Brian M. Patterson

Dimensional quantification of embedded voids or objects in three dimensions using X-ray tomography.

Scientific digital imaging in three dimensions such as when using X-ray computed tomography offers a variety of ways to obtain, filter, and quantify data that can produce vastly different results. These opportunities, performed during image acquisition or during the data processing, can include filtering, cropping, and setting thresholds. Quantifying features in these images can be greatly affected by how the above operations are performed. For example, during binarization, setting the threshold too low or too high can change the number of objects as well as their measured diameter. Here, two facets of three-dimensional quantification are explored. The first will focus on investigating the question of how many voxels are needed within an object to have accurate geometric statistics that are due to the properties of the object and not an artifact of too few voxels. These statistics include but are not limited to percent of total volume, volume of the individual object, Feret shape, and surface area. Using simple cylinders as a starting point, various techniques for smoothing, filtering, and other processing steps can be investigated to aid in determining if they are appropriate for a specific desired statistic for a real dataset. The second area of investigation is the influence of post-processing, particularly segmentation, on measuring the damage statistics in high purity Cu. The most important parts of the pathways of processing are highlighted.

Measure of morphological and performance properties in polymeric silicone foams by X-ray tomography

In the absence of nuclear weapons testing, assuring comparable material performance for replacement of no-longer-available material with modern formulations is difficult. The replacement material must completely replicate the performance of the original. Quantification of morphological characteristics in three dimensions by micro X-ray computed tomography (μCT) lends statistics and property values not otherwise achieved. This allows for the measurement of lot-to-lot, synthesis formula variations, as well as pre- and post-experimental structural changes that would be invisible to qualitative image comparison techniques. Owing to the unavailability of the original material, several novel formulations of poly(dimethylsiloxane) (PDMS) foams were imaged and quantitatively compared to aid in choosing a replacement material. In this study, bulk properties were measured with μCT including, percent void volume, average void equivalent diameter and others, and were collected for four different formulations of PDMS foams from pristine, return for service, as well as samples that were aged by gamma ray exposure. Performance characteristics (e.g., Poisson ratio) were measured and compared. From this study, we will be able to provide more information for the selection of the material that most closely matches the performance of the original material.

Attenuated Total Internal Reflection Infrared Microspectroscopic Imaging Using a Large-Radius Germanium Internal Reflection Element and a Linear Array Detector

The number of techniques and instruments available for Fourier transform infrared (FT-IR) microspectroscopic imaging has grown significantly over the past few years. Attenuated total internal reflectance (ATR) FT-IR microspectroscopy reduces sample preparation time and has simplified the analysis of many difficult samples. FT-IR imaging has become a powerful analytical tool using either a focal plane array or a linear array detector, especially when coupled with a chemometric analysis package. The field of view of the ATR-IR microspectroscopic imaging area can be greatly increased from 300 × 300 μm to 2500 × 2500 μm using a larger internal reflection element of 12.5 mm radius instead of the typical 1.5 mm radius. This gives an area increase of 70× before aberrant effects become too great. Parameters evaluated include the change in penetration depth as a function of beam displacement, measurements of the active area, magnification factor, and change in spatial resolution over the imaging area. Drawbacks such as large file size will also be discussed. This technique has been successfully applied to the FT-IR imaging of polydimethylsiloxane foam cross-sections, latent human fingerprints, and a model inorganic mixture, which demonstrates the usefulness of the method for pharmaceuticals.

Dimensional standard for micro X-ray computed tomography.

The decrease in the cost of high end computing and the availability of high quality X-ray sources in the laboratory environment has led to an increased use of three-dimensional (3D) X-ray micro computed tomography (μCT). In the medical community, the primary concern for CT is calibrating for X-ray absorption and ascertaining the difference between healthy tissue and cancerous tissue or examining fractures. Absorption calibration is also important in the materials community, however confirming dimensional accuracy of voids, defects, machined parts, cracks, or the distribution of dispersed particles is typically more important. One key aspect of μCT that is often overlooked in the literature is the number of radiographs required for dimensional accuracy of the 3D reconstruction and minimization of image noise. In μCT, a number of radiographs are collected in theta increments as the sample is rotated at least 180°. They are typically collected in 1° increments (or 181 radiographs), 0.25° increments (721 radiographs), or some other multiple. The question that arises, especially in a laboratory based instrument, where the required exposure times are longer to get high-quality signal-to-noise compared to synchrotron sources, is what is the optimal number of images required to reach the volumetric statistics of the sample, and minimize the noise while not overly scanning the sample at a cost in time? A dimensional standard based upon NIST certified glass microspheres dispersed in a low density poly(styrene) matrix to answer this question is proposed. Experiments are shown that describe the microsphere size statistics as a function of number of radiographs calculated using a commercial software package, AvizoFire. These results are important in understanding the distribution of voids in a foam and confirming the accuracy of the 3D measurements obtained.

