scholarly journals Mechanical Properties of Silk: Interplay of Deformation on Macroscopic and Molecular Length Scales

2008 ◽  
Vol 100 (4) ◽  
Author(s):  
Igor Krasnov ◽  
Imke Diddens ◽  
Nadine Hauptmann ◽  
Gesa Helms ◽  
Malte Ogurreck ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Length Scales ◽  
Molecular Length

scholarly journals Modelling and Experimentation on Mechanical Properties of Graphene-Oxide Cement

2019 ◽  
Vol 274 ◽  
pp. 05004
Author(s):  
Zhiyuan Lin ◽  
Ding Fan ◽  
Shangtong Yang
Keyword(s):  
Mechanical Properties ◽  
Graphene Oxide ◽  
Elastic Properties ◽  
High Surface ◽  
High Surface Area ◽  
Accurate Estimation ◽  
Dispersion Property ◽  
Length Scales ◽  
Analysis And Design ◽  
Strength And Durability

Cementitious nano-composites have recently attracted considerable research interest in order to improve their properties such as strength and durability. Graphene oxide (GO) is being considered as an ideal candidate for enhancing the mechanical properties of the cement due to its good dispersion property and high surface area. Much of work has been done on experimentally investigating the mechanical properties of GO-cementitious composites; but there are currently no models for accurate estimation of their mechanical properties, making proper analysis and design of GO-cement based materials a major challenge. This paper attempts to develop a novel multi-scale analytical model for predicting the elastic modulus of GO-cement taking into account the GO/cement ratio, porosity and mechanical properties of different phases. This model employs Eshelby tensor and Mori-Tanaka solution in the process of upscaling the elastic properties of GO-cement through different length scales. In-situ micro bending tests were conducted to elucidate the behavior of the GO-cement composites and verify the proposed model. The obtained results showed that the addition of GO can change the morphology and enhance the mechanical properties of the cement. The developed model can be used as a tool to determine the elastic properties of GO-cement through different length scales.

scholarly journals Fuel Cell Electrode Characterization Using Neutron Scattering

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1474 ◽  
Author(s):  
Olaf Holderer ◽  
Marcelo Carmo ◽  
Meital Shviro ◽  
Werner Lehnert ◽  
Yohei Noda ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Large Scale ◽  
Proton Mobility ◽  
Length Scales ◽  
Fuel Cell Electrode ◽  
Molecular Length ◽  
Energy Conversion And Storage ◽  
Ion Conducting ◽  
Cell Electrode ◽  
The Individual

Electrochemical energy conversion and storage is key for the use of regenerative energies at large scale. A thorough understanding of the individual components, such as the ion conducting membrane and the electrode layers, can be obtained with scattering techniques on atomic to molecular length scales. The largely heterogeneous electrode layers of High-Temperature Polymer Electrolyte Fuel Cells are studied in this work with small- and wide-angle neutron scattering at the same time with the iMATERIA diffractometer at the spallation neutron source at J-PARC, opening a view on structural properties on atomic to mesoscopic length scales. Recent results on the proton mobility from the same samples measured with backscattering spectroscopy are put into relation with the structural findings.

Effect of Moisture and Graded-Layer Mechanical Properties on Deformation and Interfacial Adhesion

2003 ◽  
Vol 778 ◽  
Author(s):  
Lorraine C. Wang ◽  
Reinhold H. Dauskardt
Keyword(s):  
Mechanical Properties ◽  
Layer Thickness ◽  
Material Properties ◽  
Interface Fracture ◽  
Material Structure ◽  
Second Phase ◽  
Length Scales ◽  
Adhesion Properties ◽  
Micron Size ◽  
Thermal And Electrical Properties

AbstractControlling material properties over nanometer length scales is crucial for current and emerging high-density microelectronic device packages. Miniaturization of devices is increasingly limited by the ability to “connect” to the device, and the required packaging structures must be fabricated where layer thickness and feature sizes approach micron size scales while achieving the required mechanical, thermal and electrical properties. Second phase additions such as sub-micron sized particles are often added to locally adjust the material properties of constituent layers in the complex package structure. This results in significant variation of mechanical properties over sub-micron length scales. Such manipulation of material structure and its effects on mechanical and interfacial fracture behavior are addressed using experimental and modeling studies. Underfill layers consisting of an epoxy matrix with dispersed silica beads are shown to exhibit variations of elastic and flow properties in excess of three-fold across the layer thickness. Mechanical properties are not only affected by the distribution of second-phase fillers, but also by the adhesion properties of the filler/matrix interface. Interfaces are susceptible to stress corrosion cracking associated with moisture which can lead to progressive debond growth at loads much lower than that required to exceed the critical interface fracture energies. Subcritical debonding is affected by temperature, humidity, and the bond chemistry of the interface. The effects of these variations are considered on the adhesive and subcritical debonding behavior of interfaces between model epoxy underfills and SiNx chip passivation. Implications for other constrained complex layered structures are considered.

