Joseph N. Gray

A simulation-based design paradigm for complex cast components

This paper describes and exercises a new design paradigm for cast components. The methodology integrates foundry process simulation, non-destructive evaluation (NDE), stress analysis and damage tolerance simulations into the design process. Foundry process simulation is used to predict an array of porosity-related anomalies. The probability of detection of these anomalies is investigated with a radiographic inspection simulation tool (XRSIM). The likelihood that the predicted array of anomalies will lead to a failure is determined by a fatigue crack growth simulation based on the extended finite element method and therefore does not require meshing nor remeshing as the cracks grow. With this approach, the casting modeling provides initial anomaly information, the stress analysis provides a value for the critical size of an anomaly and the NDE assessment provides a detectability measure. The combination of these tools allows for accept/reject criteria to be determined at the early design stage and enables damage tolerant design philosophies. The methodology is applied to the design of a cast monolithic door used on the Boeing 757 aircraft.

Three Dimensional Modeling of Projection Radiography

The availability of a computer simulation for the X-ray projection image formation process, capable of modeling a rich variety of machine, configuration, and detector parameters, has a number of far reaching implications for quantitative nondestructive evaluation (NDE). The applications of such a tool occur both at the design stage and at the quality control inspection stages of the manufacturing process. Some of the notable uses include designing inspectability as a part of a computer aided design (CAD) package and developing an optimal inspection scheme for the component, while at the other end of the manufacturing process, a package of image processing routines, using the results of the forward model, can deconvolve a number of deterministic processes from the resulting radiograph. The promise of the potential applications of a quantitatively accurate forward model of the radiographic system has generated much interest in the basic physics of the process and the subsequent modeling of these processes.(1–5) For the model to be a flexible tool all of the various elements of an experimental equipment must be accurately described with enough variability to be useful over a large number of machines and experimental configurations.

Grain flow measurements with X-ray techniques

Abstract The use of low energy X-rays, up to 30 keV, densitometry is demonstrated for grain flow rate measurements through laboratory experiments. Mass flow rates for corn were related to measured X-ray intensity in gray scale units with a 0.99 correlation coefficient for flow rates ranging from 2 to 6 kg/s. Larger flow rate values can be measured by using higher energy or a higher tube current. Measurements were done in real time at a 30 Hz sampling rate. Flow rate measurements are relatively independent of grain moisture due to a negligible change in the X-ray attenuation coefficients at typical moisture content values from 15 to 25%. Grain flow profile changes did not affect measurement accuracy. X-rays easily capture variations in the corn thickness profile. Due to the low energy of the X-ray photons, biological shielding can be accomplished with 2-mm-thick lead foil or 5 mm of steel.

Using X-Rays for Multiphase Flow Visualization

Gas-liquid, gas-solid, liquid-solid, and gas-liquid-solid multiphase flows are difficult to visualize, characterize, and quantify because the systems are typically opaque. Invasive or noninvasive measurement methods are typically used for determining internal flow and transport characteristics of these complex flows. The difficulty with invasive methods is that they can alter the internal flow of a multiphase system causing interference with realistic process measurements. X-ray imaging provides one family of noninvasive measurement techniques used extensively for product testing and evaluation of static objects with complex structures. These techniques have been extended to visualize dynamic systems, such as those which characterize multiphase flows. This paper will describe a new X-ray flow visualization facility for large-scale multiphase flows. X-ray radiography and X-ray computed tomography of static and dynamic systems will be used to demonstrate system capabilities. Radiographic images will show bread dough rising, objects falling in a liquid, large bubbles rising in a 32 cm ID column of water, and operation of a 32 cm ID bubble column. X-ray computed tomography of a large static object will demonstrate visualization capabilities. X-ray computed tomography of a multiphase flow in a 32 cm bubble column will show local time-averaged gas holdup values for various operating conditions. Finally, challenges associated with X-ray stereographic imaging to capture time-resolved dynamic events will be outlined.Copyright

A CAD Interfaced Simulation Tool for X-Ray NDE Studies

Quantitative nondestructive evaluation, which aims at recovering information regarding certain parameters of the materials from the nondestructive evaluation (NDE) measurements, has attracted attention of the researchers in an increasing manner over the last decade. The work presented here represents the ongoing effort in quantitative nondestructive evaluation in the form of a computer simulation of the image formation process (1,2) and represents the x-ray component of broad effort to model all of the major inspection methods (3). To date one of the major limitation of this process modeling effort is the inability to handle complex part geometries. The developed code targets simulating x-ray inspection of parts designed through computer aided design (CAD) packages. For such a simulation tool to have practical applications, the physics of initial x-ray beam generation, x-ray and target interactions, x-ray and detector interactions should be modelled with sufficient accuracy and flexibility that the effects of the adjustable parameters found on the x-ray inspection systems can be simulated. While the physics in the undertaken work is modelled after well established principles, the information regarding the geometrical representation of the target object is provided by a CAD package through the developed interface.

