Effects of Crystal Orientations on the Low-Cycle Fatigue of a Single-Crystal Nickel-Based Superalloy at 980 °C

The influence of crystal orientations on the low-cycle fatigue(LCF) behavior of a 3Re-bearing Ni-based single-crystal superalloy at 980 °C has been investigated. It is found that the orientation dependence of the fatigue life not only depends on the elastic modulus, but also the number of active slip planes and the plasticity of materials determine the LCF life,especially for the [011] and [111] specimens. The [011] and [111] specimens with better plasticity withstand relatively concentrated inelastic deformation caused by fewer active slip planes, compared to the [001] specimens resisting widespread deformation caused by a higher number of active slip planes. Additionally, fatigue fracture is also influenced by cyclic plastic deformation mechanisms of the alloy with crystal orientations, and the [001] specimens are plastically deformed by wave slip mechanism and fracture along the non-crystallographic plane, while the [011] and [111] specimens are plastically deformed by planar slip mechanism and fracture along the crystallographic planes. Moreover, casting pores,eutectics, inclusions and surface oxide layers not only initiate the crack, but also reduce the stress concentration around crack tips. Our results throw light upon the effect of inelastic strain on the LCF life and analyze the cyclic plastic deformation for the alloy with different orientations.     

各向异性基底鳍线的理论分析

本文首次从双折射晶体的基本性质出发对各向异性基底鳍线波导进行了严格的理论分析。在谱域坐标系中确立了寻常波和非常波的波矢及电场偏振特性与晶体基片主轴取向的一般关系，标量波动方程和场解，以Ｚ切和Ｙ切单轴晶体为例给出了场结构和Ｇ矩阵的解析表达式。     

Improvement of the figure-of-merit by formation of crystallographic texture in Bi2Te3-based thermoelectric compounds

Coarse powders of 200∼300 μm size and fine powders below 45 μm size were blended with various ratios, and then synthesized by spark plasma sintering method. The use of coarse powders was beneficial to improve the crystallographic orientation and addition of fine powders reduced the voids existing between coarse powders. When 20 wt% of fine powders were blended with coarse powders, the sintered compound exhibited the maximum figure-of-merit.     

Variability of pressure drops in grain generated by kernel shape and bedding method

Experiments were performed to evaluate the influence of seed shape and the packing orientation of seeds on the pressure drop. Relationships between the pressure drop and airflow velocity of five seeds were determined as a function of filling method and its influence on kernel orientation. The sample container was a cube with a length of 0.35 m on each side that held approximately 35 kg of clean wheat. Eleven airflow rates were supplied in a range from 0.03 to 0.35 m s⁻¹. Seeds that were nearly spherical (rapeseed and pea) as well as oblong seeds (wheat, rye and oats) were used for the tests. Three filling methods of the cube were used, including one that produced asymmetric particle orientation (bedding) within the grain sample. Pressure drop was measured in all three directions: the vertical (Z) and both horizontal directions (X and Y). Results obtained from the experiments showed that seed shape and the filling method strongly influenced pressure drop. At an air velocity of 0.3 m s⁻¹, when the cube was filled along the vertical axis the uncompacted samples had a pressure drop in the vertical direction that was 1.1 (peas) to 2.1 (oats) times higher than the pressure drops along the X and Y axes. The pressure drops along the X and Y axes were approximately equal. Compaction of the sample filled vertically resulted in the pressure drop in the vertical direction increasing between 1.7 (wheat, rye and peas) and 2.4 (oats) times the pressure drop in the uncompacted sample. In asymmetrically filled samples the pressure drops along the horizontal directions increased by a factor of 2.2 relative to the centrally filled samples.     

Construction of anisotropic polyconvex energies and applications to thin shells

In computer simulations where constitutive equations are considered anisotropic polyconvex energies can preferably be used because the existence of minimizers is then automatically guaranteed. In this work we investigate the capability to simulate anisotropy effects of anisotropic thin shells using polyconvex anisotropic energies. The construction of the considered polyconvex transversely isotropic energy is based on specific structural tensors. The iterative enforcement of the zero normal stress condition at the integration points allows the consideration of arbitrary three-dimensional constitutive equations. As a representative example we compare results for isotropic and anisotropic plates.     

Development of viscoelastic/rate-sensitive-plastic constitutive law for fiber-reinforced composites and its applications. Part I: Theory and material characterization

The viscoelastic/rate-sensitive plastic constitutive law to describe the nonlinear, anisotropic/asymmetric and time/rate-dependent mechanical behavior of fiber-reinforced (sheet) composites was developed under the plane stress condition. In addition to the theoretical aspect of the developed constitutive law, experiments to obtain the material parameters were also carried out for the woven fabric composite based on uni-axial tension and compression tests as well as stress relaxation tests, while the numerical formulation and verifications with experiments are discussed in Part II.     

Micro-Macro Quantification of the Internal Structure of Granular Materials

We have attempted a multiscale quantification of the internal structure of granular materials. The internal structure of granular materials, i.e., the geometrical information on granular particles and their spatial arrangement, was described mathematically on the particle scale using Voronoi–Delaunay tessellations. These tessellations were further modified into two cell systems: a solid cell system and a void cell system, with the internal supporting structure properly reflected. By doing so, the two cell systems were geometrically and physically significant. Taking solid/void cells as the microscopic basic elements, the behavior of granular materials was expressed as the volumetric average of the microcell behavior. Macroscopically, the internal structure could be characterized by the statistical measures from the geometry of the microcells. Our approach was used to investigate the anisotropic behavior of granular materials. A study on the void cells explains how the spatial arrangement affects the strength and dilatancy of granular materials. A new anisotropic fabric tensor was defined based on the void cell anisotropy. The correlation between the anisotropic fabric tensor and the macro behavior of granular materials was verified with numerical simulations. The results showed that the new material anisotropic tensor is a more effective definition than the existing ones based on particle orientations and contact normals.     

Mechanical properties and chemical bonding characteristics of WC and W2C compounds

The mechanical properties and chemical bonding features of W–C binary compounds (h-WC, o-W₂C, h-W₂C and t-W₂C) were studied by density functional theory (DFT). It is shown that they are thermodynamically stable identified by the cohesive energy and formation enthalpy of W–C binary compounds. The elastic constants were calculated using the stress–strain method. The Voigt–Reuss–Hill approximation was used to evaluate the moduli. The surface constructions of bulk and Young's moduli were applied to illustrate the mechanical anisotropy. The population analysis of W–C binary compounds was used to discuss the chemical bonding, which indicate the combinations of covalent and metallic bonds in these compounds. Moreover, the anisotropic properties of sound velocities for W–C binary compounds were explored.     

Transmission Mueller matrix ellipsometry of chirality switching phenomena

Mechanisms of molecular chirality induction are fundamental to many questions in chemistry. Interest in these mechanisms is shifting toward media of increasing complexity that simultaneously exhibit linear birefringence and dichroism and where the common assumption that optical activity is the only optical effect that affects light polarization is no longer valid. Light propagation through several of these anisotropic media can be appropriately studied with transmission Mueller matrix ellipsometry. The applications presented herein include the measurement of optical activity in stirred solutions of soft-matter nanophases and the determination of chiral domains in solid-state samples.