Strukturverwandtschaften zwischen trigonalen Verbindungen mit hexagonal-dichtester Anionen-Teilstruktur und besetzten Oktaederlücken. Berechnung der Anzahl möglicher Strukturtypen. II [1]

Structural Relations among Trigonal Compounds with Hexagona Closest-packing of Anions and Occupied Octahedral Voids. Calculation of the Numbers of Possible Structure Types, 2^nd Communication [1] The unit cell of the hexagonal closest-packing is enlarged trifold and trigonal symmetry is retained. When part of the octahedral voids are then occupied, several known crystal structure types result. The crystallographic group-subgroup relations are shown. For each of the space groups the number of possible independent structure types is calculated according to chemical composition. Known representatives include RhF₃, corundum, ilmenite, LiNbO₃, BiI₃, WCl₆, LiSbF₆, Na₃GdCl₆, and Li₂ZrF₆; distorted varieties are RuBr₃, PI₃ and N(CH₃)₃. No representative is known for one possible structure type for compounds MX₃ in the space group R32; it could be adopted by WCl₃ and contains pairs of face-sharing octahedra linked by common vertices.     

微孔压电弹性动力学的能量原理

根据古典阴阳互补和现代对偶互补的基本思想,通过作者早已提出一条简单而统一的新途径,系统地建立了微孔压电弹性动力学的能量原理,给出一个重要的以卷积表示的积分关系式,可以认为,在力学上它是广义虚功原理的表式,从该式出发,不仅能得到微孔压电弹性动力学的虚功原理和互等定理,而且通过作者所给出的一系列广义Legendre变换,能系统地导出成互补关系的11类变量、9类变量、6类变量和3类变量简化Gurtin型变分原理的泛函,同时,通过这条新途径,还能清楚地阐明这些原理之间的内在联系。     

RESPONSE OF MICROPOLAR THERMOELASTIC SOLID WITH VOIDS DUE TO VARIOUS SOURCES UNDER GREEN NAGHDI THEORY

Green-Naghdi (G-N) theory of thermoelasticity is employed to study the deformation of micropolar thermoelastic solid with voids considering the influence of varions sources acting on the plane surface....     

移动周期载荷作用下孔隙热弹性地基的动力学响应

根据孔隙热弹性线性理论,本文首先建立了在移动周期载荷作用下孔隙热弹性地基动力学响应分析的数学模型,其中提出了在周期性边界上必须满足的6类适当的条件,即界面位移相等、应力相等、孔隙百分比相等、温度相等以及在外法线方向孔隙发展相等和温度导数相等。在此基础上,分别采用微分求积法(DQM)和有限差分法(FDM)对控制方程进行空间和时间离散,并求解。作为算例,分别研究了在移动周期载荷和极限车载作用下孔隙热弹性地基的动力学响应,考察了车速对沉降、孔隙体积百分比和温度的影响。可以看到,本文提出的处理周期性问题DQM,具有精度高、收敛性好,计算效率高等特点。     

Proof of Straley's argument for bootstrap percolation

We prove thatP _c =1 for bootstrap percolation with large void instabilities (in particular, ifm=3 on the square lattice).     

A Study on the Generating Mechanism of Vertical Joints in Loess

Based on field investigation, theoretical analysis and model testing, the authors believe that the horizontal tensile stress caused by gravity at the top and bottom of big voids or holes is the primary rea-. son for the generation of vertical joints in loess. This paper explains the generation mechanism of vertical joints in loess from the viewpoint of mechanics for the first time.     

The influence of imperfections on the creep behavior of woven polymer composites at elevated temperatures

The dynamic behavior of compression molded polymer/woven graphite fiber composites at elevated temperatures is investigated analytically. This is performed with the objective of predicting the initiation of catastrophic failure that may occur after prolonged usage of the material at these temperatures. Special attention is paid to the behavior of the voids present in them where the failure may occur. The polymer matrix is modeled as a 4-parameter model (Maxwell-Voigt combination) (Govindarajan et al., in: Advances in Computer-Aided Engineering, ASME, 1994) while the composite structure is modeled using the fiber undulation model (Ishikawa and Chou, J. Mater. Sci. 17, pp. 3211–3220, 1982). The relation between the polymer properties and the ambient temperature is modeled after Arhenius' relation (Govindarajan et al., 1994; Ferry, Viscoelastic Properties of Polymers, Wiley, New York, 1961). The multiple phases in the matrix are taken into account through Eshelby's theory (Proc. Royal Soc. London A 241, pp. 376–396, 1957) and its extension for multiple occurrences of the same phase (Tanden and Weng, Polymer Composites 5, pp. 327–333, 1984; Weng, Internat. J. Eng. Sci. 22 (7), pp. 845–856, 1984) which assumes an ellipsoidal shape for inclusions. The resulting elastic equations are transformed into the time domain using Laplace transformation and the correspondence principle (Govindarajan et al., 1994; Wang and Weng, ASME J. Appl. Mech, 1992). All the voids are considered to be prolate ellipsoids with the 1-axis being the axis of symmetry. The distribution of voids is assumed to be of a Gaussian form with respect to the aspect ratio. The response of the composite under creep condition (constant load) has been simulated. Relations between the applied stress and the stresses in the matrix/void phase are also supplied, so that the influence of the voids may be characterized. The model is then applied to simulate the behavior of an epoxy/woven graphite composite to obtain the numerical results.