Nondestructive Testing Of Materials Research Articles

Measurement-Based Thermal Modeling Using Laser Thermography

There have been several studies in using infrared thermography for nondestructive evaluation and testing of materials. Some studies have explored the potential of using thermography for classification of materials based on their thermal response. However, the modeling behind these efforts is rather simplistic, and in some ways not corresponding well with practical applications. This paper presents a realistic model-based approach for characterizing unknown materials using laser thermography. The process being modeled is laser excitation step thermography with finite but not infinitesimal excitation length and uniform distribution over a finite radius. A mathematical model, based on the heat equation that governs the flow of heat in materials, is introduced to characterize objects based on their response to thermal excitation. Experimental results consistently demonstrated the ability of the proposed approach to classify different materials based on their thermal properties. This contactless characterization method might prove to be suitable for a range of applications including teleoperation, haptic mapping and multimodal human computer interaction.

Cultural Heritage Studies with Mobile NMR.

Nuclear magnetic resonance (NMR) provides in situ information about selected isotope densities in samples and objects, while also providing contrast through rotational and translational molecular dynamics. These parameters are probed not only in NMR spectroscopy and imaging but also in nondestructive materials testing by mobile stray-field NMR, the unique properties of which are valuable in cultural heritage studies. We present recent progress in the analysis of cultural heritage with mobile 1 H NMR stray-field sensors, for which the detection zone is outside of the NMR magnet. Prominent applications include the analysis of stratigraphies in paintings and frescoes, and the assessment of material states changing under the impact of aging, conservation, and restoration.

Comparing the Efficiency of Ultrasonic Infrared Thermography under High-Power and Resonant Stimulation of Impact Damage in a CFRP Composite

The quality control of composite materials remains an important topic of research in nondestructive testing (NDT) of modern materials, in particular, the ones intended for aerospace industry. Over the last decade, there has been a noticeable increase in interest to the ultrasonic stimulation of tested materials and analysis of dynamic temperature distributions. This method is commonly implemented with two techniques, viz. high-power stimulation at a fixed acoustic-signal frequency and low-power resonant ultrasonic stimulation. Results are provided on comparing the above ultrasonic NDT methods using the example of an impact damage in a graphite epoxy-filled composite. The comparison is made based on the criteria of temperature signals, revealed flawed zone, and productivity of testing.

Elastic wave dispersion and attenuation caused by multiple types of disc-shaped inclusions

PurposeThe purpose of this paper is to numerically investigate time-harmonic elastic wave propagation with the analysis of effective wave velocities and attenuation coefficients in a three-dimensional elastic composite consisting of infinite matrix and uniformly distributed soft, low-contrast and absolutely rigid disc-shaped micro-inclusions.Design/methodology/approachWithin the assumptions of longitudinal mode of a propagating wave as well as dilute concentration and parallel orientation of inclusions in an infinite elastic matrix, Foldy’s dispersion relation is applied for introducing a complex and frequency-dependent wavenumber of homogenized structure. Then, the effective wave velocities and attenuation coefficients are directly defined from the real and imaginary parts of wavenumber, respectively. Included there a far-field forward scattering amplitude by a single low-contrast inclusion given in an analytical form, while for the other types of single scatterers it is determined from the numerical solution of boundary integral equations relative to the displacement jumps across the surfaces of soft inclusion and the stress jumps across the surfaces of rigid inclusion.FindingsOn the frequency dependencies, characteristic extremes of the effective wave velocities and attenuation coefficients are revealed and analyzed for different combinations of the filling ratios of involved types of inclusions. Anisotropic dynamic behavior of composite is demonstrated by the consideration of wave propagation in perpendicular and tangential directions relatively to the plane of inclusions. Specific frequencies are revealed for the first case of wave propagation, at which inclusion rigidities do not affect the effective wave parameters.Originality/valueThis paper develops a micromechanical study that provides a deeper understanding of the effect of thin-walled inclusions of diversified rigidities on elastic wave propagation in a three-dimensional composite. Described wave dispersion and attenuation regularities are important for the non-destructive testing of composite materials by ultrasonics.

