Molecular dynamics simulations of compression–tension asymmetry in plasticity of Fe nanopillars

Tension-compression asymmetry is a notable feature of plasticity in bcc single crystals. Recent experiments reveal striking differences in the plasticity of bcc nanopillars for tension and compression. Here we present results from molecular dynamics simulations of nanopillars of bcc Fe in tension and compression. We find that a totally different deformation mechanism applies in each cases: dislocation glide in compression and twinning in tension. This difference explains experimentally-observed asymmetry in the nanopillar morphology

Investigation and Mechanical Modelling of Pure Molybdenum at High Strain-Rate and Temperature

This work shows the results obtained from the investigation of the mechanical behavior of two batches of pure molybdenum specimens (≥99.97 % Mo, Mo1 supplied by Plansee and Mo2 supplied by AT&M) under static and dynamic loading conditions at different temperatures, both under tensile and compressive loading conditions. Due to its properties molybdenum has applications in several fields including nuclear. At this moment, it is a good candidate for structural material application for Beam Intercepting Devices of the Large Hadron Collider at CERN, Geneva. The experimental tests in tensile loading condition were performed on small dog-bone specimens. A series of tests at room temperature and a range of strain-rates was performed in order to obtain information about the strain-rate sensitivity of the material. A series of tests at different temperatures in both static and high dynamic loading conditions was performed in order to obtain information about the thermal softening of the material. The dynamic tests were performed using the Hopkinson Bar technique, and the heating of the specimen was performed using an induction coil system. The experimental tests in compression were carried out on cylindrical specimens at room temperature and a range of strain-rates. The experimental data were analyzed via a numerical inverse method based on Finite Element numerical simulations. This approach allows to obtain the effective stress versus strain curves, which cannot be derived by using standard relations since instability and necking were present. Moreover, it also allows the non-uniform distribution of strain-rate and temperature inside the specimen to be accounted for. The results obtained from compression tests confirm the data obtained in tension in terms of strain-hardening and strain-rate sensitivity, even if the material exhibits a tension–compression asymmetry of the behavior. The analysis of the hardening, temperature and strain-rate sensitivities reveals that a unique standard visco-plastic model could not be defined to reproduce the material strength behavior under different loading conditions, especially over wide range of variation of the variables of interest

An Unconventional Pile-up Correction

The decay of valence satellite states in neon above the first double-ionization threshold has been studied experimentally and theoretically. Special emphasis was given to differentiate between two decay modes: valence Auger and valence-multiplet Auger decay. It is shown that the latter process is predominant in the low kinetic energy part of the spectrum. The main structures of this low-energy Auger spectrum could be designated by help of calculated transition energies and decay rates

Formation of micro shear bands during cyclic deformation of sub-microcrystalline nickel

Cyclic deformation of sub-microcrystalline nickel at high plastic strain amplitude generated macro shear bands, causing fatal cracking. The macro shear bands consisted of several micro shear bands, each band containing a single layer of elliptical grains that appeared at less than 50° with respect to the loading axis. Micro texture investigations in micro shear bands revealed almost the same texture with similar shear values as in macro shear bands. During cyclic deformation local overlapping of evolving micro shear bands resulted in formation of fatal macro shear bands