scholarly journals Heterogeneous origami-architected materials with variable stiffness

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Yasuhiro Miyazawa ◽  
Hiromi Yasuda ◽  
Hyungkyu Kim ◽  
James H. Lynch ◽  
Kosei Tsujikawa ◽  
...  
Keyword(s):  
Variable Stiffness ◽  
Mechanical Stiffness ◽  
Paper Folding ◽  
Shannon Information Entropy ◽  
Unit Cells ◽  
Analysis Strategy ◽  
Mechanical Devices ◽  
Reconfigurable Structures ◽  
Identical Unit

AbstractOrigami, the ancient art of paper folding, has shown its potential as a versatile platform to design various reconfigurable structures. The designs of most origami-inspired architected materials rely on a periodic arrangement of identical unit cells repeated throughout the whole system. It is challenging to alter the arrangement once the design is fixed, which may limit the reconfigurable nature of origami-based structures. Inspired by phase transformations in natural materials, here we study origami tessellations that can transform between homogeneous configurations and highly heterogeneous configurations composed of different phases of origami unit cells. We find that extremely localized and reprogrammable heterogeneity can be achieved in our origami tessellation, which enables the control of mechanical stiffness and in-situ tunable locking behavior. To analyze this high reconfigurability and variable stiffness systematically, we employ Shannon information entropy. Our design and analysis strategy can pave the way for designing new types of transformable mechanical devices.

Measurement and Reduction of Radiation Damage in Frozen Hydrated Crystalline Specimens

1978 ◽  
Vol 36 (3) ◽  
pp. 70-77 ◽  
Author(s):  
R.M. Glaeser ◽  
S.B. Hayward
Keyword(s):  
Diffraction Pattern ◽  
Structural Information ◽  
Structural Disorder ◽  
Structural Features ◽  
Biological Macromolecules ◽  
Diffraction Intensity ◽  
Object Structure ◽  
Specimen Material ◽  
Unit Cells ◽  
Identical Unit

Highly ordered or crystalline biological macromolecules become severely damaged and structurally disordered after a brief electron exposure. Evidence that damage and structural disorder are occurring is clearly given by the fading and eventual disappearance of the specimen's electron diffraction pattern. The fading and disappearance of sharp diffraction spots implies a corresponding disappearance of periodic structural features in the specimen. By the same token, there is a oneto- one correspondence between the disappearance of the crystalline diffraction pattern and the disappearance of reproducible structural information that can be observed in the images of identical unit cells of the object structure. The electron exposures that result in a significant decrease in the diffraction intensity will depend somewhat upon the resolution (Bragg spacing) involved, and can vary considerably with the chemical makeup and composition of the specimen material.

scholarly journals Incidence, Risk, and Visual Outcomes after Repositioning of Acute Non-Traumatic Flap Dislocations Following Femtosecond-Assisted LASIK

2021 ◽  
Vol 10 (11) ◽  
pp. 2478
Author(s):  
Majid Moshirfar ◽  
David G. West ◽  
Chase M Miller ◽  
William B. West ◽  
Shannon E. McCabe ◽  
...  
Keyword(s):  
Risk Factors ◽  
Visual Acuity ◽  
High Myopia ◽  
Case Series ◽  
Retrospective Case ◽  
Visual Outcomes ◽  
Uncorrected Distance Visual Acuity ◽  
Incidence Risk ◽  
Mechanical Devices

Although the use of femtosecond lasers instead of mechanical devices has decreased the incidence of flap complications following laser-assisted in situ keratomileusis (LASIK), dislocations and striae still occur. Flap repositioning is an effective intervention to improve visual outcomes after acute flap complications in both microkeratome-assisted and femtosecond-assisted LASIK. This retrospective case series included patients undergoing flap repositioning secondary to acute flap dislocation and/or visually significant striae within the first two weeks following femtosecond LASIK (FS-LASIK) from 2015 to 2020 at a single institution. Preoperative, intraoperative, and postoperative de-identified data were analyzed for incidence, risk factors, and visual acuity outcomes. The incidence of flap repositioning was 0.35% in 21,536 eyes (n = 70). Indications for repositioning included acute flap dislocation (35.7%) and visually significant striae (64.3%). High myopia (OR = 3.04, p = 0.001) and patient age over 50 years (OR = 3.69, p = 0.001) were the strongest risk factors for these complications. Prior to flap repositioning, uncorrected distance visual acuity (UDVA) of 20/20 or better and 20/40 or better occurred in 19% and 57% of eyes, respectively. After repositioning, a final UDVA of 20/20 or better and 20/40 or better occurred in 78% and 98% of eyes, respectively. After repositioning, one line of UDVA was lost in two eyes (2.8%) and two lines were lost in one eye (1.4%). Risk factors for acute flap dislocation included high myopia and age over 50 years. Flap repositioning was effective in salvaging visual outcomes.

