Magnesium-rich nanoprecipitates in calcite: atomistic mechanisms responsible for toughening in Ophiocoma wendtii

AbstractWe have carried out a series of atomistic simulations on arrays of about 10,000 atoms containing an atomically sharp crack and subjected to increasing stress levels. The ordered stoichiometric alloys B2 NiAl, B2 RuAl and A15 Nb3AI have been studied at different temperatures and stress levels, as well as the elements Al, Ni, Nb and Ru. The many body interactions used in the simulations were derived semi-empirically, using techniques related to the Embedded Atom Method. Trends in dislocation generation rates and crack propagation modes will be discussed and compared to experimental indications where possible, and some of the simulations will be demonstrated in the form of computer movies.

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Molecular photoswitches mediating the strain-driven disassembly of supramolecular tubules

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1711184114 ◽

2017 ◽

Vol 114 (45) ◽

pp. 11850-11855 ◽

Cited By ~ 39

Author(s):

Jean W. Fredy ◽

Alejandro Méndez-Ardoy ◽

Supaporn Kwangmettatam ◽

Davide Bochicchio ◽

Benjamin Matt ◽

...

Keyword(s):

Essential Feature ◽

Operation Mode ◽

Building Blocks ◽

Water Soluble ◽

Atomistic Simulations ◽

Supramolecular Architecture ◽

Mechanical Responses ◽

Pulling Forces ◽

Nonlinear Operation ◽

Insight Into

Chemists have created molecular machines and switches with specific mechanical responses that were typically demonstrated in solution, where mechanically relevant motion is dissipated in the Brownian storm. The next challenge consists of designing specific mechanisms through which the action of individual molecules is transmitted to a supramolecular architecture, with a sense of directionality. Cellular microtubules are capable of meeting such a challenge. While their capacity to generate pushing forces by ratcheting growth is well known, conversely these versatile machines can also pull microscopic objects apart through a burst of their rigid tubular structure. One essential feature of this disassembling mechanism is the accumulation of strain in the tubules, which develops when tubulin dimers change shape, triggered by a hydrolysis event. We envision a strategy toward supramolecular machines generating directional pulling forces by harnessing the mechanically purposeful motion of molecular switches in supramolecular tubules. Here, we report on wholly synthetic, water-soluble, and chiral tubules that incorporate photoswitchable building blocks in their supramolecular architecture. Under illumination, these tubules display a nonlinear operation mode, by which light is transformed into units of strain by the shape changes of individual switches, until a threshold is reached and the tubules unleash the strain energy. The operation of this wholly synthetic and stripped-down system compares to the conformational wave by which cellular microtubules disassemble. Additionally, atomistic simulations provide molecular insight into how strain accumulates to induce destabilization. Our findings pave the way toward supramolecular machines that would photogenerate pulling forces, at the nanoscale and beyond.

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Crack propagation speeds in weak snowpack layers

Journal of Glaciology ◽

10.1017/jog.2021.118 ◽

2021 ◽

pp. 1-14

Author(s):

Bastian Bergfeld ◽

Alec van Herwijnen ◽

Grégoire Bobillier ◽

Eric Larose ◽

Ludovic Moreau ◽

...

Keyword(s):

Crack Propagation ◽

Elastic Waves ◽

Scale Up ◽

Element Model ◽

Material Point ◽

Flexural Wave ◽

Crack Speed ◽

The Mean ◽

Underlying Processes ◽

Insight Into

Abstract For the release of a slab avalanche, crack propagation within a weak snowpack layer below a cohesive snow slab is required. As crack speed measurements can give insight into underlying processes, we analysed three crack propagation events that occurred in similar snowpacks and covered all scales relevant for avalanche release. For the largest scale, up to 400 m, we estimated crack speed from an avalanche movie; for scales between 5 and 25 m, we used accelerometers placed on the snow surface and for scales below 5 m, we performed a propagation saw test. The mean crack speeds ranged from 36 ± 6 to 49 ± 5 m s−1, and did not exhibit scale dependence. Using the discrete element method and the material point method, we reproduced the measured crack speeds reasonably well, in particular the terminal crack speed observed at smaller scales. Finally, we used a finite element model to assess the speed of different elastic waves in a layered snowpack. Results suggest that the observed cracks propagated as mixed mode closing cracks and that the flexural wave of the slab is responsible for the energy transfer to the crack tip.