Human body radiography simulations : development of a virtual radiography environment

A simulation program for x-ray methods is discussed. Computational algorithms for definition of x-ray sources, interactions of x-rays with complex objects and formation of images are developed from first principles. Subject geometries can be accessed from CAD definitions or from CT sets. The principles underlying the image formation process are introduced and images in industrial and medical x-ray applications are displayed.

Visualizing Fluid Flows With X-Rays

There are several methods available to visualize fluid flows when one has optical access. However, when optical access is limited to near the boundaries or not available at all, alternative visualization methods are required. This paper will describe flow visualization using an X-ray system that is capable of digital X-ray radiography, digital X-ray stereography, and digital X-ray computed tomography (CT). The unique X-ray flow visualization facility will be briefly described, and then flow visualization of various systems will be shown. Radiographs provide a two-dimensional density map of a three dimensional process or object. Radiographic images of various multiphase flows will be presented. When two X-ray sources and detectors simultaneously acquire images of the same process or object from different orientations, stereographic imaging can be completed; this type of imaging will be demonstrated by trickling water through packed columns and by absorbing water in a porous medium. Finally, local time-averaged phase distributions can be determined from X-ray computed tomography (CT) imaging, and this will be shown by comparing CT images from two different gas-liquid sparged columns.Copyright

RTSIM: A COMPUTER MODEL OF REAL-TIME RADIOGRAPHY

Real-time X-ray inspection is replacing film radiography in more and more applications. The rapid feedback provided by such systems greatly enhances throughput, especially in the case of complex objects requiring multiple views for complete inspection. When these systems are combined with powerful computing techniques, rapid image capture and enhancement and storage is possible. The productivity of these techniques would be increased with the ability to predict the sensitivity of a particular inspection without having to set up the equipment. Computer modeling of the inspection procedures can provide such information.

Resurrection of a reservoir sandstone from tomographic data using three-dimensional printing

Three-dimensional (3-D) printing provides an opportunity to build lab-testable models of reservoir rocks from tomographic data. This study combines tomography and 3-D printing to reproduce a sample of the Fontainebleau sandstone at different magnifications to test how this workflow can help characterization of transport properties at multiple scales. For this sandstone, literature analysis has given a porosity of 11%, permeability of 455 md, mean pore throat radius of 15 μm, and a mean grain size of 250 μm. Digital rock analysis of tomographic data from the same sample yielded a porosity of 13%, a permeability of 251 md, and a mean pore throat radius of 15.2 μm. The 3-D printer available for this study was not able to reproduce the sample’s pore system at its original scale. Instead, models were 3-D printed at 5-fold, 10-fold, and 15-fold magnifications. Mercury porosimetry performed on these 3-D models revealed differences in porosity (28%–37%) compared to the literature (11%) and to digital calculations (12.7%). Mercury may have intruded the smallest matrix pores of the printing powder and led to a greater than 50% increase in measured porosity. However, the 3-D printed models’ pore throat size distribution (15 μm) and permeability (350–443 md) match both literature data and digital rock analysis. The powder-based 3-D printing method was only able to replicate parts of the pore system (permeability and pore throats) but not the pore bodies. Other 3-D printing methods, such as resin-based stereolithography and photopolymerization, may have the potential to reproduce reservoir rock porosity more accurately.

Using Energy Dispersive X-Ray Measurements for Quantitative Determination of Material Loss Due to Corrosion

Corrosion is a general term for the oxidation process of metal. In the case of aircraft, corrosion on aluminum airframe skin can often be recognized by dulling or pitting of an area, and sometimes by the white powdery deposit of aluminum corrosion product. Corrosion in these areas means loss of aluminum material from the airframe skin. Thus corrosion can seriously affect the structural integrity of an aircraft unless proper inspection and maintenance is systematically performed. During heavy structural aircraft maintenance, corrosions are still defined mostly in a qualitative rather than a quantitative sense. The qualitative evaluations are biased and unpredictable because corrosions are extremely hard to detect and to predict in their early stages of formation.