The Largest Open Access Portal of Nondestructive Testing (NDT)

Neutron and X-ray beams provide unique, powerful and non-destructive access into the heart of materials and components, over length scales ranging from the centimetre to the atom. The Institut Laue-Langevin ILL – Europe’s leading neutron source - and the ESRF – Europe’s leading synchrotron light source, combine 80 experimental stations providing neutron and X-ray beams with exceptional properties to overcome the limitations of standard laboratory characterisation techniques. Regarding challenges in the aeronautic and space sectors, we will detail some advantages obtained by synchrotron and neutron beams in stress mapping and computed tomography. The ESRF’s high-energy synchrotron X-rays can map efficiently the strain and stress at the surface and up to several hundreds of microns below to give depth profiling with high spatial resolution. Neutrons give access to the full stress tensor from 60μm below the surface up to the interior of the component (e.g. 30 cm in Al, 6 to 7 cm in Ti, Ni or steel). Both techniques are able to measure in real time and non-destructively the stress distribution during mechanical loading, or during heating/cooling processes. A current exciting development is the investigation of residual stress build-up during additive manufacturing. Here, we will show examples of measurements taken from aircraft and satellite components. Note that a combination of neutron and X-ray datasets can be offered by the institutes. With regards to computed tomography, synchrotron X-rays and neutrons provide complementary information. Synchrotron X-rays provide remarkable insights into materials up to the nanoscale with a resolution as high as 30 nm. At the microscale, synchrotron X-rays enable vastly more accurate (eg. with phase contrast imaging and lower beam hardening effect) and faster data collection than lab equipment – 2D radiography can be performed at MHz rate for monitoring rapid phenomena and 3D CT can be done at ~Hz speed. With these capabilities, it is possible to monitor dynamic processes in real time (e.g. crack propagation, exploding fuse or bed fusion in additive manufacturing). Neutron tomography makes use of the specific properties of thermal neutrons to penetrate deeply a large majority of materials (e.g. most metals) whilst being highly sensitive to other elements, notably hydrogen and lithium, enabling the imaging of water, polymers or explosive charges embedded in metallic structures, without metal induced image artefacts neither radiation damage. We will conclude our presentation by briefly showing how further neutron and synchrotron X-rays techniques can address issues in composites, electrical components and radiation

It is a state of the art to test concrete specimen with ultrasonic-based methods. However, due to the density and the required high resolution, the testing is done with high-frequency waves which cannot penetrate the structure in depth. Adopting techniques used, e.g., in geotechnical applications, a model-based inversion using higher wavelengths is proposed, which is the full waveform inversion. This approach is however non-linear, time-consuming and highly ill-posed. Thus, further developments are necessary to make the technique applicable to structures like dams, dikes or similar. Among these developments are further accelerations of the so-called forward codes by a more efficient implementation of the wave equation. To handle with the ill-posedness, regularization techniques need to be applied and tested in order to reduce the risk of incorporating too many and misleading artifacts in the resulting images. This, e.g., can be done by the consideration of a priori knowledge of the material properties inside a structure which could be taken from already well-established inspection methods. Some first results, mainly based on synthetic data, will be presented to show the capabilities of the model-based approach.

The containment liner plate (CLP) in a nuclear power plant is the most critical part of the structure of a power plant, as it prevents the radioactive contamination of the surrounding area. This paper presents feasibility of structural health monitoring (SHM) and an elastic wave tomography method based on ultrasonic guided waves (GW), for evaluating the integrity of CLP. It aims to check the integrity for a dynamic response to a damaged isotropic structure. The proposed SHM technique relies on sensors and, therefore, it can be placed on the structure permanently and can monitor either passively or actively. For applying this method, a suitable guided wave mode tuning is required to verify wave propagation. A finite element analysis (FEA) is performed to figure out the suitable GW mode for a CLP by considering geometric and material condition. Furthermore, elastic wave tomography technique is modified to evaluate the CLP condition and its visualization. A modified reconstruction algorithm for the probabilistic inspection of damage tomography algorithm is used to quantify corrosion defects in the CLP. The location and shape of the wall-thinning defects are successfully obtained by using elastic GW based SHM. Making full use of verified GW mode to Omni-directional transducer, it can be expected to improve utilization of the SHM based evaluation technique for CLP.