Investigating Small-Scale Air–Sea Exchange Processes via Thermography

The exchange of trace gases such as carbon dioxide or methane between the atmosphere and the ocean plays a key role for the climate system. However, the investigation of air-sea gas exchange rates lacks fast and accurate measurement techniques that can be used in field campaigns, e.g. onboard a ship on the ocean. A promising way to overcome this deficiency is to use heat as a proxy tracer for gas transfer. Heat transfer rates across the aqueous boundary layer of the air-water interface can be measured via thermography with unprecedented temporal and spatial resolution in the order of minutes and meters, respectively. Either passive or active measurement schemes can be applied. Passive approaches rely on temperature differences across the water surface that are caused naturally by radiative and evaporative cooling of the water surface. Active measurement schemes force an artificial heat flux through the aqueous boundary layer by means of heating a patch at the water surface with an appropriate heat source, such as a $\textrm{CO}_2$ laser. For the active measurement approach the choice of the excitation signal is crucial. It is beneficial to apply periodic heat flux densities with different excitation frequencies. In this way, the air-water interface can be probed for its response in terms of temperature amplitude and phase shift between excitation signal and temperature response. This concept from linear system theory is also well established in the field of non-destructive material testing, where it is known as lock-in thermography. This article gives a short introduction into air-sea gas exchange, before it presents an overview of different thermographic measurement techniques used in wind-wave facilities and at sea from their early implementations. The article closes with a novel multifrequency excitation scheme for even faster measurements.

Quantitative evaluation of active thermography using contrast-to-noise ratio.

Active thermography is an infrared-based technique for nondestructive testing of materials. It often uses advanced evaluation techniques based on temperature spatial and temporal changes. Results of active thermography are contrast differences, which indicate possible defects in an inspected material. These differences cannot be quantified by temperature. This contribution is focused on the active thermography results' evaluation parameters and the contrast-to-noise ratio method, which can be used for quantitative evaluation of the results. Different result interpretation procedures are introduced. The influence of a selection method for indication and reference regions and the effect of image scaling on inspection results are discussed.

Non-destructive testing of ceramic materials using mid-infrared ultrashort-pulse laser

The non-destructive testing (NDT) of ceramic materials using mid-infrared ultrashort-pulse laser is investigated in this study. The discrete ordinate method is applied to solve the transient radiative transfer equation in 2D semitransparent medium and the emerging radiative intensity on boundary serves as input for the inverse analysis. The sequential quadratic programming algorithm is employed as the inverse technique to optimize objective function, in which the gradient of objective function with respect to reconstruction parameters is calculated using the adjoint model. Two reticulated porous ceramics including partially stabilized zirconia and oxide-bonded silicon carbide are tested. The retrieval results show that the main characteristics of defects such as optical properties, geometric shapes and positions can be accurately reconstructed by the present model. The proposed technique is effective and robust in NDT of ceramics even with measurement errors.

Nondestructive Evaluation of Rubber Composites Using Terahertz Time Domain Spectroscopy

In recent years, with the progress of science, more and more detection methods are being used in various fields. However, the nondestructive testing of nonmetallic materials still needs further study. In this paper, an analysis of the time domain characteristics of rubber materials using terahertz detection technology was carried out, obtaining different defect rubber material spectral characteristics as well as imaging results and data. The results show that the THz spectrum imaging technique can detect the thickness of rubber material in the 0.1 ~ 4.0 terahertz band, and the image is clear and the resolution high. Meanwhile the time domain waveform obtained is sensitive to the debonding defects of the sample rubber, is suitable for judging the overall performance of the rubber inner defect detection, and can provide the scientific basis for rubber material performance.

Application of finite elements heterogeneous multi-scale method to eddy currents non destructive testing of carbon composites material

In this present paper, a simulation of eddy current non-destructive testing (EC NDT) on unidirectional carbon fiber reinforced polymer is performed; for this magneto-dynamic formulation in term of magnetic vector potential is solved using finite element heterogeneous multi-scale method (FE HMM). FE HMM has as goal to compute the homogenized solution without calculating the homogenized tensor explicitly, the solution is based only on the physical characteristic known in micro domain. This feature is well adapted to EC NDT to evaluate defect in carbon composite material in microscopic scale, where the defect detection is performed by coil impedance measurement; the measurement value is intimately linked to material characteristic in microscopic level. Based on this, our model can handle different defects such as: cracks, inclusion, internal electrical conductivity changes, heterogeneities, etc. The simulation results were compared with the solution obtained with homogenized material using mixture law, a good agreement was found.

