Contrast-based notch-to-crack transfer function for digital radiography

Digital detector arrays (DDAs) have developed rapidly in some segments of the industry as a replacement for film radiography or in some cases computed radiography, especially in the aeronautical industry and for casting inspections. However, these detectors show limits when applied for inspection of high thicknesses of steel or other absorbing materials, linked to high levels of noise and scattered radiation. New technologies in the form of photon counting detectors (PCDs) are being developed for some specific inspections where usual DDAs are not proving effective enough. These detectors allow the choice of an energy threshold under which the X or gamma photons are not being considered when creating the digital image, allowing the user to basically cut off part of the scattered radiation from the signal received by the detector, hence improving the signal to noise ratio (SNR) and the image quality. Despite the drawback of a very small active area, such systems provide advantages over usual DDAs in specific settings such as: Inspection of high thicknesses; Inspections in environments where there is ambient radiation (nuclear power plants for example); Inspections where different materials need to be differentiated on the radiographic image (dual energy). This paper regards tests that have been performed jointly by CETIM and INTERCONTROLE agents at the request of CETIM and using a PCD developed by INTERCONTROLE especially to perform inspections using high-energy X or gamma sources. These tests were performed using X-ray generators of 450 and 530 kV, and their aim was to compare the performance of PCDs relative to standard DDAs on high thicknesses of steel blocks and samples. Similar exposures were made using the PCD and a DDA for steel thicknesses of 50 to 90 mm (see figure 1), and the comparison are based on measures of image quality index on wire-type image quality indicators (IQIs, see figure 2), signal to noise ratio, spatial resolution (SRb) and contrast to noise ratio (CNR) on the different images.

The Westinghouse Marine division has been using a high power laser (15 kW) for production cutting of mild steel and stainless steel parts for almost two years. The low carbon steel plates have a thickness range of 0.64 to 4.78 centimeters. The 300 and 400 series stainless steel plates have a thickness range of 0.64 to 1.91 centimeters. Data plots using process parameters of power, speed, thickness, and energy per unit length (kJ/CM) have the same general shape and behavior as laser weld data. There appears to be a continous shift in process mechanics from “laser cutting using gas assist” for thin sheets to “gas cutting using laser assist” for the thick plates. A ratio of mild steel cutting to welding (units of energy/unit length) indicates a factor of ten increase in energy assist using Oxygen. A similiar ratio of cutting to welding for stainless steel indicates a factor of three assist for thin sheet but this drops to a factor of 0.5 for laser cutting of thick stainless steel plate. In the larger view, Oxygen is not a source of energy in cutting stainless steels.

A series of simulated cracks in 301 stainless steel (SS), consisting of slits with depths from 12.8% to 40% of the plate thickness, is fabricated in this study. The examination includes a microfocus X-ray tube and a digital detector array (DDA) with 0.075 mm pixels at three angles of incidence (0°, 5° and 10°). The basis of the methodology for the minimum detectable slit width stems from the noise statistics in the images and a minimum detectable contrast-to-noise ratio (CNR) of 3. These minimum detectable widths range from 0.019 mm to 0.003 mm for 12.8%-deep and 40.0%-deep slits, respectively, for the 0° incidence condition. As the incident angle increases to 10°, the size of the minimum detectable slit width also increases, up to a factor of two for the shallower slits. It is noted that these simulated cracks, which have straight parallel sides and flat bottoms, do not accurately represent natural cracks that have irregular paths and taper at depth. Therefore, the results in this study represent the best scenario for detection, establishing some bounds of crack width detectability.

