Collaborative research: Unraveling the mechanisms behind acoustoplasticity using a multiscale computational and in-situ, time resolved experimental approach
Acoustoplasticity is a phenomenon where softening of metallic structures is induced by quasi-static and dynamic elastic waves. They have been proven to be useful in several manufacturing applications including ultrasonic additive manufacturing, extrusion, welding, flip-chip bond, and several others. Despite several novel applications, the methodology is predominantly based on empirical knowledge. This award supports fundamental research to decipher the complex mechanisms behind acoustoplasticity using a combined computational and experimental analysis. This knowledge will help us in improving the aforementioned applications and widen their applicability. In addition to the direct scientific benefits, improved understanding of ultrasonic additive manufacturing will have major economic benefits as we transition to in-space manufacturing. This award will support cross-cutting research between material science, multiscale mechanics, and material characterization methods. Student recruitment will focus on underrepresented minorities and the students will collaboratively work on computation and experimental methods. To facilitate broader dissemination, hands-on experimental workshops targeting K-8 school children and school teachers will be organized.
Despite the large body of work on the use of acoustoplasticity for several novel applications, there is a lack of fundamental understanding of the mechanics behind acoustoplasticity. This can be attributed to three main reasons: (1) acoustic excitation occurs in the macroscale, but its effects can be spread over orders of magnitude in the spatio-temporal scale; (2) single-scale models smear out the mechanisms spread over multiple scales and cannot address the full complexity of it; (3) probing the acoustic-affected dislocation plasticity is not trivial due to the fast time scale of the events. This research will fill these knowledge gaps by combining three techniques: multiscale simulations, time resolved nonlinear waves, and microscopy. The complex dynamics of dislocations in plastic deformation of materials under imposed acoustic waves will be characterized using Concurrent Atomistic-Continuum simulations. The in-situ, time-resolved experimental characterization methods will help in capturing the fast mechanisms. Finally, a multiscale parameter will be used to bridge the multiple spatio-temporal scales between the simulations and experiments.
Overview: Acoustoplasticity is a class of phenomenon where softening of metallic structures is induced by quasi-static and dynamic elastic waves. They have been proven to be useful in several manufacturing applications including ultrasonic additive manufacturing, extrusion, welding, flip-chip bond, and several others. Despite the large body of work on the use of this phenomenon for several novel applications, there is a lack of fundamental understanding of the mechanics behind acoustoplasticity. This can be attributed to three main reasons: (1) acoustic excitation occurs in the macroscale, but its effects can be spread over 6 orders of magnitude in the spatio-temporal scale; (2) single-scale models smear out the mechanisms spread over multiple scales and cannot address the full complexity of it; (3) probing the acoustic-affected dislocation plasticity is not trivial due to the fast time scale of the events. Without a quantitative understanding of acoustoplasticity, there will be no adequate scientific basis for wider applications of this phenomenon. The goal of this proposal is to develop a bottom-up understanding of acoustoplasticity through an integrated multiscale computational and experimental analysis. To accomplish this goal, several specific objectives will be fulfilled:
- Objective 1: The complex dynamics of dislocations in plastic deformation of materials under imposed acoustic waves will be characterized using Concurrent Atomistic-Continuum (CAC) simulations. The atomistic and continuum level descriptions of the mechanical and dispersive transport behavior of materials will be unified using a statistical mechanics-based formulation
- Objective 2: To understand the evolution of local plasticity caused by the high-intensity acoustic waves, we will use time resolved nonlinear spectroscopy (TRNS), which is based on nonlinear resonant and wave phenomenon, to characterize the fast-time scale phenomenon. We will also carry-out SEM and Electron Backscatter Diffraction (EBSD) before and after the application of high intensity waves to resolve the slow-time scale. We will limit our focus to single and polycrystalline hexagonal-closed-packed (HCP) titanium and face-centered-cubic (FCC) copper.
- Objective 3: To bridge the multiple spatio-temporal scales, we will formulate a multiscale nonlinear parameter, which will be obtained from CAC and the experiments. The spatial and temporal bridging will allow us to capture the evolution of the mechanisms as a function time and frequency.