The majority of engineering materials are polycrystalline. Their properties and performance strongly depend on the 3D microstructure in a sense that the individual grains, their crystallographic orientations, their size and shape as well as their spatial distribution ultimately determine the material’s behavior under use. Characterizing such microstructure through x-ray diffraction contrast tomography was for long time only possible at large scale synchrotron facilities; involving both intricate data acquisition schemes and demanding data analysis and reconstruction approaches. The novel lab-based diffraction contrast tomography (LabDCT), operating on a commercially available x-ray microscope, made this capability available in the home laboratory [1]. In addition, the highly demanding analysis and reconstruction requirements were made accessible in a straightforward workflow, enabling non-expert users for this advanced imaging modality. Combination of LabDCT with conventional absorption microCT enables a wide range of microstructural features to be characterized simultaneously and provides complementary information about the observed microstructure. Permitting wide accessability and routine use of diffraction contrast tomography allows for non-destructive, time-evolution studies of dynamic microstructural evolutions and materials characterization. Aside from introducing the fundementals of the technique and its implementation on a laboratory scale, we will present a number of LabDCT applications for industry relevant materials characterization cases. To highlight and demonstrate the technique’s capabilities these application cases include corrosion of metals, photovoltaics [5], metals development [2][3], additive manufacturing and steel processing [4].

Dual energy X-ray imaging is undoubtly advantageus in several aspects. Nevertheless it is not a much used method industrially, being, actually, a rather exotic technique. Some of the disadvantages are the necesity or performing two tomographic experiments at different energies and/or using different filters. This extends the tomography time up to double of a conventional tomography. In addition as tomographies are done as separate experiments it may happen that sample or focus position is little different, thus ruining the required spatial correlation. New direct detection matrix detectors overcome these current inconveniences and provide high S/N and fast acquisition, althought they are still not much considered industrially, may be because of the reduce size of most of these detectors.

Industrial rotational laminography systems are "rare" X-ray devices, conventionally "doomed" to perform a very specific operation due to its very specific desing and components layout. Expensive and high quality components are settled in such a way the system cannot perform microCT examinations. Due to its high specificity, rotational laminography systems are not the "best-seller" models in any of the X-ray systems manufacturers. A compact and versatile X-ray microCT and laminography prototype has been developed for multipurpose laboratory materials research. The system is composed by a microfocus X-ray tube (5 microns spot size, 100kV, 200μA), flatpanel detector (2K, 50 microns, 12bits) and a 4 axis system composed of a X translation system of 500mm for varying SOD experiments, Z-stage of 50mm range, a goniometer of ±40º range and a piezoelectric rotation table (22mm heigh, ID aperture of 102mm and excentricity <2microns). This hardware combination provides excellent spatial resolutions up to 2.4 microns and can be installed in a small cabinet of 800x500x500mm. The system allows local examination of slab samples up to 200x200mm and FOVs up to 90x90mm. Additionally XY piezoelectric micropositioner can be installed complementarily over the rotation stage as a helpful tool for high resolution microCT experiments. This system is an optimum solution for researchers and companies in the field of GF and CF materials (production, postimpact characterizacion…), adhesion, electronics and 3D printing fields.

Faster tomographic methods are required both in the R&D and industrial fields. Actually in the last years it has been possible to perform 4D studies and beat the minute threshold (full scan time) at reasonable image quality. Currently some comercial equipments can perform these studies at the schocking speed of 20s per tomogram. New hardware developments such as direct detection detectors with much better QE factors could probably improve these current, very meritory, "records". Nevertheless have to consider that 4D data sets are heavy, complex to analyze and, undoubtly cannot be reconstructed, examined nor analyzed in real-time.