For the safety and airworthiness of aircraft, the aerospace industry has stringent product quality requirements to ensure structural integrity of critical components. Non-destructive inspections (NDI) are routinely performed to ensure product quality and identify defects before they reach critical size. Radiographic inspection plays a key role for inspection of aircraft structural components. Film-based radiography requires consumables, darkroom facility, and manual processing; this is not only time consuming, but also requires more radiation exposure than digital systems. Digital radiography eliminates these requirements and currently in a transition state of switching to two kinds of digital technologies: (1) Digital Detector Arrays, DDA, also known as flat panel detectors, digital radiography, DR, and (2) Computed Radiography, (CR). Flat panel detector (DDA) based allows faster/easier straight acquisition of the radiographic image digitally without the necessity of films or even phosphorous plate like in CR. DR/DDA is also suitable for real time imaging and automation. Before implementing this technology as aircraft inspection procedures, a detailed performance assessment leading to inspection qualification is required. This paper highlights the initial and periodic performance evaluation metrics necessary during initial performance evaluation and periodic maintenance.

The purpose of this article is to numerically quantify the stress state of complex loaded thick steel plates using the fundamental theory of acoustoelasticity, which is the relationship with stress and ultrasonic velocity in the nonlinear regime. The normal and shear stresses of a thick plate can be measured using a phased array placement of ultrasonic sensors and Rayleigh ultrasonic waves. Three measurement angles (i.e., 0 45 and 90 degrees) are selected since three measurements are needed to solve the stress tensor in an isotropic plate. The ultrasonic data is influenced significantly by the frequency of the Rayleigh waves as well as the thickness of the plate being examined; consequently the overall experimental process is influenced by the measurement parameters. In this study, a numerical demonstration is implemented to extract the nonlinearity coefficients using a 3D structural geometry and Murnaghan material model capable of examining the effects of various plate thicknesses and ultrasonic frequencies on the shear stress measurement. The purpose is that as the thickness becomes smaller, the shear stress becomes negligible at the angled measurement. For thicker cross section, shear stress becomes influential if the depth of penetration of Rayleigh wave is greater than the half of the thickness. The correlation between the depth of penetration and shear stress is then obtained. The numerical results are compared with 1 MHz ultrasonic frequency and a 3/8 inch thick steel plate loaded uniaxially while the measurement direction is angled to have the presence of shear stress in the measurement direction.

Revealing the failure mechanism of industrial Fe-25Cr-20Ni stainless steel plate: Fine-grained segregation band and brittle phase induced delamination cracking

The thickness of steel plates used for large structures has been increasing with the rapid increase in the size of welding structures. The growing capacity of large-scale ships, such as container ships, has led to an increase in the thickness and strength of steel plates for shipbuilding. The steel plate toughness and resistance to brittle fractures tend to decrease for thick plates because of the so-called thickness effect. This study uses 80-mm-thick steel plates and two welding processes (i.e., flux cored arc welding process and electron gas welding process) to produce full-thickness weld joints. The welding residual stress in both welded joints is measured to evaluate the brittle crack propagation path. This study aims to investigate the effect of welding variables on the crack arrest toughness and crack propagation path of thick steel-plate welds. The thick steel plate has a high possibility in brittle fracture. A quantitative analysis is conducted through a temperature-gradient ESSO test to clarify the effect of the welding variables on the flux cored arc welding and electron gas welding process joints of steel plates with 50 and 80 mm thicknesses. The welding residual stress is also measured to evaluate the welding residual stress effect in both welding processes on the brittle crack propagation path using a neutron science analysis.

Background: Stainless steel and titanium are two different metals with different mechanical and metallurgical properties. Stainless steel is twice more stiffer than titanium. Internal fixation of fractures with stainless steel plates is likely to produce more rigid fixation than titanium plates. Hence, stainless steel plate fixation is likely to produce healing of fracture site with minimum callus/primary healing. This study analyzes whether these properties of the metals influence the healing of the fractures and their outcomes. Materials and Methods: Thirty-five cases of fractures of radius and ulna were treated by internal fixation using stainless steel limited contact-dynamic compression plate (LC-DCP) (Group I) in 17 patients and titanium LC-DCP (Group II) in 18 patients. Follow-up was done at 6 weeks, 12 weeks, 6 months, and 1 year for clinical and radiological healing and complications. Results: All the fractures united in time. 10 (62.5%) patients in Group I and 9 (56.2%) patients in Group II showed primary union and 6 (37.5%) patients in Group I and 7 (43.2%) patients in Group II showed union with callus formation. No complications were observed. Conclusion: Stainless steel and titanium are two different metals with different mechanical and metallurgical properties. However, fixation of fractures with these metals failed to show the difference in the patterns of fracture healing.

