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- Digital radiography (20) (entfernen)
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The quality of additively manufactured (AM) parts is determined by the applied process parameters used and the properties of the feedstock powder. The influence of inner gas pores in feedstock particles on the final AM product is a phenomenon which is difficult to investigate since very few non-destructive measurement techniques are accurate enough to resolve the micropores.
3D X-ray computed tomography (XCT) is increasingly applied during the process chain of AM parts as a non-destructive monitoring and quality control tool and it is able to detect most of the pores.
However, XCT is time-consuming and limited to small amounts of feedstock powder, typically a few milligrams. The aim of the presented approach is to investigate digital radiography of AM feedstock particles as a simple and fast quality check with high throughput. 2D digital radiographs were simulated in order to predict the visibility of pores inside metallic particles for different pore and particle diameters. An experimental validation was performed. It was demonstrated numerically and experimentally that typical gas pores above a certain size (here: 3 to 4.4 µm for the selected X-ray setup), which could be found in metallic microparticles, were reliably detected by digital radiography.
Classical film radiography is a well-established NDT technique and it is most commonly used for testing weld seams and corroded pipes e.g. in oil and gas industry or in nuclear power plants. In the course of digitization, digital detector arrays (DDA) are finding their way into industrial applications and are replacing film radiography step by step. This study deals with the latest generation of DDAs, the photon counting and energy resolving detectors (PCD), and their characteristics compared to charge integrating detectors (CID). No matter which technology to use, radiography still lacks a general issue: A three-dimensional object is projected onto a two dimensional image. Of course, advanced computed tomography (CT) algorithms exist since many years, but if the object to investigate is too large to fit into the manipulation system or its shape is not appropriate, CT is not feasible or sensible to be applied. To overcome this limitation, numerous laminographic algorithms have been developed in the past. In this study, photon counting detectors are used in combination with co-planar translational laminography to gain reconstructed three-dimensional volumes. Both laminographic testing and PCDs require a serious knowledge of many parameters that can influence the image quality in the resulting datasets. These are e.g. the detector efficiency and calibration procedure, setting of energy thresholds, exposure data, number of projections, beam length correction and spatial resolution. The use of PCDs yields more variables to be considered compared to CIDs. The most important parameters in laminographic testing and in the use of PCDs are described in this study and limits are discussed.
Carbon fiber reinforced polymer ropes are gaining in significance in the fields of civil engineering and hoisting applications. Thus, methods of non-destructive testing (NDT) need to be developed and evaluated with respect to new challenges and types of defects. Particularly important is the development of in-service testing solutions which allow the integration in global online monitoring systems. Conventional methods like electrical resistivity or strain measurements using optical fibers are already in use. This study investigates the possibility of using various X-ray techniques to increase the reliability and significance of NDT and their applicability to in-service testing. Conventional film radiography is the most common technique; however, even after image enhancement of the digitized film, this technique lacks contrast sensitivity and dynamic range compared to digital detector array (DDA) radiography. The DDA radiography is a highly sensitive method; yet, the limitation is that it delivers 2D images of 3D objects. By the use of co-planar translational laminography the detectability of planar defects is superior to 2D methods due to multiple projection angles. Apart from this, it can be used on-site due to a rather simple setup and robust equipment. In this work two photon counting detectors (PCD) with different sensor materials (Si and CdTe) were used. The results show that the resolution and defect recognition is lower in case of DDA radiography and laminography using PCDs compared to high-resolution computed tomography. However, the DDA radiography and laminography are sensitive enough to both fiber breakage and delaminations and can be significantly advantageous in terms of measurement time and adaptability for on-site monitoring.
Similar to the success story of digital photography a major upheaval has been observed in digital industrial radiology. This paper is split into 3 parts:
Part 1: Film Replacement and Backscatter Imaging: Computed radiography with phosphor imaging plates substitutes film applications. 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. Photon counting and energy discriminating detectors are applied up to 300 Kv provide increased thickness dynamic and material discrimination by synchronously acquisition of images of the high and low energy part of the spectrum. 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 with newly designed back scatter cameras. Numeric modeling is used to design X-Ray optics and inspection scenarios as well as conducting RT training.
Part 2: Computed tomography (CT)
Part 3: Micro Radiography and Micro CT.
This work presents an investigation of the accuracy of a radiographic simulation model applied to subsea pipeline inspections. Experimental measurements of a sample in a water tank are used to develop a set of calibrated simulation parameters for the modelling software aRTist. Image quality parameters such as signal-tonoise ratio, contrast and basic spatial resolution are compared with the aim of matching simulated values to experimental results. With this method signal-to-noise ratio was successfully matched while differences were still found in contrast-to-noise ratio comparisons. This means that measurements depending on absolute intensity are not accurate enough, however wall thickness measurements in tangential images, which are not based on absolute intensity, were found to produce similar results in simulated and experimental cases. The differences in contrast and intensity are thought to be due to detector backscatter and additional scatter from out-of-setup objects within the exposure bay, due to a lack of source collimation. These would affect the experimental results but were not included in the simulated setup. This was investigated by including different proportions of peripheral water and other objects in the modelled setup and examining the effect on Image quality parameters. Results show that this additional scatter has a significant impact on the radiograph, particularly on image contrast, and is therefore the likely cause of differences between experimental and simulated images. This implies that it will be very difficult to completely match simulated to experimental results, as including all possible scattering objects in the model would be very complex. An improvement could be made by using real subsea data to estimate this additional scattering, which could then be used to calibrate the model. However there would still be significant uncertainty in the ability of the model to accurately produce realistic intensity and contrast.
