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Plastic deformations in body-centered-cubic (BCC) crystals have been of critical importance in diverse engineering and manufacturing contexts across length scales. Numerous experiments and atomistic simulations on BCC crystals reveal that classical crystal plasticity models with the Schmid law are not adequate to account for abnormal plastic deformations often found in these crystals. In this paper, we address a continuum mechanical treatment of anomalous plasticity in BCC crystals exhibiting non-Schmid effects, inspired from atomistic simulations recently reported. Specifically, anomalous features of plastic flows are addressed in conjunction with a single crystal constitutive model involving two non-Schmid projection tensors widely accepted for representing non-glide components of an applied stress tensor. Further, modeling results on a representative BCC single crystal (tantalum) are presented and compared to experimental data at a range of low temperatures to provide physical insight into deformation mechanisms in these crystals with non-Schmid effects.
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Molecular dynamics simulations were performed to understand the role of twin boundaries on deformation behaviour of body-centred cubic (BCC) iron (Fe) nanopillars. The twin boundaries varying from one to five providing twin boundary spacing in the range 8.5 - 2.8 nm were introduced perpendicular to the loading direction. The simulation results indicated that the twin boundaries in BCC Fe play a contrasting role during deformation under tensile and compressive loadings. During tensile deformation, a large reduction in yield stress was observed in twinned nanopillars compared to perfect nanopillar. However, the yield stress exhibited only marginal variation with respect to twin boundary spacing. On the contrary, a decrease in yield stress with increase in twin boundary spacing was obtained during compressive deformation. This contrasting behaviour originates from difference in operating mechanisms during yielding and subsequent plastic deformation. It has been observed that the deformation under tensile loading was dominated mainly by twin growth mechanism, due to which the twin boundaries offers a negligible resistance to slip of twinning partials. This is reflected in the negligible variation of yield stress as a function of twin boundary spacing. On the other hand, the deformation was dominated by nucleation and slip of full dislocations under compressive loading. The twin boundaries offer a strong repulsive force on full dislocations resulting in the yield stress dependence on twin boundary spacing. Further, it has been observed that the curved twin boundary can acts as a source for full dislocation. The occurrence of twin-twin interaction during tensile deformation and dislocation-twin interaction during compressive deformation were presented and discussed.
Radiation damage in body-centered cubic (BCC) Fe has been extensively studied by computer simulations to quantify effects of temperature, impinging particle energy, and the presence of extrinsic particles. However, limited investigation has been conducted into the effects of mechanical stresses and strain. In a reactor environment, structural materials are often mechanically strained, and an expanded understanding of how this strain affects the generation of defects may be important for predicting microstructural evolution and damage accumulation under such conditions. In this study, we have performed molecular dynamics simulations in which various types of homogeneous strains are applied to BCC Fe and the effect on defect generation is examined. It is found that volume-conserving shear strains yield no statistically significant variations in the stable number of defects created via cascades in BCC Fe. However, strains that result in volume changes are found to produce significant effects on defect generation.
Carbon, a basic versatile element in our universe, exhibits rich varieties of allotropic phases, most of which possess promising nontrivial topological fermions. In this work, we identify a distinct topological phonon phase in a realistic carbon allotrope with a body-centered cubic structure, termed bcc-C$_{8}$. We show by symmetry arguments and effective model analysis that there are three intersecting phonon nodal rings perpendicular to each other in different planes. The intersecting phonon nodal rings are protected by time-reversal and inversion symmetries, which quantize the corresponding Berry phase into integer multiples of $pi$. Unlike the electron systems, the phonon nodal rings in bcc-C$_{8}$ are guaranteed to remain gapless due to the lack of spin-orbital coupling. The nearly flat drumhead surface states projected on semi-infinite (001) and (110) surfaces of bcc-C$_{8}$ are clearly visible. Our findings not only discover promising nodal ring phonons in a carbon allotrope, but also provide emergent avenues for exploring topological phonons beyond fermionic electrons in carbon-allotropic structures with attractive features.
It is often computationally advantageous to model space as a discrete set of points forming a lattice grid. This technique is particularly useful for computationally difficult problems such as quantum many-body systems. For reasons of simplicity and familiarity, nearly all quantum many-body calculations have been performed on simple cubic lattices. Since the removal of lattice artifacts is often an important concern, it would be useful to perform calculations using more than one lattice geometry. In this work we show how to perform quantum many-body calculations using auxiliary-field Monte Carlo simulations on a three-dimensional body-centered cubic (BCC) lattice. As a benchmark test we compute the ground state energy of 33 spin-up and 33 spin-down fermions in the unitary limit, which is an idealized limit where the interaction range is zero and scattering length is infinite. As a fraction of the free Fermi gas energy $E_{rm FG}$, we find that the ground state energy is $E_0/E_{rm FG}= 0.369(2), 0.371(2),$ using two different definitions of the finite-system energy ratio. This is in excellent agreement with recent results obtained on a cubic lattice cite{He:2019ipt}. We find that the computational effort and performance on a BCC lattice is approximately the same as that for a cubic lattice with the same number of lattice points. We discuss how the lattice simulations with different geometries can be used to constrain the size lattice artifacts in simulations of continuum quantum many-body systems.
In this paper the elementary moves of the BFACF-algorithm for lattice polygons are generalised to elementary moves of BFACF-style algorithms for lattice polygons in the body-centred (BCC) and face-centred (FCC) cubic lattices. We prove that the ergodicity classes of these new elementary moves coincide with the knot types of unrooted polygons in the BCC and FCC lattices and so expand a similar result for the cubic lattice. Implementations of these algorithms for knotted polygons using the GAS algorithm produce estimates of the minimal length of knotted polygons in the BCC and FCC lattices.
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