Thanks to the following agencies for supporting our research!
Department of Defense (DOD), Army Research Office (ARO), Defense Advanced Research Projects Agency (DARPA), Air Force Office of Scientific Research (AFOSR), Army Research Lab (ARL), National Aeronautics and Space Administration (NASA), National Science Foundation (NSF), Nuclear Energy University Program (NEUP), Los Alamos National Laboratory (LEEG) funding, NEVADA NASA EPSCoR, IOWA NASA EPSCoR, NEVADA NASA Space Grant Consortium, IOWA Space Grant Consortium, ThinkSwiss, NAASIC (University of Nevada, Reno), Nevada EPSCoR.
About Our Research
Our Group is interested in the quantitative and qualitative measurement of materials behavior at lower(micron to sub-micron to nanometer) length scales over various material systems. Our research is focused on these main areas:
- Mechanistic Design of multilayered components
- Materials under extremes
Current Research Projects
Engineering Multilayered Metal-MAX phase Nanolaminate materials for tunable strength and toughness
Project member: Skye Supakul
Collaborators: Dr. Garritt Tucker, Colorado School of Mines.
Funding Agency: Army Research Office (ARO – W911NF1910389, Program Manager: Dr. Daniel P. Cole)
This project utilizes an integrated experimental (Iowa State University) and computational (Dr. Garritt Tucker, Colorado School of Mines) effort funded by the Army Research Office to engineer multilayered nanocomposite materials with unprecedented tunable strength and toughness. The nanocomposite is composed of alternating layers of metallic and MAX phase layers with lamellar thickness reduced to the nanoscale. Unique to other multilayered systems, the metal-MAX architecture detailed here is composed of a hierarchical topology with interfaces between the layers in direct competition with internal atomistic interfaces within the MAX layer to drive enhanced macroscopic mechanical behavior. Experimental synthesis and novel nanomechanical testing (i.e. nanoindentation, micropillar compression, and micro-tensile tension) performed at Iowa State University will look to quantify and qualify material properties and behaviors, providing experimental feedback for computational modeling and simulations developed by collaborators at the Colorado School of Mines investigating the interfacial structures and stability to elucidate the relationship between the hierarchical structure and improved mechanical properties.
|In-Situ Micro-Mechanical System for Testing of Advanced Materials under Extreme Conditions of Temperature, Strain-Rate and Applied Stress
Funding Agency: DURIP (ARO), Program Manager: Dr. Daniel P. Cole)
Testing under Extremes of Temperature and Strain-Rate
Understanding the Local Structure-Property Relationships of Pb-Sn Solders in Terrestrial vs. Microgravity Environments
Project member: Manish Kumar
Collaborators: NASA, Tec-Masters, Inc.
Funding Agency: NASA PSI, NASA EPSCoR
We have been awarded NASA PSI and NASA EPSCoR International Space Station (ISS) Flight Opportunity grant for “Structure and Properties of the Solder Joints Produced in Microgravity and Terrestrial environments.” This is collaborative work between the PI team at ISU, NASA researchers, and ISS implementation partners (Tec-Masters, Inc.).
This study compares solders prepared in terrestrial vs. microgravity (aboard the International Space Station, ISS) environments, 1g vs. ~1×10-5g. Using Pb-Sn solders from the In-Space Soldering Investigation (ISSI), we demonstrate how the lack of Earth’s natural convective flow and buoyancy effects during melting/solidification onboard ISS affects its microstructure and Properties, and performance. The understanding gained in this study will enable robust and reliable protocols for soldering-based solutions to address repair and fabrication needs for long-duration human exploration missions in (and beyond) low Earth orbit (ex: Moon, Mars).
