent on the thickness of the adhesive layer to wavelength ratio. These effects are explained by the observation that the linear dynamics of the multi-layer bonded system act as a series of bandpass filters on the nonlinear signals generated at the kissing interface. It is suggested that, in order to make robust nonlinear measurements, these filtering characteristics should be known and compensated for.

FE model updating of welded structures for identification of defects

A non-destructive evaluation procedure for identifying defects using finite element (FE) model updating based on natural frequencies is presented in this paper. Welded structures that are intended to represent a common configuration used in automotive body construction are investigated. The first procedure is to find the measured natural frequencies of both benchmark and defective structures, by carrying out the experimental modal analysis (EMA). Then, the FE model of the benchmark structure is developed and updated by modifying some design parameters from their initial values. FE modelling is accomplished with MSC NASTRAN and the FE model updating procedure is performed using the NASTRAN optimisation code (SOL200). Next, appropriate defects on the defective structure are observed by performing a visual inspection. Information from the visual inspection and the updated benchmark model is incorporated when modelling the defective structure, followed by the FE model updating procedure to identify the defect parameters.

Autonomous corrosion detection in gas pipelines: a hybrid-fuzzy classifier approach using ultrasonic nondestructive evaluation protocols

In this paper, a customized classifier is presented for the industry-practiced nondestructive evaluation (NDE) protocols using a hybrid-fuzzy inference system (FIS) to classify the corrosion and distinguish it from the geometric defects or normal/healthy state of the steel pipes used in the gas/petroleum industry. The presented system is hybrid in the sense that it utilizes both soft computing through fuzzy set theory, as well as conventional parametric modeling through H(infinity) optimization methods. Due to significant uncertainty in the power spectral density of the noise in ultrasonic NDE procedures, the use of optimal H(2) estimators for defect characterization is not so accurate. A more appropriate criterion is the H(infinity) norm of the estimation error spectrum which is based on minimization of the magnitude of this spectrum and hence produces more robust estimates. A hybrid feature set is developed in this work that corresponds to a) geometric features extracted directly from the raw ultrasonic A-scan data (which are the ultrasonic echo pulses in 1-Dtraveling inside the metal perpendicular to its 2 surfaces) and b) mapped features from the impulse response of the estimated model of the defect waveform under study. An experimental strategy is first outlined, through which the necessary data are collected as A-scans. Then, using the H(infinity) estimation approach, a parametric transfer function is obtained for each pulse. In this respect, each A-scan is treated as output from a defining function when a pure/healthy metal's A-scan is used as its input. Three defining states are considered in the paper; healthy, corroded, and defective, where the defective class represents metal with artificial or other defects. The necessary features are then calculated and are then supplied to the fuzzy inference system as input to be used in the classification. The resulting system has shown excellent corrosion classification with very low misclassification and false alarm rates.

Damage Assessment of a Cracked Bar: Effect of Material Nonlinearity on Vibro-Impact Response

Structural health monitoring is receiving much attention as a means to prevent catastrophic failure in structures in operating conditions. In most cases fracture is caused by the growth of crack, which cannot be precluded in many engineering structures. Moreover, to have an accurate quantitative estimate of crack tolerance of a structure to prevent fracture of load bearing components, an effective non-destructive evaluation procedure becomes necessary to monitor the structure under working conditions.

Defect identification under uncertain blast loading

A novel finite element-based system identification procedure is proposed to detect defects in existing frame structures when excited by blast loadings. The procedure is a linear time-domain system identification technique where the structure is represented by finite elements and the input excitation is not required to identify the structure. It identifies stiffness parameter (EI/L) of all the elements and tracks the changes in them to locate the defect spots. The similar procedure can also be used to monitor health of structures just after natural events like strong earthquakes and high winds. With the help of several numerical examples, it is shown that the algorithm can identify defect-free and defective structures even in the presence of noise in the output response information. The accuracy of the method is much better than other methods currently available even when input excitation information was used for identification purpose. The method not only detects defective elements but also locate the defect spot more accurately within the defective element. The structures can be excited by single or multiple blast loadings and the defect can be relatively small and large. With the help of several examples, it is established that the proposed method can be used as a nondestructive defect evaluation procedure for the health assessment of existing structures.

