Shigenobu Ogata 교수

Although aluminum has a smaller modulus in [111]<112> shear than that of copper, we find by first-principles calculation that its ideal shear strength is larger because of a more extended deformation range before softening. This fundamental behavior, along with an abnormally high intrinsic stacking fault energy and a different orientation dependence on pressure hardening, are traced to the directional nature of its bonding. By a comparative analysis of ion relaxations and valence charge redistri

Using density functional theory we analyze the stress-strain responses of 22 simple metals and ceramics to determine the maximum shear strain a homogeneous crystal can withstand, a property for which we suggest the name shearability. A shearability gap is found between metals and covalent ceramics. Shearability of metals further correlates with the degree of valence charge localization and directional bonding. Depending on the deformation constraints, ionic solids may possess even larger shearab

Energy landscapes of $(2\overline{1}\overline{1})⟨111⟩$ deformation twinning in bcc Mo and $(111)⟨11\overline{2}⟩$ deformation twinning in fcc Al and Cu are determined using density functional theory for sliding of layers numbering up to 7. In bcc Mo, the minimum thickness of a metastable twin is two layers, while twin embryos of three and four layers are unstable. Starting from five layers, the Mo twin can grow in a layer-by-layer fashion. The twin boundary formation and migration energies are

The ideal tensile (compressive) strength, Young's modulus, and band-gap changes of single-walled carbon nanotubes (SWNT's) with zigzag types of (8,0), (9,0), and (10,0) and armchair of (8,8) under an uniaxial deformation are analyzed using a tight binding (TB) method parametrized by Tang et al. In addition, the first principle density functional theory based on the local density approximation (DFT) is employed as a cross-check. It is well known that the band gap of a SWNT changes according to th

First-principles studies on the intrinsic mechanical properties of various materials and systems through ab initio tensile and shear testing simulations based on density-functional theory are reviewed. For various materials, ideal tensile and shear strength and features of the deformation of bulk crystals without any defects have been examined, and the relation with the bonding nature has been analyzed. The surfaces or low-dimensional nano-structures reveal peculiar strength and deformation beha

Abstract Rejuvenation is the structural excitation of glassy materials, and is a promising approach for improving the macroscopic deformability of metallic glasses. This atomistic study proposes the application of compressive hydrostatic pressure during the glass-forming quenching process and demonstrates highly rejuvenated glass states that have not been attainable without the application of pressure. Surprisingly, the pressure-promoted rejuvenation process increases the characteristic short- a

We correlate the experimentally measured fracture toughness of 24 metals and ceramics to their quantum mechanically calculated brittleness parameter. The brittleness parameter is defined as the ratio of the elastic energy density needed to spontaneously break bonds in shear versus in tension, and is a primitive-cell property. Under 300 GPa hydrostatic pressure, the model predicts that diamond has smaller brittleness than molybdenum at zero pressure, and thus should deform plastically without cra