Procena količine oslobođene toplote sagorevanja termovizijskom kamerom

Infrared thermography has for many years been used as a standard and reliable method for non-destructive testing of various materials. The paper presents additional applications of the method - for monitoring combustion of different materials and tracking undesirable ignition of certain liquids, gases and coals. It also includes a quantitative analysis of flame temperatures during combustion of samples of different materials.

Applications of laser ultrasonic technique on nondestructive testing and evaluation of materials

Nondestructive testing (NDT) is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage. As one of unconventional NDT technology, laser ultrasonic technique (LUT) have played an important role in inspecting the materials in some extreme environments, such as high temperature, high pressure, corrosion, radioactive and etc. LUT uses lasers to generate and detect ultrasonic waves in a noncontact way. Thus, compared with the traditional ultrasonic technique, LUT has the advantages of high precision, high sensitivity without requirement for geometry of target material. So far, LUT has been well applied to composite inspections for the aerospace industry and on-line hot tube thickness measurements for the metallurgical industry. This talk describes the application of LUT on flaws detection in rail and thermal barrier coatings.

Pulsed Eddy Current Nondestructive Testing for Defect Evaluation and Imaging of Automotive Lightweight Alloy Materials

Rapid and accurate damage detection of magnesium-aluminum alloy, which is an important material for automotive lightweight, is of great significance. Pulsed eddy current (PEC) is an effective electromagnetic nondestructive testing and evaluation (NDT&E) technique for metal materials. Metal loss evaluation and imaging are one of the most important steps in quality control and maintenance of key components of automobiles. A PEC method based on a rectangular excitation coil and an axial parallel pickup coil is proposed and investigated for the purpose of metal loss evaluation and imaging. Metal loss type of defects with different sections is designed and detected using line scanning technique and C-scan imaging in two scanning directions. Experimental results have illustrated that metal loss depth can be estimated effectively by the peak amplitude of PEC A-scan response. Then, the quantification information of metal loss depth is preliminarily obtained based on the linear fitting equation. Consequently, metal loss evaluation is realized by line scanning peak waves and C-scan pseudo 3D images. At last, the sensitivity comparison shows that the metal loss can be detected in both directions. The proposed method is an effective approach to evaluate the image surface-breaking metal loss in automotive lightweight alloy materials.

Ultrasonic Image Enhancement to Internal Defect Detection during Material Inspection

Ultrasonic waves are efficiently exploited to detect internal defects such as cracks and occlusions in non-destructive testing (NDT) of materials. In some automated procedures, emitter and receiver probes are displaced step by step and signals are displayed to form images that make diagnosis easier to interpret. However, too much images are unnecessarily stored when they correspond to safe zones (without presented defects). In this paper, we propose a method that enhances ultrasonic images quality in order to improve the discrimination between images containing or not a shape regarding a detected defect. The method is based on the adapted histogram equalization technique followed by morphological operations that erase all useless shapes on processed images.

Study on Attenuation Properties of Surface Wave of AE Simulation Source Based on OPCM Sensor Element

It is of great significance to grasp the ultrasonic attenuation characteristics of materials for the nondestructive testing of materials. The dynamic properties of a piezoelectric composite material (OPCM) with self-developed transverse anisotropy have been analyzed using the experiment in this work. The OPCM sensor is attached to the surface of the iron plate and concrete structures to sense the surface waves generated by acoustic emission (AE). The experiment results show that OPCM sensor elements have unique advantages compared to piezoelectric ceramic materials (PZT). Further, by comparing the signals of isotropic and anisotropic materials, the attenuation characteristics of surface waves propagating in different materials are studied, and a new method for measuring the attenuation coefficient of surface waves is demonstrated.

Fretting Fatigue Cracking of an Arresting Feature in a Turbine Disk of a Heavy-Duty Gas Turbine Engine

Abstract A check for surface cracks under application of the magnetic flux leakage method (MT testing) was performed on the turbine wheel disk of a heavy-duty turbine gas turbine engine for energy generation. It revealed unacceptable findings on the bearing surface of the sealing plate groove. In order to identify the damage-causing mechanism of the material, a metallographic examination was performed. The findings during non-destructive material testing were caused by a gaping material separation which was also easily detectable to the naked eye. The material separation is a high-cycle fatigue crack induced by fretting. Hence, the damage causing mechanism was fretting fatigue cracking.

