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- Ray tracing (5)
- Austenitic weld (3)
- Simulation (3)
- Anisotropy (2)
- Container inspection (2)
- High-energy X-ray imaging (2)
- Monte Carlo methods (2)
- SAFT (2)
- Ultrasonic sound field (2)
- 3D ray tracing (1)
In this contribution a 3D ray tracing model for ultrasonic
field evaluation in inhomogeneous anisotropic materials
such as austenitic welds is presented. The inhomogenity of
austenitic weld material is represented as several
homogeneous layers. The general problem of energy
reflection and transmission at the boundaries of the layers
are solved resulting 3D amplitude and energy reflection and
transmission coefficients. The directivity factor for the ray in
general arbitrary oriented austenitic weld material (including
lay back orientation) is determined based on Lambs
reciprocity theorem. The transducer excited ultrasonic fields
are accurately evaluated by employing ray directivity factor,
transmission coefficients, divergence of the ray bundle and
density of rays. Finally, the comparison between theoretical
and experimental results will be described.
Ultrasonic examination of anisotropic inhomogeneous austenitic welds is challenging, because of the columnar grain structure of the weld leads to beam skewing and splitting. Modeling tools play an important role in understanding the ultrasound field propagation and optimization of experimental parameters during the ultrasonic testing of austenitic welds as well as the interpretation of the test results. In this contribution, an efficient theoretical model based on the ray tracing concepts is developed to calculate the ultrasonic fields in inhomogeneous austenitic welds quantitatively. The developed model determines the ultrasound fields by taking into account the directivity of the ray source, the inhomogenity of the weld as well as ray transmission coefficients. Directivity of the ray source in columnar grained austenitic materials (including layback orientation) is obtained in three dimensions based on Lamb's reciprocity theorem. Ray energy reflection and transmission coefficients at an interface between two general columnar grained austenitic materials are calculated in three dimensions. The ray tracing model predictions on inhomogeneous austenitic weld material are compared against those from CIVA, a commercial non-destructive modeling and simulation tool. The ultrasonic modeling tools in CIVA are based on semi-analytical solutions. For beam propagation simulation, a so-called 'pencil method' is used, which involves modeling the probe as a set of individual source points, each radiating 'a bundle' of diverging rays into the medium and integrating those elementary contributions. Inhomogenity in the weld region is approximated by mapping the grain orientations on weld macrograph. Simulation results for ultrasonic field profiles for an austenitic weld are shown to be in good agreement with the corresponding experimental results.
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.
In this contribution a simulation tool is developed to compute the energy skewing angles and energy coefficients
for the reflected and refracted plane waves in following general cases: (1) reflection and refraction
of plane elastic waves at an interface between isotropic and transversely isotropic solid, (2) reflection
and refraction of plane elastic waves at an interface between transversely isotropic and isotropic solid, (3)
reflection and refraction of plane elastic waves at an interface between two general transversely isotropic
solid and (4) reflection of plane elastic waves from a stress free boundary of a transversely isotropic solid.
Computational results for analytically evaluated acoustic wave energy skewing angles and energy reflection
and transmission coefficients in acoustically anisotropic materials such as austenitic steel materials
exhibiting columnar grain orientation are presented. The obtained results show that the acoustic energy
skewing angles and coefficients in austenitic steel materials strongly depend upon the columnar grain
orientation and are less influenced by the grain orientations which are parallel and perpendicular to the
interface.
This contribution describes a computationally efficient ray tracing algorithm for evaluating transducer generated ultrasonic wave fields in anisotropic materials such as austenitic cladded and austenitic weld components. According to this algorithm, ray paths are traced during its propagation through various layers of the material and at each Interface the problem of reflection and transmission is solved. The presented algorithm evaluates the transducer generated ultrasonic fields accurately by taking in to account the directivity, divergence, density of rays, phase relations as well as transmission coefficients. The ray tracing algorithm is able to calculate the ultrasonic wave fields generated by a point source as well as a finite dimension transducer. The simulation results are compared quantitatively with the results obtained from Elastodynamic Finite Integration Technique (EFIT) on several configurations generally occuring in the ultrasonic non destructive testing of anisotropic materials. The excellent agreement between both models confirms the validity of the presented ray tracing algorithm. Finally, the ray tracing model results are also validated by means of experiments.