Aluminum alloy has been widely used as the structural materials in the aerospace industry due to their high specific strength, good corrosion resistance and excellent processability. However, corrosion of alloy materials often causes severe consequences. For engineering structures, the failure often occurred in the near-hole area. Corrosion damage is one of the main types of damage in aluminum structures, and the corrosion damage in near-hole area will accelerate the failure of the structure. Although there are some studies on the monitoring techniques of single-hole-edge corrosions up to now, few researches referred to how to monitor the multi-hole-edge corrosion damage due to the complex boundary reflection and Lamb wave dispersion characteristics. Thus, an effective technique for monitoring the corrosion damage at multi-hole especially in complicated structures is urgently needed. This study presents a novel monitoring method for hole-edge corrosion damage in aluminum plate structures based on Lamb wave tomographic imaging technique. An experimental procedure with a cross-hole layout using 32 piezoelectric transducers (PZTs) was designed. Six holes in three rows and two columns were evenly processed on the raw plate. The A0 mode of Lamb wave was selected, due to its sensitivity to the thickness-loss damage. The iterative ART method was used to locate and quantify the corrosion damage at the edge of the hole. The hydrofluoric acid with the concentration of 20% was used to corrode the specimen artificially. To estimate the effectiveness of the proposed method, single-hole and double-hole corrosion monitoring were both conducted on multi-hole plate. The frequencies of Lamb wave were selected from 50kHz to 200kHz. The predicted corrosion damages based on the tomographic method with 16 different frequencies of Lamb wave were compared with the real corrosion damage. Firstly, for single-hole-edge corrosion monitoring, it could be concluded that Lamb wave of 90kHz was more applicable to corrosion prediction. Then, for double-hole-edge corrosion monitoring under the same conditions, the considerable light leakage was observed owing to the excessive edge reflection caused by the existence of another hole. However, in spite of the light leakage, the position and size of corrosion spots were still able to be predicted. The results indicated that the Lamb-wave-based tomographic method can be used to monitor the multi-hole corrosion damage accurately.

Digital Detector Arrays enable an extraordinary increase of contrast sensitivity in comparison to film radiography. The increased sensitivity of digital detectors enables the efficient usage for dimensional measurements and functionality tests substituting manual maintenance. The digital measurement of wall thickness and corrosion status is state of the art in petrochemical industry. X-ray back scatter techniques have been applied in safety and security relevant applications with single sided access of source and detector. First inspections of CFRP in aerospace industry were successfully conducted. Computed tomography (CT) applications cover the range from nm to m scale. Small structures of integrated circuits are visualized and measured with lens based CT-systems or at synchrotrons. Phase contrast imaging provides enhanced structure contrast in micro radiography and micro CT. The scope of typical CT applications changes from flaw detection to dimensional measurement in industry substituting coordinate measurement machines. Mobile computed tomography is applied for in-service radiographic crack detection and sizing of welded pipes in nuclear power plants and for NDT of large CFRP structures in aerospace applications. New specialized high energy CT devices have been laid out for inspection of complete cars before and after crash tests. High speed applications with flash tubes permit the 3D measurement of fast process dynamics including car crash visualization. Digital radiography techniques, computed tomography and computed laminography designs are nowadays developed by numerical simulation before hardware construction. New X-ray source concepts based on laser wake field acceleration permit further reduction of spot sizes and minifocus high energy applications.

Synchrotron X-ray diffraction is a powerful non-destructive technique for the analysis of the material stress-state. High cooling rates and heterogeneous temperature distributions during additive manufacturing lead to high residual stresses. These high residual stresses play a crucial role in the ability to achieve complex geometries with accuracy and avoid distortion of parts during manufacturing. Furthermore, residual stresses are critical for the mechanical performance of parts in terms of durability and safety. In the present study, Ti-6Al-4V bridge-like specimens were manufactured additively by selective laser melting (SLM) under different laser scanning speed conditions in order to compare the effect of process energy density on the residual stress state. Subsurface residual stress analysis was conducted by means of synchrotron diffraction in energy dispersive mode for three conditions: as-built on base plate, released from base plate, and after heat treatment on the base plate. The quantitative residual stress characterization shows a correlation with the qualitative bridge curvature method. Computed tomography (CT) was carried out to ensure that no stress relief took place owing to the presence of porosity. CT allows obtaining spatial and size pores distribution which helps in optimization of the SLM process. High tensile residual stresses were found at the lateral surface for samples in the as-built conditions. We observed that higher laser energy density during fabrication leads to lower residual stresses. Samples in released condition showed redistribution of the stresses due to distortion.