Catalytic wall reactor: Catalytic coatings of stainless steel by VO x/TiO 2 and Co/SiO 2 catalysts

To solve the problem of collapses caused by local buckling of steel plates under compression in traditional steel towers, a novel steel-concrete-steel (SCS) sandwich composite tower for a wind turbine is proposed in this paper. To study the buckling behaviour of steel plates in SCS sandwich composite towers, six specimens were designed and tested under axial compression. The specimens were designed considering the key parameters of curvature radius, thickness of the steel plate, and the spacing-to-thickness ratio (the ratio of stud spacing to the thickness of steel plate). The failure modes, normalised average stress-strain curves and load-strain curves of the specimens were assessed, and the effects of the curvature radius and the spacing-to-thickness ratio of the steel plate were analysed. The experimental results showed that the buckling strength of the steel plate increased with a decrease in the ratio of the curvature radius to the thickness of the steel plate. The finite element (FE) model of the elastic buckling stress of the steel plate of the SCS sandwich composite tower was employed and validated against the test results. In parametric study, the effects of governing parameters including the curvature radius of the steel plate, thickness of the steel plate and spacing of the studs, on the effective length factors of the inner and outer steel plates were analysed. Subsequently, the design rules of the effective length factor of the inner and outer steel plates, and the design methods of spacing of studs to prevent local instability of the inner and outer steel plates before yielding were proposed.

With the increase of service life and the change of current codes, most historical wood buildings do not meet the structural requirements and urgently need reinforcement and protection. In order to find out the strengthening effect of wood beams strengthened with steel plates in historical buildings. Firstly, based on the theoretical analysis, the calculation formulas of ultimate flexural capacity of wood beams are proposed. Then, the ultimate flexural capacity calculation results and finite element simulation analysis results of rectangular wood beams strengthened with bonded steel plates on both sides, rectangular wood beams strengthened with embedded steel plates and circular wood beams strengthened with embedded steel plates are compared and studied. The results show that the calculation results of the theoretical formulas are consistent with the results of the finite element simulation analysis. When common 4 ~ 10 mm thick steel plates are bonded on both sides to strengthen rectangular wood beams, the ultimate flexural capacity of wood beams is improved by 98.65 % ~ 247.05 %. When common 4~10 mm thick steel plates are embedded to strengthen rectangular wood beams, the ultimate flexural capacity of wood beams is improved by 49.27 % ~ 123.44 %. When common 4 ~ 10 mm thick steel plates are embedded to strengthen circular wood beams, the ultimate flexural capacity of wood beams is improved by 41.83 % ~104.82~. The research results can provide calculation basis and theoretical basis for the protection of wood beams in historical buildings.

In recent years, studies on magnetospheric plasmas have increased drastically. Different theoretical models are proposed to match the data observed from various space missions. Still, no sufficient experimental setup is there to replicate the formation like a double layer in these kinds of plasma. In this study, we have made an experimental setup that nearly replicates the magnetospheric plasma environment. We have placed a stainless steel (SS) plate inside our plasma chamber. The argon plasma is produced in the hot cathode discharge method at comparatively high pressure. Then a positive bias is applied to the SS plate with and without attaching a permanent magnet. This positively biased SS plate creates a fireball and firerod-like structures in the absence and presence of the magnet, respectively. This scenario is analogous to the Earth’s magnetospheric plasma and the SS plate represents the pole of the Earth. In this plasma, we have studied the axial variation of ion density (ni ), electron temperature (Te ), electron energy distribution function (EEDF), and the plasma potential for both cases. Lastly, we have discussed the nature of the plasma potential variation with a theoretical model.

