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On the structure of a new superhard hexagonal carbon phase ; ; et al in AIP Conference Proceedings (2010), 1233(PART 1), 489-493 Molecular dynamics simulations show that graphite will transform into a superhard phase under cold compression. Recent experiments show that there is a sp 3-rich hexagonal carbon polymorph (a 0=2.496 Å, c ... [more ▼] Molecular dynamics simulations show that graphite will transform into a superhard phase under cold compression. Recent experiments show that there is a sp 3-rich hexagonal carbon polymorph (a 0=2.496 Å, c 0=4.123Å) with a bulk modulus of 447 GPa and average density about 3.6g/cm 3, restricted to the space group of P-62c (No. 190), but the detailed atomic structure was not obtained [Wang et al., P. Natl. Acad. Sci. 101(38), 13699]. Here we set carbon atoms occupying P-62c 4f Wyckoff positions of P-62c, and calculate the total energy of the different structures changing the internal parameter z by first-principles calculations using geometry optimisation algorithm in CASTEP code, which shows that the stable structures in energy (at local minimum points) are hexagonal carbon (z=1/4) and hexagonal diamond (z=1/16). The calculated mechanical properties and lattice parameters of the structure P-62c 4f (z=1/4) are in good agreement with those of the new hexagonal carbon proposed by Wang et al., which indicates that the atomic structure is a possible candidate. © 2010 American Institute of Physics. [less ▲] Detailed reference viewed: 49 (0 UL)An element nodal force-based large increment method for elastoplasticity ; ; et al in AIP Conference Proceedings (2010), 1233(PART 1), 1401-1405 This paper presents a new method for establishing the basic equations in the novel force-based large increment method (LIM) for continuum elastoplastic problems. In LIM, unlike traditional displacement ... [more ▼] This paper presents a new method for establishing the basic equations in the novel force-based large increment method (LIM) for continuum elastoplastic problems. In LIM, unlike traditional displacement methods, the (generalised) elemental force variables are adopted as system unknowns. The equilibrium equations can then be obtained directly at every nodal degree of freedom without physical equations (i.e., constitutive equations) involved. The generalised inverse of the non-square system of equations is employed to obtain the set of solutions of the non-square matrix equations directly. A conjugate gradient procedure is then used to find the correct solution from this set of solutions by optimising the compatibility of the solution based on the fact that the correct solution should also satisfy the constitutive equations and the compatibility equations. In this paper, the generalised elemental force variables are defined based on the element nodal forces. The LIM framework is therefore successfully applied to elements based on this definition. The efficiency and accuracy of the LIM are illustrated with a few benchmark problems and the results are compared with the analytical solution and the conventional displacement-based finite element method. [less ▲] Detailed reference viewed: 47 (0 UL)On the Smoothed eXtended Finite Element Method for Continuum ; Bordas, Stéphane ; et al Scientific Conference (2009, April) In this paper, we combine the strain smoothing technique proposed by Liu et al [1] coined as the smoothed finite element method (SFEM) to partition of unity methods, namely the extended finite element ... [more ▼] In this paper, we combine the strain smoothing technique proposed by Liu et al [1] coined as the smoothed finite element method (SFEM) to partition of unity methods, namely the extended finite element method (XFEM) [2] to give birth to the smoothed extended finite element method (SmXFEM) [3]. SmXFEM shares properties both with the SFEM and the XFEM. The proposed method eliminates the need to compute and integrate the derivatives of shape functions (which are singular at the tip for linear elastic fracture mechanics). The need for isoparametric mapping is eliminated because the integration is done along the boundary of the finite element or smoothing cells, which allows elements of arbitrary shape. We present numerical results for various differential equations that have singularity or steep gradient at the boundary. The method is verified on several examples and comparisons are made to the conventional XFEM. [less ▲] Detailed reference viewed: 91 (1 UL)A novel numerical integration technique over arbitrary polygons ; ; Bordas, Stéphane et al Scientific Conference (2009, April) In this paper, a new numerical integration technique [1] on arbitrary polygons is presented. The polygonal do- main is mapped conformally to the unit disk using Schwarz-Christoffel mapping [2] and a ... [more ▼] In this paper, a new numerical integration technique [1] on arbitrary polygons is presented. The polygonal do- main is mapped conformally to the unit disk using Schwarz-Christoffel mapping [2] and a midpoint quadrature rule defined on the unit circle is used. This method eliminates the need for a two level isoparametric mapping usuall required [3]. Moreover the positivity of the Jacobian is guaranteed. We present numerical results for a few benchmark problems in the context of polygonal finite elements that show the effectiveness of the method. [less ▲] Detailed reference viewed: 88 (0 UL) |
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