scholarly journals The Interaction Features of the Multi-Level Retaining Walls with Soil Mass

2017 ◽  
Vol 26 (3) ◽  
pp. 179-190
Author(s):  
Igor Boyko ◽  
Liudmyla Skochko ◽  
Veronica Zhuk
Keyword(s):  
Numerical Modelling ◽  
Numerical Simulations ◽  
Variable Stiffness ◽  
Retaining Walls ◽  
Soil Mass ◽  
Soil Base ◽  
Deep Foundation ◽  
Multi Level ◽  
Horizontal Displacements

Abstract The interaction features of multi-level retaining walls with soil base were researched by changing their geometric parameters and locality at the plan. During excavation of deep foundation pits it is important to choose the type of constructions which influences on the horizontal displacements. The distance between the levels of retaining walls should be based on the results of numerical modelling. The objective of this paper is to present a comparison between the data of numerical simulations and the results of the in-situ lateral tests of couple piles. The problems have been solved by using the following soil models: Coulomb-Mohr model; model, which is based on the dilatation theory; elastic-plastic model with variable stiffness parameters.

scholarly journals Swelling-induced wrinkling in layered gel beams

2017 ◽  
Vol 473 (2207) ◽  
pp. 20170454 ◽  
Author(s):  
P. Nardinocchi ◽  
E. Puntel
Keyword(s):  
Perturbation Analysis ◽  
Biomedical Applications ◽  
Finite Strain ◽  
Parameter Plane ◽  
Linear Perturbation ◽  
Stiffness Ratio ◽  
Height Ratio ◽  
Mechanical Stiffness ◽  
Total Height ◽  
Mechanical Devices

Gels are widely employed in smart mechanical devices and biomedical applications. Swelling-induced bending actuation can be obtained by means of a simple bilayer gel beam. We show that this system can also exhibit wrinkling patterns of potential interest for structural morphing and sensing. We study swelling-induced wrinkling at the extrados of a bilayer gel beam with the softer layer on top. The bent configuration at finite strain is recovered first and, starting from it, a linear perturbation analysis is performed. We delimit the zone corresponding to wrinkling modes in a parameter plane encompassing a mechanical stiffness ratio and a geometric top layer to total height ratio. Interestingly, we observe that surface instability precedes and envelopes wrinkling modes of finite wavelength. Finally, we discuss the effect of changes in stiffness and of the Flory–Huggins parameters χ on the size of the wrinkling domain.

scholarly journals Processing and Characterization of Silicon Nitride Nanofiber Paper

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Kei-Peng Jen ◽  
Ronald Warzoha ◽  
Ji Guo ◽  
Michael Tang ◽  
Sridhar Santhanam
Keyword(s):  
Silicon Nitride ◽  
Thermal Insulation ◽  
Reduction Process ◽  
Thermal Characterization ◽  
Nitride Phase ◽  
Mechanical Stiffness ◽  
Precursor Material ◽  
Processing Step

Papers of silicon nitride nanofibers were synthesized by a carbothermal reduction process. These nanofiber papers were synthesized in situ and did not require a secondary processing step. The process utilized silica nanopowders and silica gel as the precursor material. Processing geometry played a crucial role in regulating the growth of the nanofiber papers. Characterization of the nanofiber papers indicated that the nanofibers were of the alpha silicon nitride phase. Both mechanical stiffness and strength of the nanofiber papers were measured. Thermal conductivity and specific heat of the papers were also measured and were found to be lower than many common thermal insulation materials at much smaller thicknesses and were comparable to those values that are typically reported for carbon-nanotube-based buckypaper. Results of the mechanical and thermal characterization indicate that these silicon nitride nanofiber papers can be utilized for specialized thermal insulation applications.

