Case Studies in Nondestructive Testing and Evaluation最新文献

Railway wheelsets consist of three main components; the wheel, axle and axle bearing. Faults can develop on any of the aforementioned components, but the most common are related to wheel and axle bearing damages. The continuous increase in train operating speeds means that failure of an axle bearing can lead to very serious derailments, potentially causing human casualties, severe disruption in the operation of the network, damage to the tracks, unnecessary costs, and loss of confidence in rail transport by the general public. The rail industry has focused on the improvement of maintenance and online condition monitoring of rolling stock to reduce the probability of failure as much as possible. This paper discusses the results of onboard acoustic emission measurements carried out on freight wagons with artificially damaged axle bearings in Long Marston, UK. Acoustic emission signal envelope analysis has been applied as a means of effective tool to detect and evaluate the damage in the bearings considered in this study. From the results obtained it is safe to conclude that acoustic emission signal envelope analysis has the capability of detecting and evaluating faulty axle bearings along with their characteristic defect frequencies in the real-world conditions.

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.

Additive manufacturing (AM) allows for fast fabrication of three dimensional objects with the use of considerably less resources, less energy consumption and shorter supply chain than would be the case in traditional manufacturing. AM has gained significance due to its cost effective method which boasts the ability to produce components with a previously unachievable level of geometric complexity in prototyping and end user industrial applications, such as aerospace, automotive and medical industries. However these processes currently lack reproducibility and repeatability with some ‘prints’ having a high probability of requiring rework or even scrapping due to out of specification or high porosity levels, leading to failure due to structural stresses. It is therefore imperative that robust quality systems be implemented such that the waste level of these processes can be significantly decreased. This study presents an artefact that is optimised for characterisation of form using computed tomography (CT) with representative geometric dimensioning and tolerancing features and internal channels and structures comparable to cooling channels in heat exchangers. Furthermore the optimisation of the CT acquisition conditions for this artefact are presented in light of feature dimensions and form analysis. This paper investigates the accuracy and capability of CT measurements compared with reference measurements from coordinate measuring machine (CMM), as well as focus on the evaluation of different AM methods.

Internal defects such as voids and porosity directly influence mechanical properties, durability, service life and other characteristics of industrial parts. There are several non-destructive and destructive methods for defects detection and evaluation. Recently, X-ray Computed Tomography (CT) has emerged as an effective tool for geometrical characterization of internal defects. 3D information about internal voids/porosity extracted from CT datasets can be utilized in many applications, such as production processes optimization and quality control. However, there are still challenges in using CT as a traceable method for internal voids dimensional measurements. In order to enhance the accuracy and reliability of CT porosity measurements, a metrological validation method is required.

This study presents the application of a new reference object for accuracy evaluation of CT porosity measurements and discusses results obtained by using it. The reference object is made of aluminium and is composed of a cylindrical body and four cylindrical inserts with micro-milled hemispherical features of calibrated sizes resembling artificial flaws. The accuracy of porosity measurements is evaluated according to various characteristics (diameters and depths measurements errors) and repeatability of measurements. Design of experiments technique is used to investigate the influence of CT parameters settings on porosity measurement accuracy.

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.

Industrial X-ray computed tomography (CT) is an emerging laboratory-based non-destructive testing technique used in a variety of applications for samples ranging from 1 mm to usually 300 mm in diameter. Usually, microCT scanners are used for industrial non-destructive testing due to the superior resolution possible compared to medical CT scanners, but it is not generally known that medical CT scanners can produce reasonable results when high resolution is not needed. As demonstrated in this case study of very dense objects, far shorter scan time is required, compared to conventional laboratory industrial CT systems, consequently being a better solution for applications such as quick scout-scans, high throughput applications and larger objects. This case study makes use of four typical industrial test objects, specifically chosen as candidates which would be expected to be too dense for relatively low-voltage medical scanners. The respective test objects were scanned with both medical and microCT scanners and the results compared for the purpose of industrial non-destructive analysis. The test objects are a steel turbine blade, a titanium casting, a concrete cylinder with aggregate stones and porosity, and a concrete block with metal fiber reinforcement.

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.

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.

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.