Talbot–Lau grating interferometry is a new innovative X-ray technology in the field of radiography and computed tomography that extends the imaging capabilities of absorption contrast (AC) in medicine and material science by the introduction of differential phase contrast (DPC) and dark-field contrast (DFC). This paper discusses the benefits of the additional imaging modality of DFC provided by a new desktop Talbot–Lau μXCT system (SkyScan 1294). With this system, selected medical and biological samples such as medical foam, cortical bone, molar tooth, and barley corn seed samples have been imaged and compared to reference methods such as high-resolution μXCT and optical coherence tomography (OCT) regarding information gain and contrast.
•The impact of near field characteristics of antennas on high resolution microwave based NDT is analysed.•Antenna concepts for microwave based NDT were evaluated regarding spatial resolution, penetration depth and return loss.•Near field simulations are verified using the Electromagnetic Infrared Method.•Horn antennas with perforated metal aperture are able to produce high resolved images at a certain depth of the DUT.•The focusing characteristics of horn antennas with delay lens and reduced aperture size are permittivity independent.
In this study, X-ray phase contrast imaging with a grating interferometer is applied on pearls for the first time in order to distinguish natural pearls from cultured pearls. Traditionally, this separation is mainly based on X-ray radiography. In order to visualize the internal structure of pearls we used a custom-made grating interferometer setup and performed measurements on three different pearl products, a natural pearl, a beaded cultured pearl and a beadless cultured pearl. To enhance the visibility of the internal pearl structures, we applied a high-pass filter in order to better conclude on the applicability of this technique to the separation of natural and cultured pearls. The study shows that it is possible to visualize internal pearl structures using distinctly shorter exposure times compared to traditional X-ray radiography and that X-ray phase contrast imaging is a promising complementary method for pearl analysis.
This paper discusses vibration serviceability assessment of a highly trafficked local footbridge based on the experimental tests and analytical studies. The selected bridge is an approximately 60 m (196 ft) long multi-span steel structure with a continuous reinforced concrete slab supported on two longitudinal steel girders. The experimental study consists of ambient vibration and pedestrian interaction tests to describe the dynamic characteristics of the selected bridge structure. The fundamental frequency of the bridge in the vertical direction obtained through ambient vibration tests was within the critical range described by available design guidelines. This required further analysis to assess the performance of the bridge relative to the maximum acceleration thresholds. In addition to the peak dynamic response obtained from the pedestrian interaction tests, peak acceleration values were calculated analytically based on current design guidelines and compared to the comfort limits. Results from both experimental and analytical studies suggest that the footbridge possesses satisfactory serviceability performance under low and dense traffic conditions, but the comfort level under very dense traffic loads was classified as minimum according to the results of the analytical calculations.
In this paper, we present the results of a failure analysis done on new heat exchanger tubes, which shows loss of thickness during a EC inspection to stablish a prior loss of thickness base line aiming guarantee fitness for service during its working life. The root cause analysis indicates that there is intergranular corrosion due a differential concentration caused by seawater evaporation inside the tubes during the ship transit from the port of origin in China to the destination port in Brazil.
The health status of a railway tunnel should be regularly inspected during its service period to ensure safe operation. Ground-penetrating radar (GPR) has been used as a key technique for tunnel detection; however, so far, the measurements of GPR are only obtainable in contact mode. Such methods cannot meet the requirements of the operational tunnel disease census and regular inspections. Therefore, a new method—vehicle-mounted GPR with long-range detection—has been developed. It consists of six channels. The distance from its air-launched antenna to the tunnel lining is approximately 0.93 m–2.25 m. The scanning rate of each channel is 976 1/s. When the sampling point interval is 5 cm, the maximum speed can reach up to 175 km/h. With its speed and air-launched antenna, this system has a significant advantage over existing methods. That is, for an electrified railway, there is no need for power outages. Indeed, the proposed system will not interrupt normal railway operation. Running tests were carried out on the Baoji–Zhongwei and Xiangfan–Chongqing railway lines, and very good results were obtained.
The purpose of the presented work was to undertake experimental trials to demonstrate the potential capabilities of a novel in-situ robotic ultrasonic scanning technique for measuring and monitoring loss of the cladding wall thickness in fuel pins of Advanced Gas-cooled Reactors using non-radioactive samples. AGR fuel pins are stainless steel cylindrical ribbed pipes of inner diameter of the rod being about 15 mm and wall thickness of about 300 μm. Spent AGR fuel pins are stored in a water pond and thus may be prone to corrosion and stress-corrosion cracking under adverse conditions. An ultrasonic immersion transducer with central frequency of 25 MHz was used to measure wall thickness of the AGR fuel cladding. The novelty of the approach consists in the usage of a frequency domain technique to measure the wall thickness combined with cylindrical ultrasonic scanning of the samples performed using an industrial robotic manipulator. The frequency domain approach could detect wall thicknesses in the range 96 μm to 700 μm with a resolution of about 10 μm. In addition to the frequency domain measurements, using conventional time domain techniques, it was possible to detect very short (2.5 mm long) and shallow (100 μm in depth) crack-like defects in the fuel cladding.