scholarly journals In Situ Monitoring of Growth of Vertically Stacked h-BN/Graphene Heterostructures on Ni Substrates and Their Interface Interaction

Surfaces ◽  
2020 ◽  
Vol 3 (3) ◽  
pp. 328-336
Author(s):  
Wei Wei ◽  
Guanhua Zhang ◽  
Jiaqi Pan ◽  
Yi Cui ◽  
Qiang Fu
Keyword(s):  
Hexagonal Boron Nitride ◽  
Chemical Vapor ◽  
In Situ Monitoring ◽  
High Coverage ◽  
Interface Interaction ◽  
Domain Boundaries ◽  
Potential Applications ◽  
Surface Microscopy ◽  
Mechanical Devices

Vertically stacked hexagonal boron nitride (h-BN)/graphene heterostructures present potential applications in electronic, photonic, and mechanical devices, and their interface interaction is one of the critical factors that affect the performances. In this work, the vertical h-BN/graphene heterostructures with high coverage are synthesized by chemical vapor deposition (CVD) of h-BN on Ni substrates followed by segregation growth of graphene at the h-BN/Ni interfaces, which are monitored by in situ surface microscopy and surface spectroscopy. We find that h-BN overlayers can be decoupled from Ni substrates by the graphene interlayers. Furthermore, the h-BN domain boundaries exhibit a confinement effect on the graphene interlayer growth and the lower graphene domains are limited within the upper h-BN domains. This work provides new insights into the formation mechanism and interface interaction of the vertical heterostructures.

scholarly journals In Situ Electric-Field Study of Surface Effects in Domain Engineered Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 Relaxor Crystals by Grazing Incidence Diffraction

Crystals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 728
Author(s):  
Markys G. Cain ◽  
Margo Staruch ◽  
Paul Thompson ◽  
Christopher Lucas ◽  
Didier Wermeille ◽  
...  
Keyword(s):  
Electric Field ◽  
Crystal Surface ◽  
Grazing Incidence ◽  
Sample Surface ◽  
X Ray Diffraction ◽  
Near Surface ◽  
Unit Cells ◽  
Lattice Planes ◽  
Sweet Spots

In this work, we present a grazing incidence X-ray diffraction study of the surface of a 0.24Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) [011] poled rhombohedral single crystal. The near surface microstructure (the top several tens to hundreds of unit cells) was measured in situ under an applied electric field. The strains calculated from the change in lattice parameters have been compared to the macroscopic strain measured with a strain gauge affixed to the sample surface. The depth dependence of the electrostrain at the crystal surface was investigated as a function of temperature. The analysis revealed hidden sweet spots featuring unusually high strains that were observed as a function of depth, temperature and orientation of the lattice planes.

scholarly journals Nanostructured Metal Hydrides for Hydrogen Storage Studied by In Situ Synchrotron and Neutron Diffraction

2010 ◽  
Vol 1262 ◽  
Author(s):  
Volodymyr Yartys ◽  
Roman Denys ◽  
Jan Petter Maehlen ◽  
Colin J Webb ◽  
Evan MacA Gray ◽  
...  
Keyword(s):  
Hydrogen Storage ◽  
Hydrogen Exchange ◽  
High Pressures ◽  
Storage Systems ◽  
Time Resolved ◽  
Fast Kinetics ◽  
Al Content ◽  
Unit Cells ◽  
Complementary Techniques