The digitalization of irreplaceable objects of cultural and/or historical significance as field of research is gaining more and more importance recently. The Germanisches Nationalmuseum (GNM) in Nürnberg, Germany, and the Development Center for X-ray Technology (EZRT) of the Fraunhofer Institute for Integrated Circuits (IIS) in Fürth, Germany, were jointly working in the MUSICES project, addressing issues of 3D-digitization of historically important musical instruments. This project was funded by the German research association DFG (Deutsche Forschungsgemeinschaft) and ends in January 2018. The project partners drew up examination standards that, independent of the deployed devices and operating staff, are set to deliver high-quality 3-D volume data sets representing musical instruments. Plenty of representative examples carried out during the project ensure the applicability of the technical parameters. MUSICES has been dealing with testimonials of the manufacturing of musical instruments during the last five centuries. From 2015 to 2017, more than 100 historically remarkable objects in the collection of the GNM were digitized my means of fully 3-dimensional image acquisition with X-ray CT The CT measurements were performed at the EZRT site in Fürth, where X-ray systems with maximum radiation energies of between 60 and 9,000 keV are used for CT scanning and reconstruction, as well as means for multispectral material analysis and algorithms for the correction, visualization and evaluation of image data. Several methods were applied to optimize CT parameters via extended studies of simulated virtual data sets. Based on the evaluation of all acquired 3D-images, standard procedures are proposed. The image data itself are made available to the broad public. Additionally, the final report provides various checklists for preparation, transport, positioning, best practice for measurement of various classes of instruments (wood/metal/mixed/other resp. size and shape), an elaborate data base structure description for long term archiving and methods for detailed image quality assessment.

Post-impact structural performance of a laminated composite is a concern for aerospace and other advanced industries. Low-velocity impact may cause barely visible but considerable internal damage in structures, which is difficult to detect. To identify and accurately characterize such localized damages, efficient non-destructive evaluation methods are required. In this study, the potential of guided wave tomography to quantify the changes in material properties of a quasi-isotropic composite with a stiffness defect is investigated. The method reconstructs the velocities of guided waves by the inversion of ultrasonic signals captured by a transducer array around the inspection area. The resulting velocity maps are then converted to specific elastic constant maps by the material dependent dispersion characteristics of selected guided modes. The reconstruction is based on a full-waveform inversion algorithm and was implemented on the data obtained from finite element simulations. The sensitivity analysis showed that the Lamb mode A0 is suitable for the determination of effective in-plane Young’s modulus and out-of-plane shear modulus. The reconstruction of these parameters can be decoupled by considering varying sensitivity of the velocity depending on material properties at different frequencies. Numerical results on a localized defect with reduced elastic constants illustrate the interest of this strategy.

This paper deals with the structural quality assessment of composites structures during their life cycle. Thus, this talk will start by a presentation of the main Non Destructive Testing methods preconized during composite prototypes qualification. The benefits of X-ray computed Tomography and Acoustic Emission will be illustrated thanks to industrial projects addressing among others the qualification of composite bearing cages and of a composite crane boom. Then, we will focus on applications dealing with online inspection of composite structures production. An ultrasonic phased array inspection method was developed in order to monitor continuously the integrity of a pultruded thermoplastic tape during its manufacturing. This system has to detect lacks of resin impregnation and dry fibers in real time with an inspection cadency in agreement to industrial requirements. Finally, infrared thermography systems will be presented for the monitoring of the thermoplastic 3D filament winding process (SPIDE TP) and of the Quilty Stratum Process (QSP). The objectives of these systems are respectively to detect disbonds, inter-tape porosities… following the thermoplastic tape welding (SPIDE TP) and to check the temperature distribution on the thermoplastic lay-up preform before press-forming (QSP).

