Elastic field perturbation by a misfitting ring inclusion

The plane elasticity problem of a circular ring inhomogeneity, with either a hollow or a rigid core, is confronted. A solution is obtained under a wide class of loading conditions, the main limitation being that internal stress sources (if any) are located in the matrix. In order to take into account interfacial residual stresses, misfit between matrix and inhomogeneity is allowed. Loading by misfit alone, by uniform remote stresses, and by an edge dislocation, are explicitly treated as special cases.     

Effect of temperature on dislocation emission from crack tip for BCC metal Mo

The effect of thermally activated energy on the dislocation emission from a crack tip in BCC metal Mo is simulated in this paper. Based on the correlative reference model on which the flexible displacement boundary scheme is introduced naturally, the simulation shows that as temperature increases the critical stress intensity factor for the first dislocation emission will decrease and the total number of emitted dislocations increase for the same external load. The dislocation velocity and extensive distance among partial dislocations are not sensitive to temperature. After a dislocation emission, two different deformation states are observed, the stable and unstable deformation states. In the stable deformation state, the nucleated dislocation will emit from the crack tip and piles up at a distance far away from the crack tip, after that the new dislocation can not be nucleated unless the external loading increases. In the unstable deformation state, a number of dislocations can be emitted from the crack tip continuously under the same external load. The project is supported by the National Natural Science Foundation of China.     

An improvement of the Peierls equation by taking into account the lattice effects

An improvement of the Peierls equation has been made by including the lattice effects. By using the non-trivially gluing mechanism for the simple cubic lattice, in which atoms interact with its first and second nearest neighbours through a central force, the dislocation equation has been derived rigorously for the isotropic case. In the slowly varying approximation, the Peierls equation with the improvement by including the lattice effects has been obtained explicitly. The new equation can be used to substitute for the old one in theoretical investigations of dislocations. The major change of the predicted dislocation structure is in the core region. The width of the dislocation given by using the new equation is about three times that given by the classical Peierls--Nabarro theory for the simple cubic lattice.     

A model of size effects in nano-indentation

The indentation hardness-depth relation established by Nix and Gao [1998. Indentation size effects in crystalline materials: a law for strain gradient plasticity. J. Mech. Phys. Solids 46, 411-425] agrees well with the micro-indentation but not nano-indentation hardness data. We establish an analytic model for nano-indentation hardness based on the maximum allowable density of geometrically necessary dislocations. The model gives a simple relation between indentation hardness and depth, which degenerates to Nix and Gao [1998. Indentation size effects in crystalline materials: a law for strain gradient plasticity. J. Mech. Phys. Solids 46, 411-425] for micro-indentation. The model agrees well with both micro- and nano-indentation hardness data of MgO and iridium.     

518例先天性髋关节脱位筛查结果分析

报道了518例先天性髋关节脱位筛查结果，并对造成该病的原因进行了讨论。     

内耗研究的历史评述

通过介绍几位在内耗领域的先驱研究者：C．Zener，葛庭燧，P．G．Bordoni，J．L．Snoek，评述了内耗研究的进展．也介绍了日本研究者的相关工作。     

Brittle-ductile behavior in 3D iron crystals

We present large scale molecular dynamic (MD) simulations in bcc iron containing a relatively long Griffith crack loaded in mode I at a temperature of K and 300 K. We use N-body potentials of Finnis-Sinclair type. The paper also includes a stress analysis performed in the framework of anisotropic fracture mechanics and on the atomic level as well. It enables us to understand why at 0 K brittle fracture in MD is detected, while at 300 K ductile behavior at the crack front in MD is monitored, starting from the free sample surface.     

Continuous description of a grain boundary in forsterite from atomic scale simulations: the role of disclinations

We present continuous modelling at inter-atomic scale of a high-angle symmetric tilt boundary in forsterite. The model is grounded in periodic arrays of dislocation and disclination dipoles built on information gathered from discrete atomistic configurations generated by molecular dynamics simulations. The displacement, distortion (strain and rotation), curvature, dislocation and disclination density fields are determined in the boundary area using finite difference and interpolation techniques between atomic sites. The distortion fields of the O, Si and Mg sub-lattices are detailed to compare their roles in the accommodation of lattice incompatibility along the boundary. It is shown that the strain and curvature fields associated with the dislocation and disclination fields in the ‘skeleton’ O and Si sub-lattices accommodate the tilt incompatibility, whereas the elastic strain and rotation fields of the Mg sub-lattice are essentially compatible and induce stresses balancing the incompatibility stresses in the overall equilibrium.     

The structure of a propagating MgAl2O4/MgO interface: linked atomic- and μm-scale mechanisms of interface motion

To understand how a new phase forms between two reactant layers, MgAl₂O₄ (spinel) has been grown between MgO (periclase) and Al₂O₃ (corundum) single crystals under defined temperature and load. Electron backscatter diffraction data show a topotaxial relationship between the MgO reactant and the MgAl₂O₄ reaction product. These MgAl₂O₄ grains are misoriented from perfect alignment with the MgO substrate by ~2–4°, with misorientation axes concentrated in the interface plane. Further study using atomic resolution scanning transmission electron microscopy shows that in 2D the MgAl₂O₄/MgO interface has a periodic configuration consisting of curved segments (convex towards MgO) joined by regularly spaced misfit dislocations occurring every ~4.5 nm (~23 atomic planes). This configuration is observed along the two equivalent [1 0 0] directions parallel to the MgAl₂O₄/MgO interface, indicating that the 3D geometry of the interface is a grid of convex protrusions of MgAl₂O₄ into MgO. At each minimum between the protrusions is a misfit dislocation. This geometry results from the coupling between long-range diffusion, which supplies Al³⁺ to and removes Mg²⁺ from the reaction interface, and interface reaction, in which climb of the misfit dislocations is the rate-limiting process. The extra oxygen atoms required for dislocation climb were likely derived from the reactant MgO, leaving behind oxygen vacancies that eventually form pores at the interface. The pores are dragged along by the propagating reaction interface, providing additional resistance to interface motion. The pinning effect of the pores leads to doming of the interface on the scale of individual grains.