In the context of the German aviation security research and development project SILUFRA (secure air freight transport chains), BAM has developed a high-resolution and high-energy X-ray imaging technology for the reliable detection of dangerous and illicit materials in densely packed air freight containers. In the developed technology, a novel combination of high-energy (2-7.5 MeV) X-ray betatron as the radiation source and a high-resolution digital detector array (DDA) for the X-ray imaging was utilized to improve the probability of detecting contraband and explosive materials by enhancing the spatial and contrast resolution in the digital X-ray image. In addition, flexible rotations of the high-energy X-ray source and the digital detector array can lead to clarify the suspicious region of interest (ROI) in air freight containers efficiently. Thus, reduces the false alarm rates and the need for expensive manual inspections of the whole container load. In order to evaluate the detection efficiency, we carried out the experimental investigations on a real air freight container loaded with typical cargo materials such as heavy automobile components and electronic products as well as mock-up dangerous and contraband materials. Furthermore, the material discrimination in the radiographic images was evaluated based on the dual high-energy X-ray imaging method. Finally, important applications of the proposed imaging technology to the air cargo security are discussed
For the radiographic investigation of large cargo Containers the energies of conventional Xray tubes are inadequately for certain layer thicknesses. In that case the high energy radiation sources like electron accelerators and gamma radiators (60CO) are adequate for the non invasive inspection of large Containers because of the high penetration through thick materials. Multiple imaging even enables to distinguish between different materials. The main challenging task in air and sea cargo Container inspection is to improve the detectability of contraband and dangerous materials which are hidden in the heterogeneously packed Containers by detailed analysis of cluttered radiographic images. So it is to be expected that objects of organic substances like certain explosives or their precursors are hard to identify behind thick walls of heavy metal objects such as engine-blocks with flat bottom holes. The primary aim here is to investigate the detectability of dangerous materials (typically of light elements) in cargo Containers using high energy X-ray digital radiography.
The synthetic aperture focusing technique (SAFT) is an imaging technique commonly used in ultrasonic inspection. In order to apply SAFT to the inspection of austenitic welds, the inhomogeneous anisotropic nature of the weld structure has to be taken into account. A suitable approach to accomplish this, is to couple the SAFT-algorithm with a ray tracing program (RT-SAFT). While SAFT-imaging of cracks in austenitic welds by use of ray tracing has been carried out before, all attempts so far were limited to longitudinal cracks which usually allows a treatment as 2-dimensional problem. In case of transverse cracks, a full 3-dimensional ray tracing is necessary in order to perform a SAFT-reconstruction. In this paper, we give an outline of our attempts to reconstruct images of transverse cracks in austenitic welds, utilizing 3-dimensional ray tracing and a layered structure model derived from an empirical model of grain orientations in welds. We present results of this RT-SAFT on experimental data taken from transverse cracks in different austenitic welds, which show that size and position of the cracks can be estimated with good accuracy, and compare them to images obtained by assuming an isotropic homogeneous medium which corresponds to the application of the classical SAFT-algorithm.
In this contribution, we discuss the influence of scattered radiation on materials’ effective attenuation coefficients at higher X-ray energies. The selected X-ray spectra for the dual-energy experiments correspond to 3 MV and 7.5 MV acceleration potential of the used betatron. Experiments were performed on a test phantom containing step wedges of different low- and high-Z materials. 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. Furthermore, the influence of scattered radiation is evaluated using an efficient Monte-Carlo simulation. The simulation results are compared quantitatively with experimental investigations. Finally, important applications of the proposed technique in the context of aviation security are discussed.
The research and development (R&D) in the field of safety and security of sea-freight Containers has gained more importance after the U.S. house resolution 1 (H.R.1). According to this law, all the freight Containers which are transported from non-U.S. port of origin to U.S. ports should be inspected 100% against explosive and contraband materials using non-intrusive imaging equipment and radiation detectors. As the port of Hamburg and Bremerhaven are the leading Container ports in Europe, it is essential to develop reliable and high-resolution detection technologies for the non-destructive inspection of large sea-freight Containers.