Material characterization of composite laminates using dynamic response and real parameter-coded microgenetic algorithm

An efficient nondestructive evaluation procedure is proposed for inversely determining material constants of composite laminates using dynamic response at one point on the plate surface. Material constants of composite laminates are determined by minimizing the difference between the measured dynamic response of the actual plate and the computed response of the plate with assumed material properties. For robust and efficient function minimization, a real parameter-coded microgenetic algorithm (real-μGA) is proposed on the basis of the existing binary coded uniform microgenetic algorithm (uniform μGA). Four different crossover operators are constructed for the real-μGA. Performances of the present real-μGA and the existing uniform μGA are studied using several typical benchmark test functions and an order-3 deceptive function. The present real-μGA is then implemented as the inverse solver in the minimization process of material characterization. From hundreds of tests conducted on the benchmark functions, the order-3 deceptive function, and the material characterization problems, it is found that the real-μGA is two to five times faster in converging to the global optimum compared with the uniform μGA. Numerical examples for material characterization of composite laminates have demonstrated the robustness, efficiency, and accuracy of the proposed procedure.

Time-Domain Reflectometry to Detect Voids in Posttensioning Ducts

Because incompletely grouted posttensioned ducts result in voids, the steel strands are vulnerable to premature corrosion. This paper describes a nondestructive evaluation (NDE) procedure that allows bridge owners to ensure that posttensioned ducts are properly grouted (i.e., have no voids). The NDE procedure uses time-domain reflectometry (TDR), a technique developed by electrical engineers for locating discontinuities in transmission lines. TDR involves sending a signal created by a step-pulse generator through a transmission line, determining whether the signal is reflected back, and, if it is reflected back, using the elapsed time to determine the location of the discontinuity. Prior research funded by the Delaware Department of Transportation and the National Science Foundation has shown that TDR can be used to detect corrosion on strands and can be implemented in the field. To detect and evaluate voids, the transmission line is placed either in or adjacent to the region where a void is suspected. Th...

Non-destructive evaluation of ceramic candle filters using artificial neural networks

Ceramic candle filters play an important role in coal-based turbine system for a modern power plant. However, after exposure to the high pressure and high temperature in the gas turbine chamber, the effectiveness of the filters deteriorates over time. Their failure to perform may create catastrophic consequences for the multi-million dollar equipment downstream. A non-destructive evaluation procedure using artificial neural networks is proposed to examine the filters. In lieu of experimental data, the vibration signatures of filters damaged to various degrees are created by means of analytical simulation. Then, a feed-forward artificial neural network and a radial basis function neural network are built and trained to evaluate the signatures for the purpose of determining the filters’ degree of deterioration. Good results are obtained and presented here. The application of the proposed procedure should not be confined to the ceramic candle filters alone. It is a general procedure that will find many applications on the evaluation of other structural components and engineering products in the industry.

Nondestructive Evaluation of Tuned-Mass-Damper-Type Vibration Absorbers Using Vibration Signatures

Nondestructive evaluation methods are often essential in order to objectively assess the condition of structural and ancillary systems for bridges, particularly in cases where visual methods provide only limited or subjective data and the function of the systems being evaluated may not be disturbed using destructive evaluation techniques. This paper describes a nondestructive evaluation procedure that was developed to objectively assess the current condition of a system of 920 aged vibration absorbers installed on a long span cantilever truss bridge. The vibration absorbers, which are essentially tuned mass dampers consisting of a steel weight attached to the end of a viscoelastic rubber stem, were installed soon after the bridge was opened to mitigate the effects of excessive wind-induced vibrations that had occurred in many of the truss members. A nondestructive evaluation procedure was developed because the vibration absorbers had to remain in service during the evaluation process, and there were only a limited number of spare absorbers that could be used to replace any that might be destructively tested. The complete evaluation program included nondestructive vibration testing in the laboratory using impact methods to determine the current dynamic properties of the absorbers, and field testing to evaluate the energy dissipation characteristics of the installed vibration absorbers as they were actually operating. In addition, a limited number of destructive material tests were conducted in order to corroborate the results of the nondestructive tests. This evaluation program revealed that the current performance characteristics of the aged vibration absorbers were within the limits of the original design specifications, and that the synthetic rubber material used for the vibration absorbers had experienced no appreciable deterioration after nearly 25 years of continuous service.

