skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.
Attention:The NSF Public Access Repository (PAR) system and access will be unavailable from 11:00 PM ET on Thursday, May 14 until 2:00 AM ET on Friday, May 15 due to maintenance. We apologize for the inconvenience.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Opening-Dominated Fracture Characterization of Single Crystal Spinel in the Transmission Electron Microscope
Abstract BackgroundCharacterizing deformation and failure mechanisms through small-scale testing has helped in the fundamental understanding of material response, and direct loading in a transmission electron microscope (TEM) has played a large role in this effort. However, crystalline materials exhibit incoherent scattering within the TEM and the resulting intensity variations inhibit direct optical metrology. ObjectiveIn this work, we seek to both validate anin situoptical full-field metrology method in the TEM for use with crystalline materials, and measure fracture properties of a MgAl2O4spinel single crystal at the microscale. MethodsMicroscale single edge notch bend beams were machined from a spinel single crystal and loaded in the TEM.In situimaging of a nanoscale speckle pattern allowed use of particle tracking (PT) to extract full-field measurements of the displacement field. A numerical analysis methodology was then used to obtain mixed mode stress intensity factor values. ResultsA discrepancy between PT and far-field actuator measurements of applied displacement was found (about a maximum of 35% difference), indicating the advantage of using near-field optical measurements in the TEM. For such small-scale testing it is also generally unavoidable to introduce asymmetry in loading. However, the PT results allowed measurement of bothKIandKII, which were found to be at the time of crack initiationKIC= 1.51± 0.03 MPa∙m0.5, KIIC= 0.04± 0.002 MPa∙m0.5, respectively. ConclusionsThe application of PT enables full-field deformation measurements on crystalline materials deformed in the TEM. The effectiveness of the inverse property extraction was demonstrated by good agreement between the full-field PT measurements and FEM results. The MgAl2O4spinel toughness values extracted also agreed well with previous literature results.  more » « less
Award ID(s):
1825466
PAR ID:
10674860
Author(s) / Creator(s):
; ;
Publisher / Repository:
Springer
Date Published:
Journal Name:
Experimental Mechanics
Volume:
66
Issue:
1
ISSN:
0014-4851
Page Range / eLocation ID:
153 to 162
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; (, Journal of the American Ceramic Society)
    ABSTRACT In this work, failure of a magnesium aluminate spinel (MgAl2O4) is investigated at the microscale by concurrent in situ imaging and loading within a transmission electron microscope. The goal of the effort is to quantitively measure the grain boundary fracture toughness of a spinel bi‐crystal and study the toughness property disparity between the grain boundary and lattice (measured in an earlier effort). Additionally, the mode mixity dependence of the grain boundary fracture properties is measured as the applied loading configuration is varied. By placing a notch aligned with the grain boundary at the top or bottom edge of a bi‐crystal beam sample, bending experiments can generate grain boundary failure with different mode mixites. Critical energy release rates and mode mixity indicators for each sample were extracted through three‐dimensional finite element analysis (FEA), validated by comparison of particle tracking measurements with the FEA results. For opening‐dominated fracture, the grain boundary exhibited a lower fracture energy when compared to the single crystal lattice. Alternatively, shear‐dominated modes exhibit much larger toughness. 
    more » « less
  2. ; ; ; ; ; ; ; (, Applied Microbiology and Biotechnology)
    de Leon, Lester (Ed.)
    AbstractRecently, we reported the discovery of a novel endoglucanase of the glycoside hydrolase family 12 (GH12), designated IfCelS12A, from the haloalkaliphilic anaerobic bacteriumIocasia fonsfrigidaestrain SP3-1, which was isolated from a hypersaline pond in the Samut Sakhon province of Thailand (ca. 2017). IfCelS12A exhibits high substrate specificity on carboxymethyl cellulose and amorphous cellulose but low substrate specificity on b-1,3;1,4-glucan. Unlike some endoglucanases of the GH12 family, IfCelS12A does not exhibit hydrolytic activity on crystalline cellulose (i.e., Avicel™). High-Pressure Liquid Chromatography (HPLC) and Thin Layer Chromatography (TLC) analyses of products resulting from IfCelS12-mediated hydrolysis indicate mode of action for this enzyme. Notably, IfCelS12A preferentially hydrolyzes cellotetraoses, cellopentaoses, and cellohexaoses with negligible activity on cellobiose or cellotriose. Kinetic analysis with cellopentaose and barely b-d-glucan as cellulosic substrates were conducted. On cellopentaose, IfCelS12A demonstrates a 16-fold increase in activity (KM = 0.27 mM;kcat = 0.36 s−1;kcat/KM = 1.34 mM−1s−1) compared to the enzymatic hydrolysis of barley b-d-glucan (KM: 0.04 mM,kcat: 0.51 s−1,kcat/KM = 0.08 mM−1s−1). Moreover, IfCelS12A enzymatic efficacy is stable in hypersaline sodium chlorids (NaCl) solutions (up to 10% NaCl). Specifically, IfCel12A retains notable activity after 24 h at 2M NaCl (10% saline solution). IfCelS12A used as a cocktail component with other cellulolytic enzymes and in conjunction with mobile sequestration platform technology offers additional options for deconstruction of ionic liquid–pretreated cellulosic feedstock. Key points•IfCelS12A from an anaerobic alkaliphile Iocasia fronsfrigidae shows salt tolerance•IfCelS12A in cocktails with other enzymes efficiently degrades cellulosic biomass•IfCelS12A used with mobile enzyme sequestration platforms enhances hydrolysis 