The possibility of measuring multi-material components, while assessing inner and outer features simultaneously makes X-ray computed tomography (CT) the latest evolution in the field of coordinate measurement systems (CMSs).
This paper presents a comparison of surface-based and image-based quality metrics for dimensional X-ray computed tomography (CT) data. The chosen metrics are used to characterize two key aspects in acquiring signals with CT systems: the loss of information (blurring) and the adding of unwanted information (noise). A set of structured experiments was designed to test the response of the metrics to different influencing factors. It is demonstrated that, under certain circumstances, the results of both types of metrics become conflicting, emphasizing the importance of using surface information for evaluating the quality dimensional CT data. Specific findings using both types of metrics are also discussed.
Laser Sintering (LS) is an Additive Manufacturing (AM) technology for polymers processing which is increasingly being used to produce functional products with designs not achievable with traditional manufacturing technologies. Lightweight cellular structures are a good example of complex designs which are increasingly finding applications in AM parts. However, it is not yet clear how the LS process affects the porosity and geometrical characteristics of the cell structural elements. Getting this information allows to perform quality control of the LS process, gives insights into how to improve it, and might help to take into account manufacturing process variability during the design phase.
ISO/TC 213/WG 10 is responsible for creating international standards (series ISO 10360) for the acceptance testing of coordinate measuring systems (CMSs). A current topic is creating a future part of ISO 10360 for CMSs using dimensional computed tomography (CT). The discussion is focussed on how to include material thickness influence in acceptance testing. ISO/TC 213/WG 10 decided to perform an experimental survey to study this topic. This ISO test survey covers several national metrology institutes and manufacturers. Reference standards under study made of aluminium are two step cylinders provided by the National Metrology Institute of Japan (NMIJ), and two hole plates provided by the Physikalisch-Technische Bundesanstalt (PTB), Germany. To check for residual errors of CT-based CMSs, additional reference standards may be measured by participants. This report details results and experiences of the participant PTB. PTB applied scaling reference measurements of a multi-sphere standard and a printed circuit board as additional reference standards, i.e. in addition to hole plate and step cylinder measurements, respectively. Measurements were performed in mid 2015 using the PTB dimensional CT system (Nikon Metrology MCT225). In this contribution, special focus is placed on the interpretation of the results and the consequences of a potential testing regime. This text does not directly describe an existing ISO standard nor a published or intended ISO standard draft. It is intended to contribute to the research of influence parameters which are relevant for a possible future part of ISO 10360 for the case of CT-based CMS (which is assumed to be part 11).
This study demonstrates that 3D printing technology offers a simple, easy, and cost-effective method to fabricate artificial flaws simulating real cracks from the viewpoint of eddy current testing. The method does not attempt to produce a flaw whose morphology mirrors that of a real crack but instead produces a relatively simple artificial flaw. The parameters of this flaw that have dominant effects on eddy current signals can be quantitatively controlled. Three artificial flaws in type 316L austenitic stainless steel plates were fabricated using a powderbed-based laser metal additive manufacturing machine. The three artificial flaws were designed to have the same length, depth, and opening but different branching and electrical contacts between flaw surfaces. The flaws were measured by eddy current testing using an absolute type pancake probe. The signals due to the three flaws clearly differed from each other although the flaws had the same length and depth. These results were supported by subsequent destructive tests and finite element analyses.
A novel technique for the accurate measurement and adjustment of fracture apertures in digital images of fractured media is presented. We utilize X-ray micro-computed tomography to image a highly fractured coal sample and collect high-resolution scanning electron microscope (SEM) images from the samples surface to facilitate segmentation of coal fractures. The gray-scale micro-CT values at the mid-point of fractures are obtained and correlated to aperture sizes measured with the higher resolution SEM data. Afterwards, the micro-CT images are upsampled to enable assignment of aperture sizes smaller than the image resolution. We initially segment the coal image, upsample the segmented image, and then re-calibrate the fracture aperture sizes. The final calibrated segmented image contains the fracture network acquired from the micro-CT data with precise aperture sizes assigned based on the high-resolution SEM data. To illustrate the importance of accurate aperture measurement, two coal subsets are tested. The permeabilities before and after applying the calibration method are measured. The results show a significant change in numerical permeabilities after applying the calibration method. This indicates that a large amount of information is potentially omitted when utilizing standard image segmentation tools to segment fractured media.