The determination of lengths is one of the tasks in the dimensional measurements. Using tactile coordinate measurement machines (CMMs), we can find the length using two states: there is either contact with the surface or no contact, and the length is the difference between two contact points. In contrast, using X-ray computed tomography (CT), the information is included in volume element (voxel) positions, sizes and grey values. Latter usually are estimated absorption coeffcients at the respective coordinates, averaged over the specifc element. Hence, the information where specifcally in this element the absorption occurs is unknown. Furthermore, there are many influencing factors which also alter the estimation of absorption, like scattering and beam hardening, the used spectrum of the X-ray source, and the absorption spectrum of the detector or the number of used projections. Those properties can be shortly described as -image quality- if we understand the tomogram as a three dimensional image, resulting from the CT. Due to all of those factors, the surface is not as well defined as with CMMs. As a lot of those factors are usually properties of the individual scan and arise from the object itself, it is problematic to transfer results of the study of test artefacts onto the -real- objects. Therefore it sometimes can be more useful to analyse the local grey value distribution to determine an uncertainty of the length measurement, rather than transferring results from the tactile standards to dimensional measurement in X-ray CT. Especially, if we are interested in the lengths, it can be important to study the local edge responses (which is the influence of an edge of the scanned object onto the tomogram), as the length can be described as the distance between two edges. In this paper, we discuss this relationship with exemplary tomograms.

In industrial Computed Tomography (CT) the state-of-the-art reconstruction method for cone-beam CT is the well-known algorithm developed by Feldkamp, Davis, and Kress (FDK). Beside this standard several alternative strategies exist which involve certain advantages depending on the application of interest, e.g. the usage of prior knowledge or arbitrary trajectories by using algebraic reconstruction techniques (ART). These approaches have a higher computational complexity compared to the FDK. However, with the increasing computational power in the last years, these reconstruction techniques become more and more applicable. Regarding metrology there are two main influencing factors for accurate measurement results: the projective geometry and the imaging chain. The quality of the projective geometry can be measured by SD and the image quality for example by the modulation-transfer-function (MTF) and contrast-discrimination-function (CDF) following ASTM E 1695. The last part of the imaging chain is the volume reconstruction method. Especially for bidirectional measurement the internal or external boundary surface has to be determined very accurate. Potential X-ray imaging artifacts due to certain material and object shape influences will lead to distortion of the found boundary surface. If a new algorithm is used these distortions might change and it is important to know the expected effect on the final measurements. In this extended abstract the results of an ART reconstruction are compared with the FDK-results regarding the quality of the projective geometry and the imaging chain as well as varying the number of projection images. Based on this comparison a conclusion is possible how metrological applications may be influenced by a chance of the reconstruction strategy and a reduction of the number of images.

Modern automotive and car body design is characterized by a combination of a large number of materials and a wide variety of joining techniques. A car body of current design has 5000 - 6000 joining elements, which have to be fully tested and evaluated along the production process. Recently, mainly destructive methods are used for testing which are characterized by a high workload and the loss of value of already produced parts. Well-established equipment for 3D non-destructive testing are ground based, fixed X-ray computed tomography (XCT) systems. However, with this kind of systems, setting up measurements of large assemblies for automated scanning requires a demanding hardware setup and is quite time consuming. A system which allows flexible positioning and fast non-destructive inspection would be beneficial not only for quality control in automotive production but also for aerospace or energy industry applications. For that reason, a completely new XCT system has been developed. The most important requirement for the design has been the need for carrying out a local tomography of regions of interest (ROI) of open frame structures. The kinematic process of tomography is implemented by a “U”-shaped XCT unit equipped with an automated rotating arm. For automation, the XCT unit is mounted on an industrial robot. After approaching a predefined position with the robot, the XCT unit will start a scan by rotating the scan arm around 360°. Radiographic projections are measured continuously and reconstructed to a 3D data set within minutes. Resulting CT-Images measured with the developed XCT system show that it enables non-destructive testing of the complete set of joining elements at any position of a car body. With the system, measurement time per joining element and loss of value are minimized by eliminating the need for sample preparation.

To perform experiments on the Laser Megajoule (LMJ) [1, 2], the Laser Targets Department of CEA (commissariat à l’énergie atomique et aux énergies alternatives) builds up and develops targets with dimensional specifications ranging from nanometric to millimetric scale. Additive manufacturing becomes an important process to realize target element or target assembly tools. To match stringent specifications, accurate systems of characterization are used to characterize targets and manufactured micro-tools. Micro X-Ray computed tomography is a powerful instrument of control and acquisition of information for manufactured products. This technology can be useful in the validation of geometric parameters which are difficult to obtain with other metrology systems. It allows characterizing internal defects volume and geometry. The obtained tomographic volume is analysed with a post processing visualization tool. This works highlights improvements of the characterization of 3D printed micro-tools, with complex shape by computed tomography. Results are presented and detailed.