Intellectual merit: The proposed work aims to establish a fundamental understanding of the mechanics of acoustoplasticity from a multiscale perspective. Existing research uses continuum-level plasticity models, which work well for quasi-static phenomena but cannot resolve atomistic details of the elastic wave-dislocation interactions. The proposed research will fill these knowledge gaps by combining three techniques: multiscale simulations, in-situ TRNS, and SEM/EBSD, which will help us develop an understanding of acoustoplasticity across 6 orders of magnitude in time and length scales. The expected outcomes will be: (i) a series of atomistic-informed constitutive relations and kinetic rules that can be used in higher length scale computer models, such as crystal plasticity finite element, for meso-macroscopic scales; (ii) a quantitative understanding of the effect of acoustic amplitude, frequency, and dislocation characteristics on the acoustic softening behavior, and (iii) an understanding of the fundamental mechanics of acoustoplasticity from the atomistic to the continuum scale. Additionally, this proposal will end the long-standing debate on the role of the acoustic-induced temperature increase during acoustoplasticity by experimentally measuring the local temperature increase at an unprecedented spatial/temporal resolution and incorporating it into high-fidelity simulations.
Broader impacts: The combined computational-experimental framework will provide a bridge between fundamental research and applications of acoustoplasticity such as advanced manufacturing, structure health monitoring, and material characterization. In addition to graduate student training, the research generated from this work will be incorporated into courses at Michigan State University and Iowa State University. To facilitate broader dissemination, we will also introduce hands-on experimental workshops focusing on wave propagation, SEM, multiscale modeling phenomena targeting K-8 school children in the Lansing and Ames/Des Moines school districts. Student recruitment for graduate and undergraduate research assistants will focus on underrepresented minorities.
Composition-Processing-Microstructure-Property Relationships of the Zinc-Magnesium System for Absorbable Biomedical Implant Applications
The search for absorbable metal systems, showing a good combination of mechanical properties, uniform corrosion behavior, and biocompatibility, remains to be an open challenge. Magnesium (Mg) and zinc (Zn) have been identified as the most suitable elements to explore the next generation of biodegradable medical implant devices. However, none of the current Zn-Mg alloys is yet able to simultaneously meet those three benchmarks: adequate mechanical performance (i.e. tensile strength > 300 MPa, elongation-to-failure (
) > 20%) for structural support, biocompatibility to prevent an inflammatory response, and a corrosion rate matching that of the healing tissue.
Unlike conventional metal forming processes, i.e. rolling, forging, or extrusion, severe plastic deformation (SPD) techniques have shown potential to achieve a high strength while maintaining a good . In particular, Boehlert’s research group is focused on high-pressure torsion (HPT), as it is considered the most effective SPD technique in terms of grain refinement, and has been used for synthesizing new metal systems that can promote additional strengthening mechanisms. In collaboration with Professor Megumi Kawasaki of Oregon State University, Zn-Mg hybrid disks have been HPT-processed under 6 GPa applied pressure at room temperature (RT) under different conditions (1, 5, 15, and 30 turns) to evaluate their performance as potential absorbable biomedical candidates.
Composition-Processing-Microstructure-Property Relationships of Fe And Al Modified Ti-Cr Alloys
Beta-Titanium (Ti) alloys have applications in several industries (e.g. aerospace, automotive, and biomedical) where material performance requirements vary widely. Low-cost beta-Ti alloys, containing lower-cost alloying elements, are currently being investigated to help expand Ti alloy applications into industries where cost is prohibitive. Because the BCC beta phase is a metastable phase, it can undergo transformations to other metastable and stable phases which allow the microstructure and mechanical properties of beta-Ti alloys to be tailored to different applications. To control the microstructure of beta-Ti alloys, it is critical to understand the influence of individual alloying elements as well as the influence of processing conditions on the phase transformation in these alloys. Hardness testing, tensile testing, and resonance ultrasound spectroscopy have been used to investigate the mechanical properties of the alloys. Overall, a complete understanding of the composition-processing-microstructure-property relationships is being developed which can help further improvement of low-cost beta-Ti alloys.
To investigate the composition-processing-microstructure-property relationships of beta-Ti alloys, a low-cost Ti-Cr alloy system was chosen and modified using Fe and Al additions. Four alloy combinations were used to target the beta-to-omega and beta-to-alpha phase transformations: Ti-11Cr, Ti-11Cr-0.85Fe, Ti-11Cr-5.3Al, and Ti-11Cr-0.85Fe-5.3Al (all in at%). These alloys were subjected to 400C heat treatments for times between 0 and 24hrs and the phase transformations and mechanical properties of the alloys were investigated using multi-scale, multi-modal techniques. Scanning and transmission electron microscopy, high-temperature x-ray diffraction, and atom probe tomography techniques were used to determine the phase transformations and the diffusion of alloying elements occurring during the heat treatments. Needle specimens for atom probe tomography (APT) were prepared from the polished bulk metallographic samples by the focused ion beam (FIB)-based lift-out and annular milling method. To check this nanoscale compositional homogeneity of all four alloys, APT analysis was conducted. The ion maps in the Figure indicate that the element distribution in all four alloys was relatively uniform.