AbstractThis work was focused on studies of the metal hydride materials having a potential in building hydrogen storage systems with high gravimetric and volumetric efficiencies of H storage and formed / decomposed with high rates of hydrogen exchange. In situ diffraction studies of the metal-hydrogen systems were explored as a valuable tool in probing both the mechanism of the phase-structural transformations and their kinetics. Two complementary techniques, namely Neutron Powder Diffraction (NPD) and Synchrotron X-ray diffraction (SR XRD) were utilised. High pressure in situ NPD studies were performed at D2 pressures reaching 1000 bar at the D1B diffractometer accommodated at Institute Laue Langevin, Grenoble. The data of the time resolved in situ SR XRD were collected at the Swiss Norwegian Beam Lines, ESRF, Grenoble in the pressure range up to 50 bar H2 at temperatures 20-400°C.The systems studied by NPD at high pressures included deuterated Al-modified Laves-type C15 ZrFe2-xAlx intermetallics with x = 0.02; 0.04 and 0.20 and the CeNi5-D2 system. D content, hysteresis of H uptake and release, unit cell expansion and stability of the hydrides systematically change with Al content.Deuteration exhibited a very fast kinetics; it resulted in increase of the unit cells volumes reaching 23.5 % for ZrFe1.98Al0.02D2.9(1) and associated with exclusive occupancy of the Zr2(Fe,Al)2 tetrahedra.For CeNi5 deuteration yielded a hexahydride CeNi5D6.2 (20°C, 776 bar D2) and was accompanied by a nearly isotropic volume expansion reaching 30.1% (∆a/a=10.0%; ∆c/c=7.5%). Deuterium atoms fill three different interstitial sites including Ce2Ni2, Ce2Ni3 and Ni4. Significant hysteresis was observed on the first absorption-desorption cycle. This hysteresis decreased on the absorption-desorption cycling.A different approach to the development of H storage systems is based on the hydrides of light elements, first of all the Mg-based ones. These systems were studied by SR XRD. Reactive ball milling in hydrogen (HRBM) allowed synthesis of the nanostructured Mg-based hydrides.The experimental parameters (PH2, T, energy of milling, ball / sample ratio and balls size), significantly influence rate of hydrogenation. The studies confirmed (a) a completeness of hydrogenation of Mg into MgH2; (b) indicated a partial transformation of the originally formed -MgH2 into a metastable -MgH2 (a ratio / was 3/1); (c) yielded the crystallite size for the main hydrogenation product, -MgH2, as close to 10 nm. Influence of the additives to Mg on the structure and hydrogen absorption/desorption properties and cycle behaviour of the composites was established and will be discussed in the paper.

Design, Manufacturing and Testing of an In-situ Consolidated Variable Stiffness Thermoplastic Composite Wingbox for Bending and Torsion

2019 ◽  
Author(s):  
VINCENZO OLIVERI ◽  
GIOVANNI ZUCCO ◽  
DANIËL PEETERS ◽  
GEARÒID CLANCY ◽  
ROBERT TELFORD ◽  
...  
Keyword(s):  
Variable Stiffness ◽  
Thermoplastic Composite

Failure Surfaces for Finitely Strained Two-Phase Periodic Solids Under General In-Plane Loading

2005 ◽  
Vol 73 (3) ◽  
pp. 505-515 ◽  
Author(s):  
N. Triantafyllidis ◽  
M. D. Nestorović ◽  
M. W. Schraad
Keyword(s):  
Variable Stiffness ◽  
Bloch Wave ◽  
Two Phase ◽  
Buckling Mode ◽  
Unit Cells ◽  
First Occurrence ◽  
Order Of Magnitude ◽  
Ultimate Failure ◽  
Periodic Microstructures ◽  
Strain Space

For ductile solids with periodic microstructures (e.g., honeycombs, fiber-reinforced composites, cellular solids) which are loaded primarily in compression, their ultimate failure is related to the onset of a buckling mode. Consequently, for periodic solids of infinite extent, one can define as the onset of failure the first occurrence of a bifurcation in the fundamental solution, for which all cells deform identically. By following all possible loading paths in strain or stress space, one can construct onset-of-failure surfaces for finitely strained, rate-independent solids with arbitrary microstructures. The calculations required are based on a Bloch wave analysis on the deformed unit cell. The presentation of the general theory is followed by the description of a numerical algorithm which reduces the size of stability matrices by an order of magnitude, thus improving the computational efficiency for the case of continuum unit cells. The theory is subsequently applied to porous and particle-reinforced hyperelastic solids with circular inclusions of variable stiffness. The corresponding failure surfaces in strain-space, the wavelength of the instabilities, and their dependence on micro-geometry and macroscopic loading conditions are presented and discussed.

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