Especially in aeronautic and space industry it is important to produce carbon fibre-reinforced polymers (CFRP) with very low porosity since there is a direct relation between porosity and mechanical properties, such as shear strength. Typical acceptable porosity values are in the range of < 2.5 vol.%. The most common non-destructive method for measuring the porosity is ultrasonic testing (UT) assuming there is a linear correlation between ultrasonic attenuation and porosity. However, the ultrasonic attenuation coefficient depends not only on the porosity, but also on the shape and distribution of the pores, the presence of other material inhomogeneity’s and the individual material system. This can lead to significant errors in the determination of the porosity. Acid digestion and materialography are mainly used as reference method, but both methods are destructive, time-consuming and inaccurate. This paper deals with the application of X-ray computed tomography (XCT) methods as reference for quantitative evaluation and characterization of porosity in carbon fibre-reinforced composites. The degree of accuracy strongly depends on several material and XCT parameters: • Material parameters: woven fabric or unidirectional material, additional glass fibres or copper wires for lightning protection, higher dense epoxy used for adhesive bonding, etc. • XCT parameters: resolution and voxel size (VS), used XCT device and modality (e.g.: cone beam XCT vs. Talbot Lau grating interferometer XCT), threshold method, etc. In this contribution several mentioned parameters influencing the quantitative evaluation of porosity in CFRP are discussed and different types of CFRP with porosity are presented. Porosity values gained with XCT methods are compared with UT, acid digestion or materialography.

In this contribution, high-resolution X-ray computed tomography (XCT) results of various inhomogeneous samples including a poplar wood sample, a carbon fibre reinforced polymer sample and an AlSiCu light metal alloy are presented. These samples have been acquired with a new lab-based nano-XCT device equipped with a nano-focus X-ray tube and two different detector systems. Depending on the material system and the measurement task, the user has to choose between these two detector types that can be exchanged by a quick mounting system. Limitations on resolution and contrast-to-noise ratio (CNR) are discussed qualitatively and quantitatively for selected measurements and evaluation tasks. Structures between 500 and 700 nm could be clearly resolved. In addition the positioning accuracy of the exchangeable flat panel detector is investigated. Detector repositioning shows high reproducibility, but systematic measurement errors are in the range of half of a voxel for repeated scans of a calibrated ball bar phantom with a system voxel size of (3 µm)³.

Forschungszentrum Jülich is one of Europe's largest interdisciplinary research centers, working in many scientific areas. The Institute of Energy and Climate – Fundamental Electrochemistry (IEK-9) focuses on the development of materials for electrochemical storage and energy conversion. The Central Institute for Engineering, Electronics and Analytics – Engineering and Technology (ZEA-1) has capabilities in mechanical and electronics development, as well as analytical services. The development of measurement and testing methods is one of the ZEA-1 focus areas. Solid-state lithium-ion batteries are an emerging topic in the field of battery research because these materials promise to solve safety issues in current lithium-ion batteries. One of the critical problem for this system is volume expansion/contraction of active materials like anode and cathode, which may impede their direct incorporation into solid-state batteries. The scientific problem under this study is experimental investigation of cracks formation and evolution in a bulk-type solid-state battery during different loads and at different electrochemical stages. It appears that the one suitable approach is an application of non-destructive method of X-ray computed tomography (CT). With the help of CT, we are able to detect the issue of possible cracks propagation and their characterization in the solid electrolyte material. The morphology of the interfaces of battery components are also the topic of current studies. This could help to find the optimal correlation between mechanical and electrochemical properties for the practical application of solid-state battery. To carry out the measurement noted above, the newly upgraded industrial CT equipment at the Institute ZEA-1 was applied. The preliminary ex-situ studies of first prototypes of cycled batteries by X-ray CT have indeed found clearly the appearance of cracks in the volume. In-situ measurements during cycling will be performed. The visualized correlations of electrochemical properties, microstructure and mechanical characteristics of bulk-type solid-state batteries are presented and discussed.