Photoconductive polycrystalline mercuric iodide deposited on flat panel thin film transistor (TFT) arrays is one of the best candidates for direct digital X-ray detectors for radiographic and fluoroscopic medical imaging. The mercuric iodide is vacuum deposited by Physical Vapor Deposition (PVD). This deposition technology has been scaled up to the 20cmX25cm size required in common medical imaging applications. A TFT array with a pixel pitch of 127 microns is used for these imagers. In addition to successful imager scale up, non-TFT based detectors were developed in order to improve analysis methods of the mercuric iodide photoconductor itself. These substrates consist of an array of palladium or ITO stripes on a glass substrate. Following deposit of the photoconductor, striped bias electrodes are deposited on top of the photoconductor at a 90 degree orientation to the bottom electrodes. These substrates provide more information than was previously available on the dark current and signal uniformity of the mercuric iodide photoconductor without the use of expensive TFT arrays. Mercuric iodide photoconductor thicknesses between 110 microns and 300 microns were tested with beam energy between 40 kVp and 120 kVp utilizing exposure ranges typical for both fluoroscopic and radiographic imaging. Diagnostic quality radiographic and fluoroscopic images at up to 15 pulses per second were demonstrated. Resolution tests on resolution target phantoms were performed and performance close to the theoretical sinc function up to the Nyquist frequency of ~3.9 lp/mm is shown (127 micron pixel pitch).

The modelling of peatland functioning, in particular the impact of anthropogenic warming and direct human disturbance on CO2, CH4 and N2O, requires detailed knowledge of the peat structure and of both water and gas flow with respect to the groundwater table level. To this end, freezing is nowadays increasingly used to obtain small size peat samples for X-ray micro computed tomography (X-ray μ-CT) as required by the need to increase the resolution of the 3D X-ray CT images of the peat structure recorded. The aim of this study was to analyze the structure of a peat material before and after freezing using X-ray μ-CT and to look for possible alterations in the structure by investigating looking at the air-filled porosity. A highly decomposed peat material close to water saturation was selected for study and collected between 25 and 40 cm depth. Two samples 4 × 4 × 7 cm3 in volume were analyzed before and after freezing using an X-ray μ-CT Nanotom 180NF (GE Phoenix X-ray, Wunstorf, Germany) with a 180 kV nanofocus X-ray tube and a digital detector array (2304 × 1152 pixels Hamamatsu detector). Results showed that the continuity and cross section of the air-filled tubular pores several hundreds to about one thousand micrometers in diameter were altered after freezing. Many much smaller air-filled pores not detected before freezing were also recorded after freezing with 470 and 474 pores higher than one voxel in volume (60 × 60 × 60 μm3 in volume each) before freezing, and 4792 and 4371 air-filled pores higher than one voxel in volume after freezing for the two samples studied. Detailed analysis showed that this increase resulted from a difference in the whole range of pore size studied and particularly from a dramatic increase in the number of air-filled pores ranging between 1 voxel (216 103 μm3) and 50 voxels (10.8 106 μm3) in volume. Theoretical calculation of the consequences of the increase in the specific volume of water by 8.7 % when it turns from liquid to solid because of freezing led to the creation of a pore volume in the organic matrix which remains saturated by water when returning to room temperature and consequently to the desaturation of the largest pores of the organic matrix as well as the finest tubular pores which were water-filled before freezing. These new air-filled pores are those measured after freezing using X-ray μ-CT and their volume is consistent with the one calculated theoretically. They correspond to small air-filled ovoid pores several voxels in volume to several dozen voxels in volume and to discontinuous air-filled fine tubular pores which were both detected after freezing. Finally, the increase in the specific volume of water because of freezing appears also be also responsible for the alteration of the already air-filled tubular pores before freezing as shown by the 3D binary images and the pore volume distribution.

A new X-ray backscatter imaging technique for non-destructive testing of aerospace materials