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Dynamic crack propagation in weak snowpack layers: Insights from high-resolution, high-speed photography

10.5194/tc-2020-360 ◽

2021 ◽

Author(s):

Bastian Bergfeld ◽

Alec van Herwijnen ◽

Benjamin Reuter ◽

Grégoire Bobillier ◽

Jürg Dual ◽

...

Keyword(s):

High Resolution ◽

Crack Propagation ◽

Fracture Energy ◽

High Speed ◽

Image Correlation ◽

Crack Speed ◽

Specific Fracture Energy ◽

Weak Layer ◽

Specific Fracture ◽

Insight Into

Abstract. To assess snow avalanche release probability, information on failure initiation and crack propagation in weak snowpack layers underlying cohesive slab layers are required. With the introduction of the Propagation Saw Test (PST) in the mid-2000s, various studies used particle tracking analysis of high-speed video recordings of PST experiments to gain insight into crack propagation processes, including slab bending, weak layer collapse, crack propagation speed and the frictional behavior after weak layer fracture. However, the resolution of the videos and the methodology used did not allow insight into dynamic processes such as the evolution of crack speed within a PST or the touchdown distance, which is the length from the crack tip to the trailing point where the slab sits on the crushed weak layer at rest again. Therefore, to study the dynamics of crack propagation we recorded PST experiments using a powerful portable high-speed camera with a horizontal resolution of 1280 pixels at rates up to 20,000 frames per second. By applying a high-density speckling pattern on the entire PST column, we then used digital image correlation (DIC) to derive high-resolution displacement and strain fields in the slab, weak layer, and substrate. The high frame rates allowed time derivatives to obtain velocity and acceleration fields. On the one hand, we demonstrate the versatile capabilities and accuracy of the DIC method by showing three PST experiments resulting in slab fracture, crack arrest and full propagation. On the other hand, we present a methodology to determine relevant characteristics of crack propagation: the crack speed and touchdown distance within a PST, and the specific fracture energy of the weak layer. To estimate the effective elastic modulus of the slab and weak layer as well as the weak layer specific fracture energy we used a recently proposed mechanical model. A comparison to already established methods showed good agreement. Furthermore, our methodology also provides insight into the three different propagation results found with the PST and reveals intricate dynamics that are otherwise not accessible.

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Molecular determinants and bottlenecks in the unbinding dynamics of biotin-streptavidin

10.1101/176594 ◽

2017 ◽

Author(s):

Pratyush Tiwary

Keyword(s):

Atomistic Simulations ◽

Enhanced Sampling ◽

Protein Ligand Interactions ◽

Direct Benefits ◽

Molecular Determinants ◽

Bond Stretching ◽

Ligand Interactions ◽

Non Covalent Interactions ◽

Covalent Interactions ◽

Insight Into

Biotin-streptavidin is a very popular system used to gain insight into protein-ligand interactions. In its tetrameric form, it is well-known for its extremely long residence times, being one of the strongest known non-covalent interactions in nature, and is heavily used across the biotechnological industry. In this work we gain understanding into the molecular determinants and bottlenecks in the unbinding of the dimeric biotinstreptavidin system in its wild type and with N23A mutation. Using new enhanced sampling methods with full atomistic resolution, we reproduce the variation caused by N23A mutation in experimentally reported residence time. We also answer a longstanding question regarding cause/effect in the coupled events of bond stretching and bond hydration during unbinding and establish that in this system, it is the bond stretching and not hydration which forms the bottleneck in the early parts of the unbinding. We believe these calculations represent a step forward in the use of atomistic simulations to study pharmacodynamics. An improved understanding of biotin-streptavidin unbinding dynamics should also have direct benefits in biotechnological and nanobiotechnological applications.