Inspection processes must compliment systems inspected

If the goal is to improve either aviation or shuttle safety and systems reliability, then modern methods of wire systems diagnostics, prognostics, mediation, repair, and validation are a must. This requires using modern non-destructive evaluation (NDE) procedures and equipment which yields information that supports the operator's wire health management program and feeds into his aging aircraft or shuttle containment processes. Commonly used wire inspection processes do not compliment aircraft electrical systems making it difficult to diagnose wiring problems or manage wiring systems health. The wire inspection tools in common use today can be represented by the volt/ohm meter, the meg/ohm meter, and visual techniques. The two meters only measure conductivity, connectivity, and insulation breakdown strength. Visual techniques, mirror and flashlight methods only reach about 25% of the aircraft wiring and subjectively identify only physical faults of the insulation and simple damaged components. Little can be determined relative to the wire, insulation, bundle, connector, connector pins, backshell, wire supports, grounding, shielding, or intended electrical systems performance. All items where data is necessary to analyze and manage the health of the system. Guidance material is currently not available for the electrical repairman for even a simplified zonal inspection. The user community also reports gross shortcomings in the guidance supplied by the manufacture's maintenance and repair manuals.

Science and technology of non-destructive testing, evaluation and characterisation

The quality of life available to the majority of citizens of any country is a direct measure of its state of economy. India has shown the quality consciousness through its rich tradition, heritage, monuments and idols. From the heritage to the atomic, space and information age, India has matured as a nation endowed with expertise in relevant and critical technologies. In India there has been a sustained and comprehensive approach to the development of industries for production of precision, strategic and heavy components of high quality through the application of non-destructive evaluation (NDE) techniques and procedures. A large number of non-destructive testing techniques have been developed in India by strategic and core sectors for in-house requirements. Academic institutes have played a key role in nurturing excellence in the area. The knowledge base is made available to the needy industries. With the availability of these techniques, together with the advent of advanced electronics, innovations in sensor technology, availability of computers and signal and image processing methodologies, improvement in detection sensitivity and quantitative characterisation of defects and assessment of microstructural degradation have taken place. The outcome of these developments is the improvement in fitness for purpose of fabricated components and their performance in service with a possibility for their life extension. An example is the front line research carried out and the expertise developed at IGCAR in the area of NDT&E in the last two decades. The expertise has been effectively utilised for finding reliable, comprehensive and cost-effective solutions for many unique and challenging problems in strategic (nuclear, space, and defence) and core (power, chemical and petrochemical) sectors. In this paper an overview of the authors' experience in the developments and applications of advanced NDE methodologies for a variety of applications has been given.

Virtual Inspection: Optimum Sample Size for POD Experiment

Engineers responsible for life prediction and inspection of aerospace components are often tasked with demonstrating the capability of an inspection. It is extremely important to establish that the quality of the particular nondestructive inspection procedure is good enough to satisfy the safety requirements specified by the Federal Aviation Administration and/or the Military Organizations. The established and accepted metric for characterizing the capability of a nondestructive evaluation procedure is the probability of detection (POD) as a function of the crack size. Typically, such a demonstration requires the fabrication of a number of specimens with controlled, quantified defects or cracks. Engineers planning a demonstration need to know how many specimens they should include in the test plan. Determining the number of test specimens to be produced has been more guesswork than science. Producing arbitrarily a large number of defect specimens is not a good option because producing such defect specimens is a very costly activity in most cases. On the other hand, if too few defect specimens are produced in an unplanned way the assessment of the POD function will not be good. Therefore, it is important to use a sample of appropriate minimum size that still achieves the quantitative requirement for demonstrating the capability of a nondestructive inspection scheme. In this article, we will develop a simulation-based algorithm that will help users of the nondestructive evaluation procedures to choose an optimal sample size and a test plan such that the “standard” requirement is satisfied.

Experimental dynamic characterization of an FRP composite bridge superstructure assembly

A system comprised of concrete filled, filament wound, circular carbon/epoxy girders and an E-glass/polyester deck, representative of a bridge section in the positive moment region was tested at large scale to assess the overall and component structural response. The system was characterized for stiffness and overall response under monotonic and cyclic fatigue loads. Forced vibration testing was conducted as part of a level I non-destructive evaluation (NDE) procedure at each of the test stages, including after failure. Experimental results from the tests were seen to correspond well with analytical results for mode shapes and frequencies obtained through an eigenvalue analysis of a plane-grillage finite element model. The test method was shown to be effective in indicating changes in response as a function of load level and damage accumulation, and is expected to have significant potential for eventual routine health monitoring and damage detection of such structural systems in the field.