Tyler Stannard

Synchrotron-based X-ray computed tomography during compression loading of cellular materials

Three-dimensional X-ray computed tomography (CT) of in situ dynamic processes provides internal snapshot images as a function of time. Tomograms are mathematically reconstructed from a series of radiographs taken in rapid succession as the specimen is rotated in small angular increments. In addition to spatial resolution, temporal resolution is important. Thus temporal resolution indicates how close together in time two distinct tomograms can be acquired. Tomograms taken in rapid succession allow detailed analyses of internal processes that cannot be obtained by other means. This article describes the state-of-the-art for such measurements acquired using synchrotron radiation as the X-ray source.

Applying Pattern Recognition to the Analysis of X-ray Computed Tomography Data of Polymer Foams

X-ray computed tomography (CT) of materials provides large, three dimensional (3D) image data sets (i.e., tomograms), resolving both surface and subsurface features. Tomograms of open-cell polymer foams typically reveal a two-phase material consisting of the supporting polymer ligament material and the void structure (Fig. 1, left). Segmenting the tomograms for the void structure, rather than the polymer ligaments, allows for measuring the void structures in 3D (Fig. 1, right). The equivalent diameter of a void, which is the measure of the void diameter assuming the void is a perfect sphere, is a common singular metric used to describe and differentiate polymer foams. However, for stochastic and irregular void structures, this singular metric can be insufficient when comparing two or more polymer foam samples (Fig. 2). Therefore, multiple 3D void descriptors are typically required, though more than three measurements can lead to difficulty in interpretation. Thus, a statistically-based pattern recognition technique, Principal Components Analysis (PCA), has been implemented to aid in the interpretation of multivariate tomogram data sets of polymer foam systems. PCA transforms N-dimensional data into a reduced number of dimensions which capture most of the data’s variance and is commonly used for pattern recognition in experimental sciences, thus enabling easy visualization of sample groupings based on several descriptors.

Feasibility of using LiMnO 2 batteries for nuclear forensics

Lithium-ion batteries, which are widely used in consumer electronics, have the potential to serve as neutron detectors after a nuclear detonation. Their small size permits collection of many samples for subsequent investigations. Besides a large cross section in the 6Li(n,α)3H reaction, there are multiple possible neutron threshold detector materials in the battery. Inductively coupled plasma mass spectrometry provided detailed material information on a coin-cell LiMnO2 battery. With this trace element analysis measuring Fe, Mn, Cr, Ni, Al, Na, Cu and Co, the possible reactions, their threshold energies and products were tabulated. This study performed MCNP modeling of battery exposure to neutrons from a detonation and comparison to experimental results from reactor irradiated batteries. As nearly all of the resulting radionuclides are photon emitters, the gamma spectrum can be obtained without disassembling the batteries. Two sets of gamma spectra were measured 1 to 3 days after the exposure to mimic the latency anticipated between device detonation and the collection and measurement of samples in the event of an actual incident.

Li-Ion Batteries Used as Ubiquitous Neutron Sensors for Nuclear Forensics

With an increasingly complex worldwide nuclear environment, nuclear forensics provides a deterrent through proper attribution. Identifying the type of event is important in the attribution process, and the lithium battery has the potential to provide significant information for this purpose. The incident neutron spectral fluence is related to the type of nuclear event. The lithium battery is built using materials that can be used to assess the number of incident neutrons, as well as provide threshold detection dependant on the neutron energy. This study looks at correlating the production of various long-lived radioactive isotopes to the incident neutron spectrum. The analysis uses known nuclear cross sections and battery properties to calculate the number of long-lived radioactive elements that can be produced in the solid winding of the active battery elements, which include the cathode, separator, and anode. Some isotopes are only produced above a threshold energy, such as 58Co , which requires 10.6 MeV neutrons. Other isotopes such as 3H are produced through various reaction channels, mostly 6Li(n,α)3H, which is an exothermic reaction, and is not associated with a threshold energy.

Multimodal 3D Time-Lapse Studies of Corrosion Pitting and Corrosion-Fatigue Behavior in 7475 Aluminum Alloys

Tyler Stannard, Hrishikesh Bale, Thomas Chengattu, Sridhar Niverty, Jason Williams, Xianghui Xiao, Arno Merkle, Erik Lauridsen, Nikhilesh Chawla 1. Center for 4D Materials Science, Arizona State University, Tempe United States. 2. Carl Zeiss X-Ray Microscopy, Pleasanton United States. 3. Advanced Photon Source, Argonne National Laboratory, Lemont United States. 4. Xnovo Technology ApS, Koege Denmark.

Micro-scale X-ray Computed Tomography of Additively Manufactured Cellular Materials under Uniaxial Compression

Additively manufactured (AM) materials are a current “hot topic” in materials science.[1] Current investigations of AM cellular materials, such as polymer foams, include the mechanical performance under compressive strain using 3D X-ray computed tomography (CT) at the microscale. This allows for an enhanced visualization of processes such as void collapse, brittle fracture, and increased surface area of AM materials while undergoing compressive strain. The results from this study will include interrupted in situ compression of AM polymer foams using laboratory-based CT as well as dynamic compression of AM polymer foams using synchrotronbased CT.