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Atomistic Simulations of Mechanics of Nanostructures

MRS Bulletin ◽

10.1557/mrs2009.46 ◽

2009 ◽

Vol 34 (3) ◽

pp. 160-166 ◽

Cited By ~ 15

Author(s):

Hanchen Huang ◽

Helena Van Swygenhoven

Keyword(s):

Deformation Mechanism ◽

Bulk Material ◽

Atomistic Simulations ◽

Ideal Strength ◽

Electronic Level ◽

Nanostructure Materials ◽

Common Features ◽

Surfaces And Interfaces ◽

Insight Into

AbstractNanostructures can be in the form of nanoparticles or nanograins, nanowires or nanotubes, and nanoplates or multilayers. These nanostructures may be used individually or embedded in a bulk material. In both cases, they share two common features. First, the small dimensions minimize or even eliminate the presence of defects. Second, nanostructures entail large surface or interface areas. The absence of defects makes nanostructure materials stronger than their bulk counterparts, leading to the eventual realization of ideal strength. The presence of surfaces and interfaces may either reduce or increase the strength. Atomistic simulations can provide insight into the deformation mechanism at the atomic and electronic level, something that is very difficult to obtain from experiments. This article describes generic features of nanostructures and summarizes the five areas presented in the articles in this issue.

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Atomistic Study of Crack Propagation and Dislocation Emission in Cu-Ni Multilayers

MRS Proceedings ◽

10.1557/proc-457-315 ◽

1996 ◽

Vol 457 ◽

Cited By ~ 2

Author(s):

Jeff Clinedinst ◽

Diana Farkas

Keyword(s):

Crack Propagation ◽

Mechanical Behavior ◽

Coherent Structure ◽

Atomistic Simulations ◽

Crack Plane ◽

Dislocation Emission ◽

Molecular Statics ◽

Atomistic Study ◽

Atomistic Structure ◽

Interface Effects

ABSTRACTWe present atomistic simulations of the crack tip configuration in multilayered Cu-Ni materials. The simulations were carried out using molecular statics and EAM potentials. The atomistic structure of the interface was studied first for a totally coherent structure. Cracks were simulated near a Griffith condition in different possible configurations of the crack plane and front with respect to the axis of the layers. Results show that interface effects predominately control the mechanical behavior of the system studied.

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Multiscale modeling of solids at the nanoscale: dynamic approach

Canadian Journal of Physics ◽

10.1139/p07-145 ◽

2008 ◽

Vol 86 (2) ◽

pp. 391-400 ◽

Cited By ~ 7

Author(s):

B Shiari ◽

R E Miller ◽

D D Klug

Keyword(s):

Computational Cost ◽

Atomistic Simulations ◽

Process Variables ◽

Dynamic Approach ◽

Multiscale Models ◽

Major Class ◽

Dislocation Plasticity ◽

System Temperature ◽

Cyclic Indentation ◽

Insight Into

One major class of multiscale models directly couples a region described with full atomistic detail to a surrounding region modeled using continuum concepts and finite element methods. Here, the development of a new dynamic approach to such coupled atomistic-continuum models is discussed with insight into the key ideas and features, with emphasis on fundamental difficulties involved in dynamic multiscale models. Simulations of nanoindentation in single crystals are performed to demonstrate the power of the developed method in capturing both long-range dislocation plasticity and short-range atomistic phenomena during single or cyclic loading without the computational cost of full atomistic simulations. The effects of several process variables are investigated, including system temperature and rate of indentation. The deformation mechanisms and the surface evaluation that occur during a series of single and cyclic indentation simulations are discussed. PACS Nos.: 81.07.–b or 73.22.–f

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