Presenters

Dendritic deformation modes in additive manufacturing revealed by operando x-ray diffraction

 Adrita Dass

Manufacturing, Design, and Materials

Dynamic solidification behavior during metal additive manufacturing directly influences the as-built microstructure, defects, and mechanical properties of printed parts. How the formation of these features is driven by temperature variation (e.g., thermal gradient magnitude and solidification front velocity) has been studied extensively in metal additive manufacturing, with synchrotron x-ray imaging becoming a critical tool to monitor these processes. Here, we extend these efforts to monitoring full thermomechanical deformation during solidification through the use of operando x-ray diffraction during laser melting. With operando diffraction, we analyze thermomechanical deformation modes such as torsion, bending, fragmentation, assimilation, oscillation, and interdendritic growth. Understanding such phenomena can aid the optimization of printing strategies to obtain specific microstructural features, including localized misorientations, dislocation substructure, and grain boundary character. The interpretation of operando diffraction results is supported by post-mortem electron backscatter diffraction analyses.

Grand alloying: Enabling Multi-Phase Co-existence in Additive Manufactured Titanium Alloys

Jenniffer Bustillos

Additive Manufacturing

Beam-based additive manufacturing (AM) has shown promise in enhancing the strength of Titanium alloys through the formation of fine microstructures. However, this improvement comes at the expense of reduced work hardening and ductility. To overcome these limitations, we introduce the concept of “grand alloying,” involving the combination of multiple commercial alloys during the AM process. This approach aims to circumvent incompatibility in multi-alloy structures by achieving a random or site-specific distribution of multiple phases. Through the integration of operando high energy x-ray diffraction during laser-based Direct Energy Deposition (L-DED) of a binary grand alloy, and comprehensive microstructural investigations at multiple length-scales, we identify key factors such as: high cooling rates, localized diffusion, and laser-induced convective forces, that play a crucial role in achieving phase co-existence. This work sheds light on the role of dynamic phase evolution and microstructure to advance the design of alloys for AM through innovative techniques.

Interfacial Strength in Single Particle Impact-Induced Bonding

Qi Tang

Solid Mechanics

Metallurgical bonding and material buildup during cold spray occur by high-velocity impact of micrometer-sized metallic particles onto metallic substrates. The nanosecond time scale and the micrometer length scale involved in the impact-induced bonding of individual particles make the systematic studies of the process-microstructure-property relationships challenging. In this study, we use laser-induced microparticle impact tests to image and produce bonded single particles with precisely measured particle sizes and velocities. Next, we use micromechanical testing inside a scanning electron microscope to measure the interfacial strength and observe interfacial fracture in real time. Finally, by integrating the insights from the two in-situ approaches, we discuss the relationships between impact velocity, particle size and interfacial strength in impact bonding.

Leveraging High Energy X-ray Diffraction for Characterization of Micromechanical Behavior in Polycrystalline Engineering Materials

Solid Mechanics

Synchrotron light sources are invaluable scientific tools for performing in-situ x-ray experiments for better understanding materials used in engineering design. Producing extremely high energy and high flux x-rays, these facilities allow scientists and engineers alike to probe engineering materials on the microscopic scale and tackle real-world material problems that plague design. High Energy X-ray Diffraction Microscopy (HEDM) is an x-ray diffraction technique used for characterizing microstructures within polycrystalline materials through two modalities: far-field HEDM and near-field HEDM. In-situ far-field HEDM mechanical loading experiments provide grain average measurements such as orientation, position, and the elastic strain state of the polycrystalline microstructures. Near-field HEDM provides spatial resolution of the sample and can be used to generate 3-D microstructure mappings, often for sake of creating comparable computational models. The unfortunate reality is that conducting an efficient HEDM experiment is quite challenging – experimental setup and the material itself can introduce unique and unforeseen complexities. Heroic efforts to create tools for planning and optimizing these x-ray diffraction experiments both a prioi and during are being done to ensure that synchrotron users get the utmost value out of their beamtimes. One tool in particular, the Virtual Diffractometer, intends to allow for virtual simulation of an HEDM experiment a prori providing invaluable insight to users if the material of interest is suitable for HEDM and if the experimental signatures they seek can be seen via this method. Optimization of these x-ray diffraction experiments will help to ensure the conduction of efficient scientific work and further progress in the associated academic fields of research.

