Author
Marc A. Meyers
Other affiliations: University of California, Instituto Militar de Engenharia, University of Denver ...read more
Bio: Marc A. Meyers is an academic researcher from University of California, San Diego. The author has contributed to research in topics: Deformation (engineering) & Dislocation. The author has an hindex of 85, co-authored 487 publications receiving 36646 citations. Previous affiliations of Marc A. Meyers include University of California & Instituto Militar de Engenharia.
Papers published on a yearly basis
Papers
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TL;DR: In this paper, molecular dynamics simulations are used to systematically investigate the effect of size and concentration of He bubbles in Cu with planar free surfaces on ejecta production, and it is shown that the presence of defects leads to the formation of non-planarity in the shock wave itself producing ejecta as the front reaches the flat free surface.
Abstract: The interaction of shock waves with non-planar free surfaces can cause atoms to eject from the surface, leading to the formation of ejecta. These non-planarities in the free surface can occur due to machining of the free surface or can be induced in the shock wave itself due to the presence of heterogeneities in the material. Both cases lead to the formation of ejecta. While the effect of machining on ejecta has been well studied, the latter has not been a topic of significant investigations. In this work, molecular dynamics simulations are used to systematically investigate the effect of size and concentration of He bubbles in Cu with planar free surfaces on ejecta production. It is shown that the presence of defects leads to the formation of non-planarity in the shock wave itself producing ejecta as the front reaches the flat free surface. The cluster size and velocity of ejected particles greatly exceeds that of pure Cu; the radius, density, and nature of the helium-filled voids alter the mass, velocity, and size distribution of the ejected matter.
4 citations
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TL;DR: The formation of bandes de cisaillement is studied in this article, where it is shown that the deformation is inhomogene, and that the distance entre les bandes and l'epaisseur des bandes are plus faibles for le carbure de silicium granule.
Abstract: Des echantillons de carbure de silicium pre-fragmentes et granulaires ont ete soumis a des hautes deformations a hautes vitesses par l'implosion symetrique d'un cylindre a parois epaisses. La formation de bandes de cisaillement a ete observee, indiquant que la deformation est inhomogene. Le cisaillement dans les bandes, la distance entre les bandes et l'epaisseur des bandes etaient plus faibles pour le carbure de silicium granule. Une distribution de taille de poudre bimodale a ete observee dans les bandes pour les deux materiaux. La formation de bandes de cisaillement a ete produite principalement par la fragmentation des poudres et la reorganisation des particules pulverisees. Les bandes de cisaillement dans le materiau pre-fissure sont formees par l'addition de fragments a partir des interfaces de la bande de cisaillement et par l'erosion des fragments a l'interieur de la bande de cisaillement.
4 citations
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29 Mar 2012
TL;DR: In this paper, the growth and collapse of nanoscale voids in tantalum are investigated under different stress states and strain rates by molecular dynamics simulations and three principal mechanisms of deformation are identified and quantitatively evaluated: shear loop emission, prismatic loop formation, and twinning.
Abstract: Shock-induced spall in ductile metals is known to occur by the sequence of nucleation, growth and coalescence of voids, even in high purity monocrystals. However, the atomistic mechanisms involved are still not completely understood. The growth and collapse of nanoscale voids in tantalum are investigated under different stress states and strain rates by molecular dynamics (MD) simulations. Three principal mechanisms of deformation are identified and quantitatively evaluated: shear loop emission, prismatic loop formation, and twinning. Dislocation shear loops expand as expected from a crystallographic analysis, and their extremities remain attached to the void surface in tension (if there is no dislocation reaction or cross slip), but can detach in compression and form prismatic loops due to cross slip and reactions. Prismatic loops that detach from the void are also formed by reaction of multiple shear loops sharing the same <111< slip direction during hydrostatic loading. Nanotwins form preferably upon both uniaxial and hydrostatic tensile stress. The void-size effect on plasticity is studied via MD simulations and is modeled based on the shear loop emission mechanism. The stresses required for generation of a free surface step, dislocation and bow are calculated by continuum dislocation theory. The predictions agree well with MD simulation results.
4 citations
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TL;DR: The Arapaima fish scales are composed of two layers: a laminate composite of parallel collagen fibrils arranged in a Bouligand-like pattern, and a hard, highly mineralized surface layer that prevents initial penetration damage as mentioned in this paper.
Abstract: In order for fish scales to provide protection from predators without significantly compromising mobility, they have to be lightweight, flexible and tough. The Arapaima fish scale is a superb example of these properties, which enable survival in piranha-infested seasonal lakes of the Amazon. These elasmoid scales are composed of two layers: a laminate composite of parallel collagen fibrils arranged in a Bouligand-like pattern, and a hard, highly mineralized surface layer that prevents initial penetration damage. We measure here the J-integral based fracture toughness of the scale and find that the crack-growth toughness as high as ~200 kJ⋅m-2, representing a very high fracture resistance for a flexible biological material. This toughness is primarily the result of multiple mechanisms of deformation acting in concert in the twisted plywood structure of the scale, involving the collagen lamellae at varying orientations controlling crack advance through stretching, rotation, delamination and shear, and finally fracture. These toughening mechanisms operate in sequence at the crack tip, retarding its advance in a most effective manner. The toughness values obtained for the Arapaima scales indicate that they are among the toughest of nature’s flexible biological materials.
4 citations
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01 May 1993
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.
Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.
29,323 citations
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28,685 citations
01 Jan 2016
TL;DR: The using multivariate statistics is universally compatible with any devices to read, allowing you to get the most less latency time to download any of the authors' books like this one.
Abstract: Thank you for downloading using multivariate statistics. As you may know, people have look hundreds times for their favorite novels like this using multivariate statistics, but end up in infectious downloads. Rather than reading a good book with a cup of tea in the afternoon, instead they juggled with some harmful bugs inside their laptop. using multivariate statistics is available in our digital library an online access to it is set as public so you can download it instantly. Our books collection saves in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Merely said, the using multivariate statistics is universally compatible with any devices to read.
14,604 citations
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TL;DR: In this paper, a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) is presented.
Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These
9,929 citations
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TL;DR: The tensile strengths of individual multiwalled carbon nanotubes (MWCNTs) were measured with a "nanostressing stage" located within a scanning electron microscope and a variety of structures were revealed, such as a nanotube ribbon, a wave pattern, and partial radial collapse.
Abstract: The tensile strengths of individual multiwalled carbon nanotubes (MWCNTs) were measured with a “nanostressing stage” located within a scanning electron microscope. The tensile-loading experiment was prepared and observed entirely within the microscope and was recorded on video. The MWCNTs broke in the outermost layer (“sword-in-sheath” failure), and the tensile strength of this layer ranged from 11 to 63 gigapascals for the set of 19 MWCNTs that were loaded. Analysis of the stress-strain curves for individual MWCNTs indicated that the Young's modulus E of the outermost layer varied from 270 to 950 gigapascals. Transmission electron microscopic examination of the broken nanotube fragments revealed a variety of structures, such as a nanotube ribbon, a wave pattern, and partial radial collapse.
5,011 citations