Proton Radiography Peers into Metal Solidification

Historically, metals are cut up and polished to see the structure and to infer how processing influences the evolution. We can now peer into a metal during processing without destroying it using proton radiography. Understanding the link between processing and structure is important because structure profoundly affects the properties of engineering materials. Synchrotron x-ray radiography has enabled real-time glimpses into metal solidification. However, x-ray energies favor the examination of small volumes and low density metals. Here we use high energy proton radiography for the first time to image a large metal volume (>10,000 mm3) during melting and solidification. We also show complementary x-ray results from a small volume (<1 mm3), bridging four orders of magnitude. Real-time imaging will enable efficient process development and the control of structure evolution to make materials with intended properties; it will also permit the development of experimentally informed, predictive structure and process models.

Infrared Microspectroscopic Imaging Using a Large Radius Germanium Internal Reflection Element and a Focal Plane Array Detector

Previously, we established the ability to collect infrared microspectroscopic images of large areas using a large radius hemisphere internal reflection element (IRE) with both a single point and a linear array detector. In this paper, preliminary work in applying this same method to a focal plane array (FPA) infrared imaging system is demonstrated. Mosaic tile imaging using a large radius germanium hemispherical IRE on a FPA Fourier transform infrared microscope imaging system can be used to image samples nearly 1.5 mm × 2 mm in size. A polymer film with a metal mask is imaged using this method for comparison to previous work. Images of hair and skin samples are presented, highlighting the complexity of this method. Comparisons are made between the linear array and FPA methods.

Reactive, anomalous compression in shocked polyurethane foams

We present the results of plate impact experiments performed on 30%–75% porous, polymeric methylene diphenyl diisocyanate polyurethane foams. The combination of new data with those previously obtained on full-density material was used to calibrate complete equations-of-state under both inert and chemically reactive frameworks. Description of unreacted polyurethane was based on a combination of Hayes and P-α models, whereas its decomposition products were predicted via free energy minimization under the assumption of chemical and thermodynamic equilibrium. Correspondence of experiment and theory suggests that polyurethane at all densities decomposes when shocked above some threshold pressure, and that this threshold falls dramatically as a function of initial porosity. The shock locus of foams at 50% or less of theoretical maximum density was found “anomalous” in the sense that final volumes increased with pressure. We attribute this anomaly to chemical decomposition of the initial matrix to a mixture of s...

Manufacturing complex silica aerogel target components

Abstract Aerogel is a material used in numerous components for inertial confinement fusion and high-energy density physics targets. In the past, these components were molded into the proper shapes. Artifacts left in the parts from the molding process, contour irregularities from shrinkage, and density gradients caused by the skin have caused Los Alamos National Laboratory to pursue machining as a way to make the components. The machining of aerogel is an involved process, and many manufacturing aspects need to be considered including holding the material for machining, achieving the desired surface roughness and the desired dimensional accuracy, conceivably producing a part with enhanced dimensional tolerance and minimal density variations. Therefore, an effort has been established to develop a method to more accurately determine density errors, perform machining experiments, acquire physical property data, and model the machining process.

Dynamic damage nucleation and evolution in multiphase materials

For ductile metals, dynamic fracture occurs through void nucleation, growth, and coalescence. Previous experimental works in high purity metals have shown that microstructural features such as grain boundaries, inclusions, vacancies, and heterogeneities can act as initial void nucleation sites. However, for materials of engineering significance, those with, second phase particles it is less clear what the role of a soft second phase will be on damage nucleation and evolution. To approach this problem in a systematic manner, two materials have been investigated: high purity copper and copper with 1% lead. These materials have been shock loaded at ∼1.5 GPa and soft recovered. In-situ free surface velocity information and post mortem metallography reveals the presence of a high number of small voids in CuPb in comparison to a lower number of large voids in Cu. This suggests that damage evolution is nucleation dominated in the CuPb and growth dominated in the pure Cu.

Integrating X-ray fluorescence and infrared imaging microspectroscopies for comprehensive characterization of an acetaminophen model pharmaceutical.

The integration of full spectral images using the complementary microspectroscopic imaging techniques X-ray fluorescence and Fourier transform infrared is demonstrated. This effort surpasses previous work in that a single chemometric software package is used to elicit chemical information from the integrated spectroscopic images. Integrating these two complementary spectroscopic methods provides both elemental and molecular spatial distribution within a specimen. The critical aspect in this work is using full spectral maps from each pixel within the image and subsequent processing with chemometric tools to provide integrated chemical information. This integration enables a powerful approach to more comprehensive materials characterization. Issues addressed include sample registration and beam penetration depth and how each affects post-processing. An inorganic salt and an acetaminophen pharmaceutical model mixture demonstrate the power of integrating these techniques with chemometric software.