Ellen van Wijngaarden

People are turning to biologically produced materials as an alternative to traditional materials such as metals and plastics. Biomanufactured materials offer an alternative to petrochemically derived materials as well as additional benefits including low resource investment and relatively low temperatures needed for production. However, many biologically produced materials are not mechanically comparable to synthetically produced materials and require complex and lengthy purification processes before use. Biomanufactured bacterial polysaccharides come with many advantages relative to other biofilm components, such as being biodegradable and mechanically robust. This study 1) identifies the material properties of a novel polysaccharide, called promonan, isolated from the extracellular polymeric substances from Sphingomonas sp. LM7 2) demonstrates that these properties can be manipulated to suit specific applications and 3) successfully shortens the required purification process while maintaining material stiffness.

Wave Energy Optimization

Rebecca McCabe

Sustainability and Systems Optimization

Wave energy converters (WECs) can advance the global energy transition by producing clean power for utility grids and offshore technologies. This presentation describes (1) a systems optimization framework to determine the ideal WEC design considering techno-economic viability and environmental impacts at the industry level; and (2) an implementation of the techno-economic portion of this optimization for one WEC concept.

The proposed framework combines aspects of multidisciplinary design optimization, control co-design, life cycle analysis, techno-economic analysis, and systems engineering to suggest a suite of value metrics, a process for metric weighting, and an integrated WEC design methodology. The process articulated here can generalize to other emerging energy technologies, ultimately advancing the energy sector decarbonization.

The implementation section presents results for the multiobjective optimization of a two-body point absorber WEC design benchmark. The geometry and controller parameters are optimized using sequential quadratic programming to minimize the levelized cost of energy (LCOE) and the coefficient of variation of power. Parameter sensitivities and a Pareto tradeoff curve are shown. Two different hydrodynamic methods are compared: an accurate analytical solution to the 3D boundary value problem using Bessel functions, and a simplified analytical solution that approximates wave diffraction. Structures, energy storage, and controller force saturation are taken into account, and the implications for WEC design are discussed.

Climate Engineering: The World’s Biggest Feedback Controls Problem

Ezra Brody

Climate Engineering

The planet is warming at an alarming rate, and greenhouse gas emission reductions may not happen fast enough to avoid catastrophic outcomes. One potential way to address this that has been gaining attention lately is solar radiation modification (SRM), which involves reflecting a small portion of sunlight back into space, thus cooling the earth’s surface. The two methods that have received the most research attention are stratospheric aerosol injection (SAI) and Marine Cloud Brightening (MCB). This talk will discuss the history of research on feedback controls in SAI, as well as current and future pioneering research on feedback controls in MCB.

A Dynamic Deployment: Starts, Stops, and Target Shifts of Stratospheric Aerosol Injection

Jared Farley

Climate Engineering

Stratospheric Aerosol Injection (SAI) would involve the addition of sulfate aerosols in the stratosphere to reflect part of the incoming solar radiation, thereby cooling the climate. Studies trying to explore the impacts of SAI have often focused on idealized scenarios, with consistent deployment and strategy. By introducing inconsistencies in SAI, we can examine a broader spectrum of potential scenario-related risks. We simulate a few representative inconsistencies in a pre-existing SAI scenario: an abrupt termination, a decade-long gradual phase-out, and 1-year and 2-year temporary interruptions of deployment. After examining their climate impacts, we use these simulations to train an emulator, and use this to project temperature response for a broader set of inconsistencies.

The criticality of transition to inertial shear thickening close to jamming

Nishanth Murugan

Fluid Mechanics

Dense non-Brownian suspensions exhibit a transition in which their shear viscosity from a constant value at low shear rates to a linearly increasing function when inertia becomes important. Experiments on the shear rheology of frictionless non-Brownian suspensions have revealed the critical shear rate for this transition to sensitively depend on the volume fraction (phi) of the suspension. However, experimental studies of frictional suspensions have been observed a transition that is independent of phi. This necessitates a better understanding and method of characterizing the suspension microstructure associated with the transition. In this work, we use Discrete Element Method (DEM) simulations to examine the critical shear rate of this transition in a dense frictionless suspension. To model frictionless interactions between particles, we design a repulsive force that activates when the surface separation between particles is smaller than a given threshold. Our simulations show that the critical shear rate is indeed sensitive to the volume fraction (phi) of the suspension, and that it goes to zero as we approach the jamming volume fraction phi-m of the suspension. We rationalize the drop in the critical shear rate to be associated with the growing length scale of the microstructure as approaches phi-m. We justify this statement by employing a crossover scaling framework which yields a universal collapse of the rheological data in dense suspensions with a broad range of volume fractions and shear rates.

