Juan P Escobedo-diaz

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.

Zirconium: Probing the Role of Texture using Dynamic-Tensile-Extrusion

The effect of high strain-rate and high strains on mechanical behavior has been observed primarily in isotropic, cubic materials. The behavior of low-symmetry, textured, materials is not as well understood. To examine the high strain and high strain-rate response of structural metals, a Dynamic Tensile Extrusion technique has been developed at Los Alamos National Laboratory. In this study, high-purity zirconium bullets were accelerated up to velocities of 615m/s and extruded through a high-strength steel die. The Zr bullets were fired at 23°C and 250°C. Specimens were sectioned in two orthogonal directions from the as received plate: (1) loading direction aligned in plane (IP) to the rolling direction and (2) loading direction through thickness (TT) of the plate. A combination of in-situ and ex-situ characterization techniques has been used to study the response of Zr under this dynamic loading condition. Not only are these the first experiments of their kind performed at temperatures higher than room temperature, but high-speed imaging and for the first time, PDV (Photonic Doppler Velocimetry) has been employed to capture the time and velocity of the evolved deformation through the die.

Influence of Texture and Temperature on the Dynamictensile-Extrusion Response of High-Purity Zirconium

To create comprehensive models of mechanical deformation in Zirconium (Zr) it is important to observe the effect of high strain on the material. The mechanical behavior and damage evolution in textured, high-purity zirconium (Zr) is influenced by strain rate, temperature, stress state, grain size, and texture. In particular, texture is known to influence the slip-twinning response of Zr, which directly affects the work hardening behavior at both quasi-static and dynamic strain rates. However, while microstructural and textural evolution of Zr in compression and to relatively low strains in tension has been studied, little is understood about the dynamic, high strain, tensile response of Zr. Here, the influence of texture on the dynamic, tensile, mechanical response of high-purity Zr is correlated with the evolution of the substructure. Experiments will be conducted using dynamic-tensile-extrusion process. A bullet-shaped sample has been impacted into a high-strength steel extrusion die and soft recovered in the Taylor Anvil Facility at Los Alamos National Laboratory. Finite element modeling that employs a continuum level constitutive description of Zr will be performed to provide insight into the dynamic extrusion process. Current experimental findings will be presented.