Schematic of Gas Atomization Reaction Synthesis(GARS) setup.
|Direct Production of ODS Ferritic Alloys for Long-life Reactor Fuel Bundles: Sheet Material for Ducts and Tubing Pre-forms for Cladding
Project Member: Landon Hickman
Collaborators: Dr. Iver Anderson, Dr. Ralph Napolitano (Iowa State University), Dr. Jordon A Tiarks, Dr. Nicolas Argibay, Dr. Rameshwari Naorem ( Ames National Laboratory), Dr. Hyosim Kim (Los Alamos National Laboratory), Dr. Clinton Armstrong (Westinghouse Electric Company) and Dr. Stuart Maloy (Pacific Northwest National Laboratory)
Funding Agency: DOE-NEUP (Project Number – CFA-21-24729)
We seek to exploit the inherent uniformity, reasonable compressibility, and thermally-activated sintering of gas atomization reaction synthesis (GARS) precursor oxide dispersoid strengthened (ODS) ferritic steel powder to produce full density powder compacts by conventional vacuum warm pressing. Resulting billets will be cold cross-rolled to sheet material for duct applications. Hollow preforms, with a dissimilar powder core that can be readily removed, will be produced for cladding applications.
|Grain Interface Functional Design to Create Damage Resistance in Polycrystalline Metallic Materials
Project member: Olajesu Olanrewaju
Collaborators: Dr. Curt Bronkhorst, Dr. Nan Chen (University of Wisconsin, Madison), and Dr. Marko Knezevic (University of New Hampshire ).
Funding Agency: NSF DMREF (Award Number – 2118673, Program Manager: Dr. Siddiq Qidwai)
Even though polycrystalline metallic materials are ubiquitous in daily life, when and where metallic structural components damage and fail is difficult to predict, which generally leads to overdesign. This collaborative project addresses control of feature and defect character along with the internal stress state present for the manufacturing of polycrystalline metals against failure. Our group is responsible for material processing and sample preparation of a high-purity body-centered cubic tantalum, followed by micromechanical investigations, micro-pillar testing, and dynamic testing at the microscale. This project aims to design a manufacturing process to produce material that reduces damage by 30% over that in the as-received and annealed state.
|Small-scale Characterization of the Additive Manufactured Functional Hierarchical Shape Memory Alloy Structures
Project member: Deeksha Kodangal
Collaborators: Dr. Reginald Hamilton, Pennsylvania State University
Funding Agency: DARPA
This work focuses on the powder-fed AM technique- Laser Directed Energy Deposition (LDED) because of its inherent advantages when compared to the traditional route of producing Lamellar Shape Memory Alloy Structures (LSMAS). The AM LDED can be used for tailoring properties by controlling the elementally blended powder feedstock. The present work concentrates on understanding the anisotropy in the distribution in the precipitate morphology, grain texture and grain orientation along the LDED AM build height and build directions. The project aims to develop novel nano-/micro- scale test approaches that will establish the dependence of multi-scale deformation mechanisms on the differential microstructure length scales: precipitates and grains (nm-μm), AM layer/pass build plan (10-100 μm) and lamella of LSMAS (μm to mm). The interfaces between the build layers and between lamellae are in direct competition with the martensitic morphology and interactions with micro-constituents in the SMA to drive a tailored macroscopic mechanical behavior.
Biomechanics of Hierarchically-structured Hadrosaur Enamel in grinding dentitions
Project member: Dr. Soumya Verma
Collaborators: Dr. Brandon A Krick, Dr. Gregory M Erickson (Florida State University)
Funding Agency: AFOSR, NSF
This research aims to understand the biomechanical form, function, and structure of the enamel (a ceramic-like composite) known as aprismatic wavy enamel (WE) in the grinding dentition of large herbivores hadrosaurid dinosaurs. Our preliminary analysis of this tissue shows an undulating wavy structure in WE composed of folded layers of hydroxyapatite crystallites separated by thin layers of loosely aggregated interlayer matrix. This study specifically focuses on how the undulating wavy structure of this enamel helped dinosaurs’ teeth to deflect cracks and provided exceptional strength and toughness to mitigate the effects of fracture-promoting sediments while masticating.
