Triaxial Small-Strain Viscoelastic-Viscoplastic Modeling of Asphalt Aggregate Mixes

A triaxial cross-anisotropic viscoelastic-viscoplastic constitutive model for asphalt aggregate mixtures is developed for the small-strain domain. The model follows the concept of strain decomposition by separately analyzing the viscoelastic and viscoplastic strain components. In order to calibrate the model, advanced triaxial testing was employed which included both hydrostatic and uniaxial creep and recovery cycles. The test-data is presented and analyzed along with the derivation of all model parameters. It is shown that the proposed model correlates extremely well with the entire test-data in both axial and radial directions.     

Modeling Density and Anisotropy of Energetic Electrons Along Magnetic Field Lines

The electromagnetic wave growth or damping depends basically on the number density and anisotropy of energetic particles as the resonant interaction takes place between the particles and waves in the magnetosphere. The variance of both the number density and anisotropy along the magnetic field line is evaluated systematically by modeling four typically prescribed distribution functions. It is shown that in the case of ＂the positive anisotropy＂ （namely, the perpendicular temperature T⊥ exceeds the parallel temperature T｜｜）, the number density of energetic electrons always decreases with the magnetic latitude for a regular increasing magnetic field and the maximum wave growth is therefore generally confined to the equator where the resonant energy is minimum, and the number density is the largest. However, the ＂loss-cone＂ anisotropy of the electrons with a ＂pancake＂ distribution or kappa distribution keeps invariant or nearly invariant, whereas the ＂temperature＂ anisotropy with a pure bi-Maxwellian distribution or Ashour-Abdalla and Kennel＇s distributions decreases with the magnetic latitude. The results may provide a useful approach to evaluating the number density and anisotropy of the energetic electrons at latitudes where the observation information is not available.     

Coupled damage tensors and weakest link theory for the description of crack induced anisotropy in concrete

Crack induced anisotropy in concrete is modeled within the general framework of damage mechanics. The damage state, formulated by using the effective stresses, is described by two second order tensors for direct and for induced cracks, respectively. These variables are deduced from different causes of deterioration by the generalized weakest link theory. The major contributions of this paper are the development of a failure criterion in multiaxial compression loading, and the definition of a projection method for assessing the effects of an initial oriented damage in any loading direction. The model is applied to the numerical analysis of concrete structures and the results are compared to available experimental data.     

用横波波速测定岩石的各向异性

测量了横波在各向异性岩石样品中以不同偏振角度传播时的波速。研究了井下岩石样品在干燥、含水饱和与煤油饱和状态下的各向异性情况。计算出这3种情况下岩石样品的时差各向异性常数和横波平均速率。在干燥、含水饱和与含油饱和条件下，含水饱和的各向异性系数有最大值；干燥的各向异性系数有最小值。在含油饱和情况下的横波平均声速要大于含水饱和条件下的横波平均声速。含油饱和与含水饱和条件下的横波速度有明显差别，但各向异性的趋势却比较一致。     

Simulation of the Fading Memory of Form of the Trajectory in the Theory of Simple Materials with Elastoplastic Behavior. Part 1. Finite Strains

We propose a mathematical theory of rigorous construction and specialization of determining relations for hardening elastoplastic materials simple in Noll's sense with fading memory of the form of trajectory in which plastic strains occur immediately after the application of loading and monotonically increase in the process of deformation. Strains and the type of symmetry of the material are arbitrary. For the processes of deformation close to proportional and slightly different from the stress- and strain-free configuration, we deduce physical equations for materials without memory of form of the trajectory with weakly fading memory, and fading memory of the nth order. On the basis of these equations, we deduce determining relations for isotropic materials.     

Thermoelectric properties for P-type (Bi2Te3)0.2(Sb2Te3)0.8 alloys fabricated by shear extrusion

P-type (Bi₂Te₃)_0.2(Sb₂Te₃)_0.8 compounds were synthesized via bulk mechanical alloying (BMA), and subsequently prepared by a shear extrusion process in order to create the developed texture. The shear extrusion process improved the preferred orientation factor of the anisotropic crystallographic structure. It was found by an electron backscattered diffraction pattern (EBSP) analysis that approximately 90% of the crystallographic orientations for shear-extruded sample are aligned in the range deviated from 60° to 90° from the c-axis. The electric resistivity is well controlled at 1.008×10⁻⁵Ωm, which is nearly equal to that of the unidirectionally grown sample. The maximum figure of merit for the (Bi₂Te₃)_0.2(Sb₂Te₃)_0.8 alloy was found to be z=3.03×10⁻³K⁻¹. The bending strength of the material produced is also improved to 120 MPa, six times larger than that of the unidirectionally grown sample.     

Phonon Dispersion Measurements of YBa2Cu3O6.15 and YBa2Cu3O6.95 by Time-of-Flight Neutron Spectroscopy

We measured the phonon dispersions of YBa₂Cu₃O_6.15 and YBa₂Cu₃O_6.95 by time-of-flight inelastic neutron scattering. The in-plane bond-stretching modes in the metallic phase showed a distinct a-b plane anisotropy beyond what is expected for structural origin. Such anisotropy in the longitudinal optical modes, which is absent in the TO, suggests strong in-plane anisotropy in the underlying electronic structure. Apical oxygen bond-stretching modes showed a large frequency change between the insulating and the metallic phases. This large softening also is beyond structural origin, and suggests the effect of local electronic environment.     

差分法模拟地震波勘探

本文利用Ｔａｙｌｏｒ级数展开和弹性力学波动方程的变换，得到既适用于各向同性介质，也适应于各向异性介质非规则网格的差分方法。计算结果表明，该方法的精度与常规的规则网格差分方法相当。     

各向异性对无切变边界层与轴对称应变湍流特性的影响

本文运用湍流快速畸变理论对各向异性条件对无切变边界层及轴对称应变湍流特性的影响进行了探讨，对无切变边界层，所进行扮析与实验资料表明，此时各向异性的影响在于增加纵向紊动强度及减小横向紊动强度，但其对垂向紊动影响甚小，对轴对称应变湍流，本文也对紊动强度与雷诺应力随向各异性条件的变化进行了分析。     

Interfacial Effects on the Dynamic Mechanical Behavior of Weft-Knitted Glass Fiber Fabric-Reinforced Polypropylene Composites Produced of Commingled Yarns. Tensile and Flexural Response

Weft knitted glass fiber (GF) fabric-reinforced polypropylene (PP) composite sheets were produced by hot pressing of knit layers composed of a commingled yarn with a GF content of 70 wt.%(≈45 vol.%). The effects of fiber/matrix adhesion and reinforcing knit-induced stiffness anisotropy were characterized by dynamic-mechanical thermoanalysis (DMTA). DMTA spectra were registered under tensile and flexural loading in both course (C) and wale (W) direction of the knit. The knit structure-related stiffness anisotropy (relation of the Young's moduli measured inW- andC-directions, respectively), which proved to depend also on the loading mode of the composites, were well reflected in the DMTA spectra. The detrimental effect of poor adhesion between GF and PP could be clearly resolved when specimens cut in theC-direction were investigated. This seems to be in analogy with the transverse mechanical response of undirectional (UD) fiber-reinforced composites with interfacial variations. It was suggested that the heating-induced lofting of the composites is relied on the bond quality between GF and PP.