Residency Abstracts

Hybrid additive manufacturing (AM) involves secondary processes or energy sources to alter specified locations within the build. Each hybrid step can refine the grain size, increase dislocation density, or modify residual stresses. Typically, the changes in mechanical properties are not confined within a single layer but have a compounding effect on preceding layers. Existing methods of measuring AM residual stress are limited in terms of their sensitivity, or they are destructive measurements. We propose using Resonant Ultrasound Spectroscopy (RUS) to noninvasively measure the residual stress in hybrid-AM components, based on changes to the resonant modes, compared to a stress-free component. In this paper, we use finite element models to simulate the residual stress in hybrid-AM components and to examine the sensitivity of RUS measurements in terms of frequency shifts and mode shapes with respect to specific layers of residual stresses.

Beam Plasma Interactions Experiment (Beam-PIE) is a NASA sounding rocket experiment that successfully ran in November 2023. Beam-PIE used space as a laboratory to explore wave generation from a modulated electron beam in the ionosphere. Its primary goal was to extend and build upon previous research from the BeamPIE study. The research involved exploring how particle accelerators in space generate waves and interact with particles, aiming to deepen our understanding of these phenomena in a space environment. This work is significant for advancing our knowledge of space plasma physics and the behavior of high-energy particles in such conditions.

Shock experiments were conducted on additively manufactured 316L stainless steel samples with 500-micron pores to investigate the collapse of the large pore and its effects on the shock wave propagation.

In this residency, I performed magneto-PL studies on our home-built microscope system. The system was built throughout the last two residencies and was finally ready for a series of dedicated measurements we intended to carry out. Unfortunately, the effect we hoped to see in avalanching nanoparticles did not manifest. A second project I performed in collaboration with Prashant Padmanabhan was the second harmonic generation study of BiTeI. Here, we used microscopy techniques developed at Columbia University to probe the surface domains in the BiTeI materials.

The project conducted at Los Alamos National Laboratory (LANL) will entail resonant ultrasound spectroscopy (RUS) experiments of additively manufactured (AM) 316 stainless steel (SS) hybrid-AM samples and conventional AM samples. Hybrid-AM manufacturing involves the use of secondary manufacturing processes and energy sources to alter specified layers within a build. These supplemental processes and energy sources act synergistically with the traditional as build parameters and alter microstructure, reduce the local average grain size, increase dislocation density, and impart or relieve residual stresses. Typically, the changes in mechanical properties are not confined within a single layer but rather have a compounding effect on the preceding layers. The ability to control material properties in localized regions of a build has significant part performance advantages, but the introduced changes present unique challenges in nondestructive evaluation (NDE). The project conducted at LANL is an attempt to resolve and understand the nondestructive inspection of these hybrid-AM components using RUS.

When materials are shocked and tear apart due to spall failure, the individual pieces from the original part have unique material characteristics due to the high stresses experienced during spall failure and may cause more or less damage then their unshocked counterparts. Therefore, developing an accurate model of the damage from an exploded material requires a deep understanding of the fragments' material characteristics as well as the material characteristics of the original part. I investigated the changes in material characteristics of martensitic steel that was shocked and experienced catastrophic failure to support the development of a more accurate computer model of martensitic steel's failure and range of effect.

The project involved examining the propagation of shock waves through various structures. Hopkinson bar testing was performed to achieve (relatively) mid-range strain rates in lattices, some bistable and some with varied geometry. High speed video with digital image correlation data was taken of these tests, allowing the examination of the propagation of the shock through the lattices. At the same time, modeling and simulation was performed of previously run high strain rate shock propagation in 3D printed structures.

For residency II, I was able to construct an operational magneto-PL setup and subsequently rebuilt the magneto-THz setup in the lab. Currently, very few groups in the world have simultaneous magneto-PL and magneto-THz setups in the same lab. Upon the successful construction of the two setups, I hope to utilize residency III to continue spectroscopic studies on nanomaterials.

