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

The scaled boundary finite-element method—alias consistent infinitesimal finite-element cell method—for elastodynamics

Hybrid perovskite crystals are integrated onto silicon wafers enabling fabrication of an X-ray linear detector array. High sensitivity may reduce patient dose in medical imaging applications.

Monolithic integration of hybrid perovskite single crystals with heterogenous substrate for highly sensitive X-ray imaging

Hydrogen embrittlement in metals has posed a serious obstacle to designing strong and reliable structural materials for many decades, and predictive physical mechanisms still do not exist. Here, a new H embrittlement mechanism operating at the atomic scale in α-iron is demonstrated. Direct molecular dynamics simulations reveal a ductile-to-brittle transition caused by the suppression of dislocation emission at the crack tip due to aggregation of H, which then permits brittle-cleavage failure followed by slow crack growth. The atomistic embrittlement mechanism is then connected to material states and loading conditions through a kinetic model for H delivery to the crack-tip region. Parameter-free predictions of embrittlement thresholds in Fe-based steels over a range of H concentrations, mechanical loading rates and H diffusion rates are found to be in excellent agreement with experiments. This work provides a mechanistic, predictive framework for interpreting experiments, designing structural components and guiding the design of embrittlement-resistant materials.

Atomic mechanism and prediction of hydrogen embrittlement in iron

The effect of the adhesive thickness on the bond strength of single-lap adhesive joints is still not perfectly understood. The classical elastic analyses predict that the strength increases with the adhesive thickness, whereas experimental results show the opposite. Various theories have been proposed to explain this discrepancy, but more experimental tests are necessary to understand all the variables. The objective of the present study was to assess the effect of the adhesive thickness on the strength of single-lap joints for different kinds of adhesives. Three different adhesives were selected and tested in bulk. The strain to failure in tension ranged from 1.3% for the most brittle adhesive to 44% for the most ductile adhesive. The adherend selected was a high-strength steel to keep the adherends in the elastic range and simplify the analysis. Three thicknesses were studied for each adhesive: 0.2, 0.5, and 1 mm. A statistical analysis of the experimental results shows that the lap shear strength incre...

Effect of Adhesive Type and Thickness on the Lap Shear Strength

Solid particle erosion tests were carried out to study the effect of matrix materials, reinforcement fibers, interface strength between matrix material and fibers, im pact angle, and particle velocity on the solid particle erosion behavior of fiber reinforced plastics. In the present study, special attention was focused on the effect of the interface strength between matrix material and fibers, which has not been investigated in a lot of previous works related with the erosion of composite materials. FRPs with treated or un treated fiber surfaces were used as test materials to study the effect of interface strength be tween matrix material and fibers. It is found from the erosion tests that the erosion rate is larger in a FRP than in a neat resin, and that the erosion rate of a FRP decreases with the increase of the interface strength between matrix material and fibers.

Solid Particle Erosion of Fiber Reinforced Plastics

https://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/88963/1/j.actamat.2008.04.011.pdf

Atomistic study of hydrogen distribution and diffusion around a {112} edge dislocation in alpha iron

Experiments were carried out to study the effects of matrix materials, reinforcement fibers, impact angle and particle velocity on the solid particle erosion behavior of thermoplastic resins reinforced by short fibers. All of the previous research on the erosion of fiber-reinforced plastics deals with steady state erosion, and no work has been done on the initial process of erosion. So special attention was focussed on an incubation period of erosion. Two types of fiber-reinforced plastics were used for erosion tests. One was a new type of thermoplastic polyimide (New-TPI) resin reinforced by short glass or carbon fibers. The other was polyetheretherketone (PEEK) reinforced by short glass or carbon fibers. The fiber-reinforced plastics with different fiber contents were utilized as test materials to examine the effect of fiber content. Initial and eroded surfaces of test specimens were observed with a scanned electron microscope and an optical microscope. The results of the experiments show that the mass ...

Noriyuki Miyazaki

Papers

Solid Particle Erosion of Fiber Reinforced Plastics

Atomistic study of hydrogen distribution and diffusion around a {112} edge dislocation in alpha iron

Solid Particle Erosion of Thermoplastic Resins Reinforced by Short Fibers

Stress intensity factor analysis of interface crack using boundary element method (Application of contour-integral method)

Atomistic simulations of hydrogen embrittlement