Golden eagles exploit turbulence intermittency

Dipendra Gupta

Fluid Dynamics

We examine the statistics of the accelerations of six golden eagles in natural flight and find that extreme vertical accelerations are consistent with the selective amplification of small-scale turbulent updrafts. The finding appears to be the first observation of wildlife exploiting turbulent fluctuations, and extends what we know about how wildlife uses relatively stationary flows to stay aloft, such as thermal updrafts and wind shear, by showing how fully unsteady flows, or gusts, can also be beneficial. The evidence in favor of our interpretation includes a probability distribution of vertical acceleration differences that exhibits long tails consistent with turbulence intermittency and inconsistent with gust suppression, or with the mitigation of extreme events. Furthermore, the breadth of the tails, measured by the acceleration difference flatness, increases toward short timescales, thereby breaking self-similarity in the same way as does turbulence intermittency. Finally, the acceleration difference flatness blows up toward large values on timescales shorter than a few seconds in a way predicted by a simple nonlinear model of the eagles’ response to turbulence. The model breaks up-down symmetry in favor of upward gusts, and is consistent with the eagles’ interest in staying aloft while minimizing energy expenditure.

Electrospray propulsion Surface Interaction Diagnostics

Giuliana Hofheins

Aerospace/Electric Propulsion

Electrospray thrusters are a subset of electric propulsion systems that use conductive ionic liquids as propellants, where high potentials electrostatically accelerate ions from a sharp emitter tip to form a plume. Both experiments and simulation indicate that particles from the plume impact thruster and spacecraft surfaces like the extractor electrode, resulting in propellant accumulation and eventual device failure. Secondary ion mass spectrometry is a well-established surface composition diagnostic technique where collisions of high energy, generally atomic, ion beams with surface of interest give rise to sputtered cloud neutrals and charged particles that can be analyzed via time of flight mass spectrometry. By utilizing an electrospray plume as the high energy primary ion beam, the charged products that result from impacts with surfaces of interest will be examined. The design of electrospray TOF-SIMS as a diagnostic system will include a tungsten-needle ion source operating with ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), a modular sample and extractor assembly, and a time of flight mass spectrometer. Preliminary results include secondary species yields as a function of primary ion beam energy and surface matrix.

Multi-Disciplinary Design Optimization of a Cislunar Spacecraft Supply Logistics

Arthur Chadwick

Aerospace Engineering

StarLift is intended to provide guidance on what a cislunar space systems spacecraft design and mission architecture may look like for intercepting, servicing, and provisioning other spacecraft. Orbiting satellites typically adhere to a non-refuelable and non-serviceable mission architecture translating to decreased mission lifetime, lowered return on investment, and prevention of potentially viable architectures. In this work, we analyze the orbit raising aspects of a Low Earth Orbit (LEO) space system architecture using a multidisciplinary design optimization (MDO) framework in MATLAB. Design variables include specific impulse, structural mass, and initial orbit radius of the spacecraft. Model assumptions (constraints) are initial and final circular orbits, as well as an orbit raise of twice its initial orbit. An initial exploration of the design space and objectives was conducted using a Design of Experiments (DoE). The single objective optimization (SOO) minimizes the total thrust, while the multi-objective optimization (MOO) minimizes the total thrust and total time. Both optimizations employ the heuristic method Simulated Annealing (SA) algorithm. The SOO reveals a more optimal design not found in the DoE, emphasizing the importance of high specific impulse. The MOO shows the tradeoff between total thrust and total time in the Pareto Front, as well as the design closest to the utopia point. The preliminary MOO optimal design (initial orbit radius of 6575 km, structural mass of 1290 kg, and specific impulse of 4990 sec) achieves a total thrust of 6.8 N in 0.78 years. Future work shall 1) add modules like cost, power, and orbital mechanics to adapt to cislunar space, 2) increase the analysis fidelity of the relationship between specific impulse and structural mass, 3) employ constraints for each type of propulsion system, and 4) ensure analysis includes high Technical Readiness Level (TRL) spacecraft.