Molecular Structure and Rubberlike Elasticity. III. Molecular Movements in Rubberlike Polymers

1942 ◽  
Vol 15 (4) ◽  
pp. 742-755 ◽  
Author(s):  
C. W. Bunn
Keyword(s):  
Mechanical Properties ◽  
Crystallization Temperature ◽  
X Ray Diffraction ◽  
Single Chain ◽  
Trans Form ◽  
Gutta Percha ◽  
Molecular Movement ◽  
Molecular Behavior ◽  
Molecular Length ◽  
The Difference

Abstract In Part I of this work, the crystal structures of β-gutta-percha, rubber and polychloroprene (deduced from x-ray diffraction photographs) were described. In pursuance of the idea that rubberlike properties are due to molecular flexibility which result from the swivelling of the chain units around single chain bonds, it is necessary to consider which chain-bond positions are the most stable and what hindrances there are to rotation away from these positions. The question of the most stable bond positions was considered in Part II. I now consider the evidence for the occurrence of rotation in rubberlike substances, the hindrances to rotation in different molecules, their effect on the crystallization or melting temperature, and the explanation of the mechanical properties of these substances in terms of structure and molecular movement, both above and below the crystallization temperature. Rubber is noncrystalline and elastic at room temperature; but on cooling below 0° C it crystallizes, and in that condition has the mechanical properties of gutta-percha; i.e., a frozen specimen no longer has enormous elasticity, but it can be drawn or rolled out irreversibly, whereby the crystals become oriented. Conversely, if gutta-percha is wanned to 70° C, it becomes amorphous (transparent, optically isotropic and noncrystalline), and its mechanical properties are then like those of rubber—it is soft and elastic. The difference between the two substances thus appears to be essentially a difference of crystallization temperature. These crystallization temperatures are remarkably low; e.g., polyethylene, (—CH2—CH2—)n, of comparable molecular length, crystallizes at 115–125° C. In attempting to understand rubberlike elasticity in terms of molecular behavior, the first question is why are the crystallization points of such enormous molecules so low, and why is the crystallization point of the cis-form of polyisoprene (rubber) lower than that of the trans-form (gutta-percha).

scholarly journals Understanding the paradoxical mechanical response of in-phase A-tracts at different force regimes

2019 ◽  
Author(s):  
Alberto Marin-Gonzalez ◽  
Cesar L. Pastrana ◽  
Rebeca Bocanegra ◽  
Alejandro Martín-González ◽  
J.G. Vilhena ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Optical Tweezers ◽  
Single Molecule ◽  
Dna Sequences ◽  
Mechanical Response ◽  
Magnetic Tweezers ◽  
Crystallographic Structure ◽  
Chain Model ◽  
Microscopy Imaging ◽  
Length Scales

ABSTRACTA-tracts are A:T rich DNA sequences that exhibit unique structural and mechanical properties associated with several functions in vivo. The crystallographic structure of A-tracts has been well characterized. However, their response to forces remains unknown and the variability of their flexibility reported for different length scales has precluded a comprehensive description of the mechanical properties of these molecules. Here, we rationalize the mechanical properties of A-tracts across multiple length scales using a combination of single-molecule experiments and theoretical polymer models applied to DNA sequences present in the C. elegans genome. Atomic Force Microscopy imaging shows that phased A-tracts induce long-range (∼200 nm) bending. Moreover, the enhanced bending originates from an intrinsically bent structure rather than as a consequence of larger flexibility. In support of this, our data were well described with a theoretical model based on the worm-like chain model that includes intrinsic bending. Magnetic tweezers experiments confirm that the observed bent is intrinsic to the sequence and does not rely on particular ionic conditions. Using optical tweezers, we assess the local rigidity of A-tracts at high forces and unravel an unusually stiff character of these sequences, as quantified by their large stretch modulus. Our work rationalizes the complex multiscale flexibility of A-tracts, shedding light on the cryptic character of these sequences.

Hydration effects on the micro-mechanical properties of bone

2006 ◽  
Vol 21 (8) ◽  
pp. 1962-1968 ◽  
Author(s):  
A.K. Bembey ◽  
A.J. Bushby ◽  
A. Boyde ◽  
V.L. Ferguson ◽  
M.L. Oyen
Keyword(s):  
Physical Chemistry ◽  
Mechanical Properties ◽  
Composite Material ◽  
Bathing Solution ◽  
Creep Tests ◽  
Length Scales ◽  
Mechanical Integrity ◽  
Tissue Hydration ◽  
Mechanical Responses ◽  
Hydration State

Bone is a composite material with hydroxyapatite mineral, collagen, and water as primary components. Water plays an important role in maintaining the mechanical integrity of the composite, but the manner in which water interacts within the collagen and mineral at ultrastructural length-scales is poorly understood. The current study examined changes in the mechanical properties of bone as a function of hydration state. Tissues were soaked in different solvents and solutions, with different polarities, to manipulate tissue hydration. Mineralized bone was characterized using nanoindentation creep tests for quantification of both the elastic and viscoelastic mechanical responses, which varied dramatically with tissue bathing solution. The results were considered within the context of solution physical chemistry. Selectively removing and then replacing water provided insights into the ultrastructure of the tissues via the corresponding changes in the experimentally determined mechanical responses.

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