Establishing processing-microstructure evolution linkages in polycrystalline metals
Our group’s research interests on nanomechanics addresses a critical need – that of deriving the precise relationships between microstructure and mechanical properties as the feature sizes of interest continue to decrease from micron to nanoscale dimensions. A major highlight is the development of novel data-analysis protocols for spherical nanoindentation, which allow meaningful spherical indentation stress-strain curves to be extracted from the raw datasets. This technique has now progressed into a field of its own where it is now possible to reliably estimate the entire indentation stress- strain response of a material at sub-micron length scales, starting from its initial elastic response and progressing all the way to its post-yield behavior. This enables coupling of the local mechanical response of a material, using spherical nanoindentation, with the structural information (see figure on left) obtained at the same length scale, thus paving the way for the successful development of physics-based multi-scale materials models at these lower dimensions. The versatility of this approach on a wide range of materials systems including metals, carbon nanotubes (CNTs), ceramics and biomaterials (bone) was published our 2015 invited review paper in Materials Science and Engineering: R.
Pathak S, Kalidindi SR. Spherical nanoindentation stress-strain curves. Materials Science and Engineering: R: Reports 2015;91:1-36
Furthermore, these techniques are of special advantage in studies of extreme environments, such as the study of mechanical degradation of irradiated materials (Fig), where nanoindentation shows the greatest promise due to its non-destructive nature, ease of experimentation (only a polished surface prior to ion irradiation is needed), high throughput and versatility. Our 2013 DOE-NEET and 2019 DOE Nuclear Energy University Program fellowship grants on this topic aims to combine the information obtained from spherical nanoindentation with different indenter sizes with structure characterization methods (e.g. EBSD) and physics-based finite element simulations of indentations to arrive at reliable estimates of the local properties.
|Mechanics and Materials Approach to Quantitative Assessment of Bone Quality
Beyond structural metals, our indentation stress-strain techniques have also enjoyed a fair degree of success in the study of micrometer and sub-micrometer sized domains in biological materials such as bone and enamel. Before the advent of such instrumented indentation methods, bone has been particularly challenging to characterize mechanically, especially at the micron length scales where the mineral and collagen components are closely intertwined. Our research in this field is aimed at to developing robust structure-property linkages in bone at each of its hierarchical levels of organization. Here we utilize tools such as quantitative backscattered electron microscopy (BSE-SEM), Fourier transform infra-red imaging (FTIR) and Raman vibrational spectroscopy to obtain the structure information at similar length scales. These projects will have the ambitious goal of assessing bone health and skeletal fragility, owing to age and disease related changes in the structure and morphology (quality and quantity) of bone, which is a growing problem in the United States and worldwide.
S. Pathak, J. Gregory Swadener, S. R. Kalidindi, H.-W. Courtland, K. J. Jepsen and H. M. Goldman,Journal of the Mechanical Behavior of Biomedical Materials,2011,4,34-43. S. Pathak, S. J. Vachhani, K. J. Jepsen, H. M. Goldman and S. R. Kalidindi,Journal of the Mechanical Behavior of Biomedical Materials,2012
|Collective Behavior of Vertically Aligned Carbon Nanotubes (VACNTs): from a Single Tube towards Complex Networks
In this work we explored the mechanical behavior of vertically aligned carbon nanotubes (VACNTs) also known as carbon nanotube (CNT) arrays, bundles, brushes, foams, forests, mats, and turfs. VACNTs are complex, hierarchical structures of intertwined tubes arrayed in a nominally vertical alignment due to their perpendicular growth from a stiff substrate. They are a unique class of materials having many of the desirable thermal, electrical, and mechanical properties of individual carbon nanotubes, while exhibiting these properties through the collective interaction of thousands of tubes on a macroscopic scale.
We investigated the synthesis techniques by which VACNTs are synthesized, which is the primary factor affecting their complex, hierarchical morphology. This microstructure, in turn, affects their mechanical behavior, in particular the modulus, buckling strength, and recoverability. Using nanomechanical testing techniques, we compared the mechanical response of VACNTs under different loading conditions, namely compression and indentation. We analyzed the resultant large variation in structure and properties of VACNTs (porosity, CNT tube thickness, modulus, buckling strength), their large scale deformation and buckling behavior, viscoelasticity and potential applications.