Diffraction of SH-waves by topographic features in a layered transversely isotropic half-space

Abstract： The scattering of plane SH-waves by topographic features in a layered transversely isotropic （TI） half-space is investigated by using an indirect boundary element method （IBEM）. Firstly, the anti-plane dynamic stiffness matrix of the layered TI half-space is established and the free fields are solved by using the direct stiffness method. Then, Green＇s functions are derived for uniformly distributed loads acting on an inclined line in a layered TI half-space and the scattered fields are constructed with the deduced Green＇s functions. Finally, the free fields are added to the scattered ones to obtain the global dynamic responses. The method is verified by comparing results with the published isotropic ones. Both the steady-state and transient dynamic responses are evaluated and discussed. Numerical results in the frequency domain show that surface motions for the TI media can be significantly different from those for the isotropic case, which are strongly dependent on the anisotropy property, incident angle and incident frequency. Results in the time domain show that the material anisotropy has important effects on the maximum duration and maximum amplitudes of the time histories.

Analysis of the Diffractive Deep Inelastic Scattering Data with Running Coupling and Gluon Number Fluctuations

We study the effects of running coupling and gluon number fluctuations in the latest diffractive deep inelastic scattering data. It is found that the description of the data is improved once the running coupling and gluon number fluctuations are included with x2/d.o.f. = 0.867, x2/d.o.f. = 0.923 and x2/d.o.f. = 0.878 for three different groups of experimental data. The values of diffusive coefficient subtracted from the fit are smaller than the ones obtained by considering only the gluon number fluctuations in our previous studies. The smaller values of the diffusive coefficient are in agreement with the theoretical predictions, where the gluon number fluctuations are suppressed by the running coupling which leads to smaller values of the diffusive coefficient.

Scattering of SH waves by a scalene triangular hill with a shallow cavity in half-space

In this study,a theoretical approach is used to investigate the scattering problem of circular holes under a scalene triangle on the surface.The wave displacement function is obtained by solving the Helmholtz equation that meets the zero-stress boundary conditions by adopting the method of separation of variables.Based on the complex function,multi-polar coordinate method,and region-matching technique,algebraic equations are established at auxiliary boundaries and free boundaries conditions in a complex domain.The auxiliary circle is used to solve the singularity of the reflex angle at the triangle corner.Then,according to sample statistics,the least squares method is used instead of the Fourier expansion method to solve the undetermined coefficient of the algebraic equations by discrete boundary.Numerical results show that the continuity of the auxiliary boundaries and the accuracy of the zero-stress boundaries are adequate,and the displacement of the free surface and the stress of the circular hole are related to the shape of the triangle,the position of the circular hole,the direction of the incident wave,and the frequency content of the excitation.Finally,time-domain responses are calculated by FFT based on the frequency domain theory,and the results reveal the wave propagation mechanism in a complicated structure.

Hybridizing micro-Ti with nano-B_(4)C particulates to improve the microstructural and mechanical characteristics of Mg-Ti composite

In this study,the effects of hybridizing micron-sized titanium particles with nano-sized boron carbide particles on the microstructural and mechanical properties of Mg-Ti composite were investigated.Microstructural characterization revealed grain refinement attributed to the presence of uniformly distributed micro-Ti particles embedded with nano-B_(4)C particulates.Electron back scattered diffraction(EBSD)analyses of the Mg-(Ti+B_(4)C)BM hybrid composite showed relatively more localized recrystallized grains and lesser tensile twin fraction,when compared to Mg-Ti.The evaluation of mechanical properties indicated that the best combination of strength and ductility was observed in the Mg-(Ti+B_(4)C)BM hybrid composite.The superior properties of the Mg-(Ti+B_(4)C)BM hybrid composite when compared to Mg-Ti can be attributed to the presence of nano-reinforcement,the uniform distribution of the hybridized particles and the better interfacial bonding between the matrix and the reinforcement particles achieved by nano-B_(4)C addition.

A note on near-field site amplification effects of ground motion from a radially inhomogeneous valley

To improve the understanding of the near-field soil and topographic amplification effects, an analytical solution by the authors for the scattering of plane SH waves by a radially inhomogeneous semi-cylindrical valley is extended to the case of a line source of cylindrical SH waves. Upon confirmation of its accuracy with past exact solutions for a homogeneous and an inhomogeneous semi-cylindrical valley under far-field plane SH waves, the extended solution is used to calculate the ground motion amplification factors for both the homogeneous and inhomogeneous valleys subjected to near-field waves. A comprehensive parametric study is conducted with respect to the location of the wave source, the dimensionless frequency of the incident waves, and the inhomogeneity degree of the covering soil layer. It is found that more amplifications and reductions of ground motions will occur within a certain range in and around the valley as the sources are located further. Consistent with the far-field case, it is confirmed that an increase of the degree of inhomogeneity of the covering soil layer generally amplifies the ground motions significantly.