Innovative ultrasonic instrumentation to be used for future Generation IV sodium-cooled fast reactors is currently being investigated. One potential option under study here is the monitoring of the sodium temperature at the outlet of the core by using ultrasound. The main advantage of ultrasonic setups is that they can be used far from the intended subassemblies. The idea is to send an ultrasonic beam at grazing incidence towards the (cylindrical) subassembly head, and to measure the ultrasonic time of flight between the two diametrically opposite edges, in order to estimate the mean temperature across the subassembly outlet diameter. Moreover, the grazing incidence could allow considering the simultaneous temperature monitoring of several aligned subassemblies. One of the main points to be considered is the interaction between the ultrasonic beam and the immersed target, which involves specular reflection and/or diffraction, both phenomena depending on the incidence angle and the target geometry. The present paper investigates this interaction, mainly from an experimental point of view. Different geometries of “2D” (plate) and “3D” (tube) edges are tested and compared under various incidence angles. The final aim is to identify an optimal ultrasonic configuration to perform thermometry at the outlet of an immersed tube.
This study evaluates the necessity of considering Transmitter–Receiver (T–R) offset distance for predicting pavement layer thicknesses from two-way travel time data captured by a Ground Penetrating Radar (GPR) antenna. For the purpose of this study, GPR testing was conducted at an instrumented pavement section at Milepost (MP) 141 on Interstate I-40 near Albuquerque, New Mexico, USA. The GPR system used for this study consists of 2.0 GHz air-launched, 900 MHz ground-coupled, and 400 MHz ground-coupled antennas. The entire instrumented test section was tested with different antenna configurations. The two-way travel time is used for calculating layer thicknesses using two approaches: one considering the T–R offset, which is a non-conventional approach and the other without considering the T–R offset, which is a conventional approach. Statistical analysis namely, t-test is performed on the predicted layer thicknesses from these two approaches. The analysis indicates that these two approaches are significantly different. The predicted thicknesses by these two approaches are compared to each other. It is observed that the approach considering the T–R offset predicts the layer thicknesses with better accuracy compared to the conventional approach. Therefore, it is recommended to use the T–R offset in predicting pavement layer thickness from GPR data.
This paper presents a Non-Destructive Testing (NDT) method based on the penetration properties of terahertz (THz) waves. A CW raster-scanning THz imaging setup, using a 3.8 THz Quantum Cascade Laser as a source, is used to perform NDT of polypropylene/polypropylene composite samples.
The deployment of additive manufacturing processes relies on part quality, specifically the absence of internal defects. Some of those defects have been associated with porosities in the powder feedstock. Since the level of porosity in the powder is generally very low, standard characterisation techniques such as pycnometry and metallography are not suitable for quantification. However, the quantification of such micro sized porosity in metallic powders is crucial to better understand the potential source of internal defects in final components and for quality control purposes. X-ray tomography with a 3 μm resolution offers the possibility to visualise pores in large volume of powder and to quantify their geometrical features and volume fraction using image analysis routines. This combination is unique and demonstrates the power of the approach in comparison to standard powder characterisation techniques. Results presented show the prospects and limits of this technique depending on the imaging device, material and image analysis procedure.
X-ray computed tomography displays a highly valuable nondestructive testing tool in various fields. A major disadvantage of this method comprises its high operating costs. Therefore, the reduction of the scanning times would be highly beneficial. Here, we demonstrate exemplarily for the testing of pearls the possibility to decrease the scanning times. The great diversity of pearls on the market, often of unclear origin, especially used for jewelry, demands non-destructive test methods for the fast and reliable classification and validation. We discuss the use of a nano-focus X-ray computed tomography (nf-XCT) system for fast three-dimensional characterization to distinguish between natural and cultured pearls. We test the approach not on individual pearls but for a more demanding task namely for a pearl necklace, that is multiple pearls on a strand. We show that with just one scan the 3D image data of the individual pearls within the whole necklace, which is composed of about 200 pearls can be scanned and reconstructed in only about 24 minutes. That is, we illustrate that nf-XCT as a inspection method is highly competitive to conventional radiography or radioscopy. The presented work also reveals possibilities for other fields like microelectronics etc.
•Direct comparison between medical and microCT for industrial NDT.•Challenging test objects even for typical microCT up to 225 kV.•Accuracy of microCT demonstrated as expected for all four test cases.•Medical CT shows reasonable results in some applications.•Indicates feasibility of fast, cost effective scanning for macro features using medical scanning.