    more » « less
  3. ; ; ; ; ; ; (, Materials Research Express)
    Abstract Hypergolic reactions have emerged as a new synthetic approach enabling the rapid production of a diverse set of materials at ambient conditions. While hypergolic reactions bear several similarities to the well-established flame spray pyrolysis (FSP), the former has only recently been demonstrated as a viable approach to materials synthesis. Here we demonstrate a new pathway to 2D materials using hypergolic reactions and expand the gallery of nanomaterials synthesized hypergolically. More specifically, we demonstrate that ammonia borane complex, NH3BH3, or 4-fluoroaniline can react hypergolically with fuming nitric acid to form hexagonal boron nitride/fluorinated carbon nanosheets, respectively. Structural and chemical features were confirmed with x-ray diffraction, infrared, Raman, XPS spectroscopies and N2porosimetry measurements. Electron microscopy (SEM and TEM) along with atomic force microscopy (AFM) were used to characterize the morphology of the materials. Finally, we applied Hansen affinity parameters to quantify the surface/interfacial properties using their dispersibility in solvents. Of the solvents tested, ethylene glycol and ethanol exhibited the most stable dispersions of hexagonal boron nitride (h-BN). With respect to fluorinated carbon (FC) nanosheets, the suitable solvents for high stability dispersions were dimethylsulfoxide and 2-propanol. The dispersibility was quantified in terms of Hansen affinity parameters (δd,δp,δh) = (16.6, 8.2, 21.3) and (17.4, 10.1, 14.5) MPa1/2for h-BN and FC, respectively. 
    more » « less
  4. ; ; ; ; ; ; (, Communications Materials)
    Abstract Kagome materials are of topical interest for their diverse quantum properties linked with correlated magnetism and topology. Here, we report anomalous hydrostatic pressure (p) effect on ErMn6Sn6through isobaric and isothermal-isobaric magnetization measurements. Magnetic field (H) suppresses antiferromagneticTNwhile simultaneously enhancing the ferrimagneticTCby exhibiting dual metamagnetic transitions, arising from the triple-spiral-nature of Er and Mn spins. Counter-intuitively, pressure enhances bothTCandTNwith a growth rate of 74.4 K GPa−1and 14.4 K GPa−1respectively. Pressure unifies the dual metamagnetic transitions as illustrated throughp-Hphase diagrams at 140 and 200 K. Temperature-field-pressure (T-H,T-p) phase diagrams illustrate distinct field- and pressure-induced critical points at (Tcr= 246 K,Hcr= 23.3 kOe) and (Tcr= 435.8 K,pcr= 4.74 GPa) respectively. An unusual increase of magnetic entropy by pressure aroundTcrand a putative pressure-induced tricritical point pave a unique way of tuning the magnetic properties of kagome magnets through simultaneous application ofHandp. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Advanced Materials)
    Abstract Achieving substantial electrostrain alongside a large effective piezoelectric strain coefficient (d33*) in piezoelectric materials remains a formidable challenge for advanced actuator applications. Here, a straightforward approach to enhance these properties by strategically designing the domain structure and controlling the domain switching through the introduction of arrays of ordered {100}<100> dislocations is proposed. This dislocation engineering yields an intrinsic lock‐in steady–state electrostrain of 0.69% at a low field of 10 kV cm−1without external stress and an output strain energy density of 5.24 J cm−3in single‐crystal BaTiO3, outperforming the benchmark piezoceramics and relaxor ferroelectric single‐crystals. Additionally, applying a compression stress of 6 MPa fully unlocks electrostrains exceeding 1%, yielding a remarkabled33* value over 10 000 pm V−1and achieving a record‐high strain energy density of 11.67 J cm−3. Optical and transmission electron microscopy, paired with laboratory and synchrotron X‐ray diffraction, is employed to rationalize the observed electrostrain. Phase‐field simulations further elucidate the impact of charged dislocations on domain nucleation and domain switching. These findings present an effective and sustainable strategy for developing high‐performance, lead‐free piezoelectric materials without the need for additional chemical elements, offering immense potential for actuator technologies. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email