Thermal nondestructive testing of materials and products: a review

The history of thermal nondestructive testing and infrared thermography is briefly reviewed. The state-of-the art of thermal testing with a focus on its applications to testing of composite materials in aerospace industry is described.

Sparse Representations to Replace TOFD Images in Non-destructive Testing of Materials

This paper describes a proposed method for the selection of relevant samples of ultrasonic signals during automatic material inspection. Instead of the well-known time of flight diffraction (TOFD) images, data are stored as a sparse matrix in which the elements only indicate whether a defect has been detected. This technique avoids storage of useless signals received during probe displacement in cases of low and high signal-to-noise ratios that correspond to coarse-grained and fine-grained materials, respectively. The approach is based on comparing the positions of maximum amplitudes, which are randomly located when signals only consist of noise but are in the same signal range when a defect is detected. The matrix elements are then applied as inputs to a self organizing map by neural networks to produce a normalized sparse matrix as the output, with a constant number of elements. This approach will be beneficial to enable the use of selected data in intelligent systems requiring a fixed number of inputs to characterize defects.

InfraRed Non-Destructive Testing of Glass Fibre Reinforced Composite Material for Detection of Sub-Surface Delamination

InfraRed Non-Destructive Testing of Glass Fibre Reinforced Composite Material for Detection of Sub-Surface Delamination

Detection and characterization of elongated bubbles and drops in two-phase flow using magnetic fields

We report a method to detect and to measure the size and velocity of elongated bubbles or drops in a dispersed two-phase flow. The difference of the magnetic susceptibilities between two phases causes a force on the interface between both phases when it is exposed to an external magnetic field. The force is measured with a state-of-the-art electromagnetic compensation balance. While the front and the back of the bubble pass the magnetic field, two peaks in the force signal appear, which can be used to calculate the velocity and geometry parameters of the bubble. We achieve a substantial advantage over other bubble detection techniques because this technique is contactless, non-invasive, independent of the electrical conductivity and can be applied to opaque or aggressive fluids. The measurements are performed in an inclined channel with air bubbles and paraffin oil drops in water. The bubble length is in the range of 0.1–0.25 m and the bubble velocity lies between 0.02–0.22 m s−1. Furthermore we show that it is possible to apply this measurement principle for nondestructive testing (NDT) of diamagnetic and paramagnetic materials like metal, plastics or glass, provided that defects are in the range of 10‒2 m. This technique opens up new possibilities in industrial applications to measure two-phase flow parameters and in material testing.

Opportunity estimation of optical method application in problem of kinematic characteristics registration of dynamic indenting process

Subject of Research.A stereoscopic method of technical vision is proposed for recording the kinematic characteristics of the dynamic indentation process in determining the physico-mechanical properties of materials. The proposed method makes it possible to determine the values of the indenter motion speed with high accuracy. Method. The method is based on the use of two high-speed video cameras immovably fixed on one flat platform. Cameras allow for synchronous recording of the indentation process. The objectives and orientation of cameras in the stereo system provide intersection of the visual fields and the required depth of the image space field. Measurement of the movement speed is performed by triangulation method. The distance between the conjugate points of the recorded object on the stereo images is inversely proportional to the distance between the pair of cameras and the corresponding point of the object in the three-dimensional space. Based on the analysis of images obtained by spatially separated cameras, the coordinates of the object point are determined. Main Results. The experimental setup consisted of two high-speed monochrome camcorders Evercam 4000-32-M, rigidly fixed through stereo. Synchronous recording was kept at a speed of 4000 frames/s with a resolution of 1280 × 860 pixels. The indenter was made in the form of a steel ball with a mass of 230 g with a diameter of 38 mm and fell onto an aluminum disk 10 mm thick from a height of 310 mm. Video images from cameras were transferred to a personal computer for processing. The analysis of the obtained data was carried out in the MATLAB system with the help of a specially written software module. The sensitivity of the proposed method made it possible to determine confidently the values of the maximum approach speed of a steel ball equal to 2.39 m/s and a rebound velocity of 1.2 m/s. The random component of the method error did not exceed 2.5%. Practical Relevance. The development of this approach will enable to create high-precision sensors of dynamic indentation. The research results may be of interest to specialists involved in metrological support and non-destructive testing of materials and products in various fields of engineering and construction.