In order to enhance the supply chain security at airports, the German federal ministry of education and research has initiated the project ESECLOG (enhanced security in the air cargo chain) which has the goal to improve the threat detection accuracy using one-sided access methods. In this paper, we present a new X-ray backscatter technology for non-intrusive imaging of suspicious objects (mainly low-Z explosives) in luggage's and parcels with only a single-sided access. A key element in this technology is the X-ray backscatter camera embedded with a special twisted-slit collimator. The developed technology has efficiently resolved the problem related to the imaging of complex interior of the object by fixing source and object positions and changing only the scanning direction of the X-ray backscatter camera. Experiments were carried out on luggages and parcels packed with mock-up dangerous materials including liquid and solid explosive simulants. In addition, the quality of the X-ray backscatter image was enhanced by employing high-resolution digital detector arrays. Experimental results are discussed and the efficiency of the present technique to detect suspicious objects in luggages and parcels is demonstrated. At the end, important applications of the proposed backscatter imaging technology to the aviation security are presented.
Radiologic evaluation techniques are nondestructive testing (NDT) used to detect the bulk of explosives and contraband materials in large objects. As compared to conventional low-energy (<450 key) X-ray imaging, high-energy (>1 MeV) digital X-ray radiography is required for the NOT of large containers because of the need for high penetration through thick materials, sensitivity, and the ability to distinguish between low-and high-Z materials. Mobile, high-energy, and high-resolution radiologic techniques are useful to detect contraband and threat materials in digital radiographic images of containers with complex packing. This paper presents a mobile, high-energy X-ray radiographic technique for the in-field nondestructive inspection of cargo containers. The developed experimental technique consisted of a betatron as a high-energy (7.5 MeV) X-ray source and a high-resolution (400 mu m) matrix detector for the digital X-ray imaging. In order to evaluate the detection efficiency and image quality of the measurement technique, a test specimen was proposed that was made of a 3 mm thick steel container with an inner dimension of 60 x 30 x 40 cm(3) comprising different low-and high-Z materials. Image quality indicators were used to assess the essential image quality parameters such as image basic spatial resolution, effective attenuation coefficient, and signal-to-noise ratio (SNR). Experimental investigations were performed on a 6.1 m sea freight container with mockup dangerous materials in complex packing. Preliminary experimental results showed that the proposed technique was able to distinguish between liquids and solids, as well as detect contraband materials. Furthermore, a remarkable SNR of 400 was achieved in the measured digital X-ray images. The influence of temperature on X-ray radiation dose rate at different X-ray energies was also investigated. Finally, important applications of the proposed technique in the context of maritime security are discussed.
This paper presents a new X-ray backscatter technique (XBT) for non-destructive imaging of aerospace materials with only a single-sided access. It uses a special twisted slit collimator to inspect the whole object by changing the viewing direction of the X-ray backscatter camera. For the first time, the X-ray backscatter measurements were conducted using high-energy (>500 keV) X-ray sources. Experiments were performed on thick complex structured aluminium components, stringers and honeycomb structures to validate the applicability of the present technique to image small changes in the material properties and also to detect low-density material inclusions. In order to reduce the inspection time from hours to several seconds and to improve the image quality of the X-ray backscatter image, the backscattered signals were measured using a digital detector array with high spatial resolution (200 µm). The influence of the energy of the X-ray source and the slit width of the camera on the X-ray backscatter image were also investigated. In the proposed technique, the whole object is irradiated by an un-collimated X-ray beam resulting in a low image acquisition time of 3 min that facilitates the use of XBT for the real time NDT&E of aerospace materials.
In this contribution, we present a dual high-energy X-ray imaging technique for cargo container inspection using the 'spectral high-energy X-ray attenuation method'. This method is based on attenuation of continuous highenergy spectra. The developed experimental technique consists of a betatron as high-energy (up to 7.5 MeV) X-ray source and a matrix detector with high spatial resolution (400 ìm) for digital X-ray imaging. In order to evaluate the material discrimination capability using dual high-energy X-ray imaging, a test specimen is proposed, comprising step wedges of different low and high atomic number (Z) materials. The selected X-ray spectra for the dual-energy experiments correspond to 3 MV and 7.5 MV acceleration potential of the betatron. We evaluated the ratio between low- and high-energy X-ray attenuation coefficients quantitatively based on simulated poly-energetic high-energy X-ray source spectra and the detector sensitivity using the 'analytical Radiographic Testing inspection simulation tool' (aRTist) developed at BAM. The simulated effective attenuation coefficients are compared with corresponding experimental results in order to establish a method for identification of low- and high-Z materials in the container. Finally, important applications of the proposed technique in the context of aviation security are discussed.