There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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.

Fast parallel algorithms for short-range molecular dynamics

A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

https://zenodo.org/record/1258680/files/article.pdf

The influences of temperature and microstructure on the tensile properties of a CoCrFeMnNi high-entropy alloy

[Lu, K.; Lu, L.] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China. [Lu, L.; Suresh, S.] MIT, Sch Engn, Cambridge, MA 02139 USA.;Lu, K (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China;lu@imr.ac.cn ssuresh@mit.edu

/pdf/strengthening-materials-by-engineering-coherent-internal-4fkjmv3btq.pdf

Strengthening Materials by Engineering Coherent Internal Boundaries at the Nanoscale

In an effort to better understand the influence of impurities on the solid‐solid phase transitions in Group IVb metals, experiments have been carried out on polycrystalline zirconium samples using plate impact and isentropic loading techniques. Samples with three levels of impurities were shock‐loaded using both gas and powder‐driven guns and isentropically loaded using magnetic drive (Sandia’s Z‐Machine) to determine the properties and characteristics of both the α→ω and ω→β transitions.

/pdf/influence-of-impurities-on-the-solid-solid-phase-transitions-3ndhl8o4bc.pdf

Influence of Impurities on the Solid-Solid Phase Transitions in Zirconium

Post‐shock‐recovered metallurgical analysis of solid metal spheres shock loaded via spherical energetic(HE) loading provides a unique opportunity to quantify the substructure evolution in a material subjected to converging Taylor‐wave (triangular‐shock pulse) loading In this paper detailed quantitative metallographic, orientation‐imaging microscopy (OIM), and texture analysis is presented characterizing the gradient in substructure generated in Cu subjected to a spherical HE shock loading pulse at VNIIEF The substructure in the recovered sphere is seen to include: 1) a spherical cavity generated in the center of the sphere due to shock‐wave convergence and release, displaying ductile dimpled failure and no evidence of melting, 2) a gradient in deformation (slip and deformation twins) from the center outward to the surface, and 3) numerous shear cracks and/or spall planes The substructure evolution is discussed relative to that previously observed in Cu shock prestrained via either 1‐D triangular‐shaped shockwave loading or 1‐D square‐topped pulse shock loading

Substructure Evolution in Energetic‐Driven Spherically Shock‐Loaded Copper

Symposium on dynamic deformation: Constitutive modeling, grain size, and other effects-in honor of prof. Ronald W. Armstrong foreword

Several factors can affect the failure stress of a grain boundary, such as grain boundary structure, energy and excess volume, in addition to its interactions with dislocations. In this paper, we focus on the influence of grain boundary energy, excess volume and plasticity at the boundary on the failure stress of a grain boundary, in copper from molecular-dynamics simulations. Flyer plate simulations were carried out for four boundary types with different energies and excess volumes. These boundaries were chosen as model systems to represent various boundaries observed in real materials. Simulations indicate that there is no direct correlation between the void nucleation stress of a boundary and either its energy and excess volume. This result suggests that average properties of grain boundaries alone are not sufficient indicators of the failure strength of a boundary. However, local boundary properties related to the ability of a grain boundary to undergo plastic deformation are better markers of its strength.

https://iopscience.iop.org/article/10.1088/1742-6596/500/11/112024/pdf

Predicting failure stress for grain boundaries using average and local properties

Lateral stress gauges have been used to measure the variation of shear strength with longitudinal stress in shock loaded Ti‐6Al‐4V. Results show that lateral stress decreases slightly behind the shock front before reaching a constant level. We believe that this is due to the deformation microstructure not reaching its steady state immediately, but rather evolving over time. We have also observed that the Hugoniot and shear strength of our material is in close agreement to previous work. Recovered Taylor impact specimens show a circular foot print, and x‐ray tomography examination shows no evidence of tensile damage immediately under the impact face.

George T. Gray

Papers

Influence of Impurities on the Solid-Solid Phase Transitions in Zirconium

Substructure Evolution in Energetic‐Driven Spherically Shock‐Loaded Copper

Symposium on dynamic deformation: Constitutive modeling, grain size, and other effects-in honor of prof. Ronald W. Armstrong foreword

Predicting failure stress for grain boundaries using average and local properties

SHOCK LOADING AND TAYLOR IMPACT OF Ti‐6Al‐4V