Restructuring of emergent grain boundaries at free surfaces – an interplay between core stabilization and elastic stress generation

Scanning tunneling microscopy and numerical calculations are used to study the structure and relaxation of grain boundaries at the surface of planar nanocrystalline copper (111) films and bicrystals. We show that the strong energetic preference for boundary cores to lie along close-packed planes introduces a restructuring that rotates adjoining grains and generates elastic stresses in the triple junction region. The interplay of this stress field and the core stabilization determines the length scale of the restructuring and controls the shape and magnitude of the displacement field around the triple junction. Depending on the in-plane angle, restructured boundaries can extend to depths of ~ 15 nm with the associated elastic stress fields extending to even greater depths. These results point to a new mechanism of boundary relaxation at surfaces that is expected to play an important role in grain coalescence and stress evolution in growing films.

Non-linear creep of polypropylene utilizing multiple integral

<p>Multiple integral representation (MIR) has been used to represent studying the effect of temperature on the amount of nonlinear creep on the semi- crystalline polypropylene (PP) under the influence of axial elastic stress. To complete this research, the Kernel functions were selected, for the purpose of performing an analogy, and for arranging the conditions for the occurrence of the first, second and third expansion in a temperature range between 20 °C-60 °C, i.e., between the glass transition and softening temperatures, within the framework of the energy law. It was observed that the independent strain time increased non-linearly with increasing stress, and non-linearly decreased with increase in temperature, although the time parameter increased non-linearly with stress and temperature directly. In general, a very satisfactory agreement between theoretical and practical results on the MIR material was observed.</p>

Radiation defects in NaCl matrix with reduced lattice symmetry caused by light cation doping and elastic uniaxial deformation

The processes of radiation defect creation and radiative relaxation of electronic excitations under applied local or/and uniaxial elastic deformation have been studied in NaCl crystals by means of optical absorption, luminescence and thermoactivation spectroscopy methods. In NaCl:Li at 80 K, X-ray-induced absorption bands peaked around 3.35 and 4.6 eV have been detected and ascribed to interstitial halide atoms located nearby Li impurity cations, HA(Li) centres. Subsequent thermal annealing of HA(Li) centres leads to the formation of polyhalide centres responsible for the absorption band at 5.35 eV. In an X-irradiated and stressed NaCl:Li crystal (degree of uniaxial elastic deformation of ε = 0.9%), the peak of thermally stimulated luminescence at ~115 K is composed of the ~2.7-eV emission appearing, in our opinion, due to the recombination of the electron, thermally released from an F′ centre, with a hole-type HA(Li) centre. The applied uniaxial elastic stress facilitates the self-trapping of anion excitons in regular regions of a NaCl lattice and impedes the energy transfer by mobile excitons to impurities/defects and, in turn, attenuates the Br-related luminescence peaked at 3.95 eV with respect to the π-emission of self-trapped excitons (~3.35 eV). The 3.95 eV emission has been detected in a natural NaCl crystal containing homologous Br impurity ions.

A semi-analytical elastic stress solution for circular rock stratum based on the theory of curved beam

The circular rock stratum are inevitably encountered in underground mining engineering, which causes waste of resources and dynamic instability. Based on the elastic theory of curved beam and finite-difference computation, a displacement function is presented in polar coordinates for solving two partial differential equations with the boundary conditions in mixed type in elastic, isotropic and homogeneous rock. A semi-analytical elastic stress solution for circular rock stratum is obtained according to the governing equation and stress components in terms of displacement function. The variations of stress distribution with different influencing factors are analyzed, which may lead to a better understanding of the stability of circular rock stratum after coal extractions. Finally, this semi-analytical elastic stress solution is applied to the fold structure in No.2502 mining area and points out the dangerous sites during coal extractions, which provides the basis of construction and safety in coal mine engineering.

Internal structures and mechanical properties of magnetic gels and suspensions

We present results of theoretical and computer study of linear chain-like and complicated labyrinth structures in magnetic gels and suspensions as well as effect of these internal structures on macroscopic elastic properties of the composites. Our results show that at a certain threshold deformation, the structures experience a rupture which provokes a fall down of the macroscopic elastic stress, induced by the deformation. This effect is detected for both shear and tensile deformations. The results of calculations are compared with experimental data’s.