Analysis on Microstructure and Misorientation of Ultrathin Hot Strip of Low Carbon Steel Produced by Compact Strip Production

The microstructure and misorientation of ultrathin hot strip were analyzed by CSP technology using electron back scattered diffraction (EBSD) method and Autoforge finite element program. The experimental results showed that the finishing hot rolling microstructures were the mixture of recrystallized and deformed austenite. After phase transformation, ferrite grains embody substructures and dislocations, leading to the high strength and relatively low elongation rate of the ultrathin hot strip. The FEM simulation of strain mode and distribution in deformation area has been fulfilled. The simulation results are in good agreement with the theoretical analysis and experimental results.

Microstructure and texture characteristics of ZK60 Mg alloy processed by cyclic extrusion and compression

The microstructure and crystallographic texture characteristics of an extruded ZK60 Mg alloy subjected to cyclic extrusion and compression(CEC) up to 8 passes at 503 K were investigated.The local crystallographic texture,grain size and distribution,and grain boundary character distributions were analyzed using high-resolution electron backscatter diffraction(EBSD).The results indicate that the microstructure is refined significantly by the CEC processing and the distributions of grain size tend to be more uniform with increasing CEC pass number.The fraction of low angle grain boundaries(LAGBs) decreases after CEC deformation,and a high fraction of high angle grain boundaries(HAGBs) is revealed after 8 passes of CEC.Moreover,the initial fiber texture becomes random during CEC processing and develops a new texture.

Acoustical diffraction tomographic imaging under non-weak scattering

Under the assumption of weak scattering , the acoustical diffraction tomographic imaging of an object can be reconstructed by using the Born (or Rytov) approximation method . When the weak scattering assumption within the medium is not satisfied the multiple ultrasound scattering must be taken into account . In this case , the reconstruction results under the first-order Born approximation will be seriously distorted . In this paper we introduce an ' intermediate object function' into the wave equation and take iterative modification in space domain and spatial frequancy domain based on Born approximation . In this way , the distorted image will be improved step by step . In order to examine the method as mentioned above , we have just tried to make computerized simulations . The initial result shows that the quality of the image reconstructed from the object under non-weak scattering may be improved significantly .

Recrystallization behavior of high purity aluminum at 300℃

The recrystallization behavior of 98.5% cold rolled high purity aluminum foils annealed at 300 ℃ was investigated,and the evolution of the microstructures was followed by electron back scattered diffraction(EBSD).The results show that the recrystallization process of the high purity aluminum foils at 300 ℃ is a mixture of discontinuous-and continuous-recrystallization.The orientations of the recrystallization nuclei include not only the cube orientation,but also other orientations such as some near deformation texture components which are the results of strong recovery process.However,such continuously recrystallized grains are usually associated with relatively high free energy,so they would be consumed by the discontinuously-recrystallized grains(cube-oriented grains)in subsequent annealing.On the other hand,the pattern quality index of recrystallized grains shows dependence on the crystal orientation which might introduce some errors into evaluating volume fraction of recrystallization by integrating pattern quality index of EBSD.

Achieving ultra-high strength in Mg-Gd-Ag-Zr wrought alloy via bimodal-grained structure and enhanced precipitation

Mg-13.1 Gd-1.6 Ag-0.4 Zr(wt%)alloy was either iso-thermally extruded at 350℃ or differentialthermally extruded with respectively pre-heated billet at 500℃ and die at 350℃.The iso-thermal extrusion leads to a near fully recrystallized structure and a[0001]//ED(extrusion direction)texture.In contrast,the differential-thermally extruded alloy develops a bimodal-grained structure composed of fine equiaxed recrystallized grains and coarse elongated unrecrystallized grains with a0110//ED texture.The differential-thermally extruded alloy has a higher number density of precipitates after postextrusion ageing than that of the iso-thermally extruded counterpart.Moreover,precipitation in the differential-thermally extruded alloy is further enhanced with cold rolling before ageing.Finally,the alloy obtains room temperature tensile yield strength of 421 MPa and ultimate tensile strength of 515 MPa via differential-thermal extrusion,cold rolling and ageing,mainly ascribed to the coupled strengthening from the bimodal-grained structure and enhanced precipitation.Strength of the alloy is noticeably higher than those of Mg-Gd(-Y)-Ag extruded alloys with similar compositions reported previously and is comparable to those of other high-strength Mg wrought alloys.The findings suggest that differentialthermal extrusion plus strain ageing is a suitable approach for achieving high strength in age-hardenable Mg alloys.

<110> Fiber Texture Evolution of Ferrite Wires during Drawn-torsion and Drawn-annealing-torsion Process

In this paper, the texture and microstructure evolution of drawn-torsion and drawn-annealing-torsion ferrite wires are studied by electron back scattering diffraction （EBSD） in order to investigate the special torsion texture evolution. Compared to the simulation results, the stable texture components {110}〈 110 〉 and {110}〈112〉 in both drawn-torsion and drawn-annealing-torsion wires display different evolution processes. The texture of the drawn-annealing-torsion wire fits to the Taylor model. A special texture evolution is found in drawn-torsion wires, related to the grain shape, and the heterogeneous deformation. A new plastic deformation viewpoint is suggested based on the special microstructure of drawn ferrite wire.