My first residency was through Los Alamos National Laboratories. During this residency, I learned to apply the LANL ASC Multiphysics FLAG code, an arbitrary Lagrangian-Eulerian (ALE) code with MHD and advanced material models, to my research on electrothermal instability physics. This multi-dimensional, multi-material, multi-temperature code has been used to study fundamental ETI physics, and continues to evolve to address more topics in the HED regime. Direct comparisons of FLAG calculations to A/lambda and ED target designs are well-suited to address the role of dominant, localized Joule heating and ETI in plasma formation in high-current conductors. I studied magneto Rayleigh-Taylor (MRT) evolution and relevant physics using the FLAG code, and was able to both qualitatively and quantitatively compare these simulations to experimental and theoretical data. These comparisons showed excellent agreement.

For residency II, I was able to construct an operational magneto-PL setup and subsequently rebuilt the magneto-THz setup in the lab. Currently, very few groups in the world have simultaneous magneto-PL and magneto-THz setups in the same lab. Upon the successful construction of the two setups, I hope to utilize residency III to continue spectroscopic studies on nanomaterials.

A systematic study was undertaken employing phase field dislocation dynamics (PFDD), a powerful physics-informed meso-scale model, to investigate the influences of material properties and void obstacle geometries on nanovoid strengthening in fcc metals. Of particular interest was the impact of dislocation dissociation, a common occurrence in fcc metals, on the strengthening trends as well as the mechanisms active for dislocations to overcome nanovoid obstacles.

ANPs have emerged as potentially hyperresponsive nanomaterials for environmental sensing. Due to the extreme optical nonlinearities and reliance on sensitive cross-relaxation pathways within the nanoparticle, small perturbations in the nanoparticle’s environment manifest into large changes in luminescence intensities of the ANP’s optical emission. In the realm of nanoscale sensing, ANPs have previously demonstrated notable changes in luminescence intensities when changes in pressure, temperature, and material substrates were applied to the nanoparticles. In this residency, we further explored ANP sensing in areas of high fields, such as high electric and magnetic fields.

There were two primary goals to this residency project. The first goal was for me to learn the theory of molecular dynamics and application through LAMMPS. This was accomplished by me reading literature in parallel with scripting progressively more advanced simulations. The second goal was for me to test LAVA with the perspective of a newcomer to LAMMPS before its release. LAVA is a Python code named with the “La” in LAMMPS and the “VA” in VASP and can perform molecular dynamics and atomistic in a semi-automated fashion with each of these software, respectively. The intent is to provide a method for those inexperienced with such simulations to still produce results, and to streamline the production pipeline for more experienced users with automation tools.

ANPs have emerged as potentially hyperresponsive nanomaterials for environmental sensing. Due to the extreme optical nonlinearities and reliance on sensitive cross-relaxation pathways within the nanoparticle, small perturbations in the nanoparticle’s environment manifest into large changes in luminescence intensities of the ANP’s optical emission. In the realm of nanoscale sensing, ANPs have previously demonstrated notable changes in luminescence intensities when changes in pressure, temperature, and material substrates were applied to the nanoparticles. In this residency, we further explored ANP sensing in areas of high fields, such as high electric and magnetic fields.

Current literature for impact of Stacking Fault Energy (SFE) on critical stress for a dislocation to shear a void is limited to atomistic models, which have well known spatial and temporal limitations. Further, the limited availability of robust interatomic potentials for various fcc transition metals means that complete, systematic studies focusing on the importance of SFE for void shearing are lacking. Adding SFE to dissociated dislocations in a meso-scale model such as Phase Field Dislocation Dynamics (PFDD) will allow for more accurate predictions of void hardening effects in fcc metals, as well as further the PFDD model. This added physics is a crucial step towards the goal of accurately predicting dislocation mediated pore growth in a meso-scale PFDD model. For this residency, the PFDD model developed by the Beyerlein group at UCSB was used as the meso-scale model within which SFE physics was included. Five fcc transition metals, Copper, Silver, Nickel, Platinum, and Rhodium, were used and edge dislocations were allowed to dissociate into Shockley partials. Working together with my LANL advisor, a project framework was devised to systematically investigate the effect of SFE on the obstacle strength of nanovoids. The edge dislocations were allowed to shear an array of voids under stress, with the void sizes and spacings varied for each metal. Critical stress values were calculated for each void size and spacing, and results were compared and contrasted with current literature.

In this project, we determined the principle of photon energy down conversion, where high-energy X-ray photon energies get attenuated down to