Marc A. Meyers

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.

Thermomechcmical processing of Inconel 718 by shock-wave deformation

Abstract: The response of Inconel 718 nickel-base alloy to thermomechanical processing (TMP) utilizing a 510 Kbar planar shock wave was evaluated. The results were compared with those of conventional TMP by cold rolling to 19.1 pct reduction in thickness; this provided a generalized (or effective) strain equivalent to the transient shock strain. Instead of deformation in the solution treated condition, the inclusion of a predeformation, partial aging step in an optimized TMP schedule led to the greatest improvements in strength, stress-rupture life, and low-cycle fatigue life. The mechanical behavior was correlated with substructure and microstructure. Predeformation aging inhibits thermal recovery during final aging and produces a uniform dispersion of γ′’ precipitates. On a generalized (or effective) strain basis, conventional TMP by cold rolling produces higher strengths than shock TMP due to a higher dislocation density in the former. This suggests that maximum shear strain is a better basis of comparison. Since dislocation substructure is the primary contributor to property modification of Inconel 718 by TMP, the effective service temperature of thermomechanically processed material is limited to 1200°F (649°C), irrespective of the method of working.

Metallurgical and materials applications of shock-wave and high-strain-rate phenomena : proceedings of the 1995 International Conference on Metallurgical and Materials Applications of Shock-Wave and High-Strain-Rate Phenomena (EXPLOMET '95)

Abstract: Dynamic consolidation of materials dynamic fracture phenomena materials aspects of ballistic and hypervelocity impact and penetration extreme plastic deformation - adiabatic shear bands, dynamic recrystallization, shaped charges and explosively formed penetrators modelling and simulation of shock-wave and high-strain-rate phenomena in materials shock-induced reactions and synthesis shock-wave modification of materials structure and properties explosive welding, high-strain-rate deformation and material working.

Numerical modeling of the propagation of an adiabatic shear band

Abstract: The critical phenomena determining the propagation of an adiabatic shear band occur at its extremity. The stress and strain distributions at the tip of a shear band are calculated as a function of applied shear strain using the finite element method for an elasto-plastic material. Three assumptions simplify the calculations considerably: (a) the mechanical response of the material follows an adiabatic stress-strain curve; (b) the material within the shear band has zero shear strength; (c) the body is taken to be in equilibrium. The distribution of stresses and strains in the adiabatically-deformed material is compared to that of a quasi-statically deformed material. While the stress-strain curve for an isothermally deformed material is monotonic with continuous work-hardening, the adiabatic work-hardening curve reaches a plateau followed by work-softening (due to thermal softening). The stress and strain fields for both cases are nearly identical, except in the region directly in front of the shear band. In the adiabatically-deformed material a thin region (~5 μm) with large strains and lowered stresses is produced. This region, in which accelerated deformation takes place as the applied shear deformation increases, is absent in the isothermally-deformed material. The formation of this instability region, ahead of the shear band, is considered to be the mechanism for the propagation of an adiabatic shear band.

Fast parallel algorithms for short-range molecular dynamics

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.

Using Multivariate Statistics

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Phd by thesis

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

Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load

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.