Case Studies in Nondestructive Testing and Evaluation最新文献

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.

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 intergranular corrosion depth showed by root cause failure analysis is smaller than that showed by EC inspection. We attribute the EC inspection results deviation to a tube magnetisation due to mechanical stress and to a secondary phase due to an incomplete solubilisation after tube conforming and welding.

Traditionally, these tubes are visually inspected and deemed acceptable but our conclusions reveal that eddy current testing is capable of detecting some corrosion anomalies which makes the tubes unfit for service.

Speed is an important parameter of an inspection system. Inline computed tomography systems exist but are generally expensive. Moreover, their throughput is limited by the speed of the reconstruction algorithm. In this work, we propose a Neural Network-based Hilbert transform Filtered Backprojection (NN-hFBP) method to reconstruct objects in an inline scanning environment in a fast and accurate way. Experiments based on apple X-ray scans show that the NN-hFBP method allows to reconstruct images with a substantially better tradeoff between image quality and reconstruction time.

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.

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.

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.

In this work a test artifact containing cylindrical elements with diameters in the range typically used in lightweight cellular structures is used to investigate the influence of features' size and printing orientation on the porosity and shape deviation of each feature. In order to assess the reproducibility of the process, several replicas of the test object are produced in polyamide-12 (PA12) using the same LS process conditions. An X-ray Computed Tomography (CT)-based quality control approach, which uses both image processing of CT-slices and porosity analysis (porosity content, pores count and pores volume distributions) is used to gather the information.

Insulation boards made out of larch bark were pressed and scanned with an industrial X-ray computed tomograph (CT) in order to study the structure of the boards and to allow structure-based thermal modeling. The CT images were segmented using a categorization algorithm based on ANOVA. Apart from gaining knowledge about panel porosity, understanding of the inhomogeneous bark boards was enhanced by finding that two main components are prevalent. That knowledge of the board's inner microstructure enabled the application of a numerical model for thermal conductivity based on the finite difference method (FDM). Contrary to simple cut-ups, the application of CT and subsequent modeling enables the evaluation of the effects of particle orientation on a panel's thermal conductivity. Panels with horizontal particles (oriented parallel to the panel plane) proved to have a significantly lower thermal conductivity than panels with vertical particles (oriented orthogonal to the panel plane). This trend could be confirmed by means of the presented modeling approach, which allows further theoretical ex ante optimization in the production process. These findings give the direction for developments of efficient bark insulation panels with well-defined microstructure.

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).

However, the difficulty in selecting suitable scanning parameters and suitable surface determination settings, limits a better acceptance of CT as a CMS. Moreover, standard CT users are subject to the algorithms and boundary conditions implied by the use of commercial analysis software.

In this context, this paper is concerned with the experimental evaluation of the influence of surface determination process on multi-material measurements, using functions available in the commercial CT data analysis software Volume Graphics VGStudio Max 2.2.6.

Calibrated step gauges made of different materials, i.e. PEEK, PPS, and Al were used as reference standards. The step gauges were assembled in such a way as to have different multi-material X-ray absorption ratios. Comparative measurements of mono-material assemblies were performed as well. Different segmentation processes were considered (e.g. ISO-50%, local threshold, region growing, etc.), patch-based bidirectional length analyses were carried out to perform in-material measurements on the assemblies.

This work discusses the different approaches based on real CT scans, and aims to provide advice on the segmentation process for multi-material measurements.

This paper describes the development of different novel antenna concepts for improving the spatial resolution of microwave based non-destructive testing (NDT) at 24 GHz. In a great number of applications the antenna of the sensor can be brought very close to the device under test. In these cases, the near field characteristics of the antennas are crucial for a high resolution. However, common sensor heads offer either a high image resolution or a high penetration depth. In order to combine both of the characteristics different antenna concepts have been developed. The objectives were to obtain a high return loss combined with a sufficient high dynamic range and a near field focusing of electromagnetic waves in order to yield a high resolution. Altogether, three antennas have been set up. Each antenna has been calculated analytically, followed by a FEM simulation, near field measurements and an experimental verification.

We compare the quality of reconstruction obtainable using various laminographic system trajectories that have been described in the literature, with reference to detecting defects in composite materials in engineering. We start by describing a laminar phantom representing a simplified model of composite panel, which models certain defects that may arise in such materials, such as voids, resin rich areas, and delamination, and additionally features both blind and through holes along multiple axes. We simulate ideal cone-beam projections of this phantom with the different laminographic trajectories, applying both Simultaneous Iterative Reconstruction Technique (SIRT) and Conjugate Gradient Least Squares (CGLS) reconstruction algorithms. We compare the quality of the reconstructions with a view towards optimising the scan parameters for defect detectability in composite NDT applications.