横观各向同性体应力波传播问题的特征分析

本文根据广义特征理论,对横观各向同性体轴对称弹性波传播问题进行了理论分析。提出了一个简化特征分析的方法,这种方法将成为应用特征线法求解各类各向异性应力波问题的一个突破口。     

复合材料层板边缘效应的准相似元解法

用准相似单元法研究了复合材料层板直边和孔边的自由边缘效应，得到了一些具有工程意义的结果。准相似单元法是相似单元法的推广，利用这一方法可以求解三维的应力集中问题，避免了求单刚时的重复计算。由于采用了按相似层求解的技术，应用准相似单元法求解应力集中问题时对计算机容量的要求大为降低     

Raman imaging and stress quantification in self‐assembled graphene oxide fiber ‘Latin Letters’

To probe the intrinsic stress distribution in terms of spatial Raman shift (ω) and change in the phonon linewidth (Γ), here we analyze self‐assembled graphene oxide fibers (GOF) ‘Latin letters’ by confocal Raman spectroscopy. The self‐assembly of GOF ‘Latin letters’ has been explained through surface tension, π–π stacking, van der Waals interaction at the air–water interface and by systematic time‐dependent investigation using field emission scanning electron microscopy analysis. Intrinsic residual stress due to structural joints and bending is playing a distinct role affecting the E_2g mode (G band) at and away from the physical interface of GOF segments with broadening of phonon linewidth, indicating prominent phonon softening. Linescan across an interface of the GOF ‘letters’ reveals Raman shift to lower wavenumber in all cases but more so in ‘Z’ fiber exhibiting a broader region. Furthermore, intrinsic stress homogeneity is observed for ‘G’ fiber distributed throughout its curvature with negligible shift corresponding to E_2g mode vibration. This article demonstrates the significance of morphology in stress distribution across the self‐assembled and ‘smart‐integrable’ GOF ‘Latin letters’. Copyright © 2016 John Wiley & Sons, Ltd.     

考虑横向剪切变形的扁球壳在集中力作用下的分析

采用适于夹层壳的直线假设扁壳理论，应用三角级数法，导出了扁球壳齐次方程的解析解。进而分析了在顶点作用法向集中力和在偏心集中力作用下的解。计算了在偏心集中力作用下带孔球壳的位移和应力，并将结果与经典理论的结果进行了比较分析，结果表明，在集中力作用处和孔边处两种理论结果明显不同。     

Maxwell粘弹性球体的湿应力

谷物烘干时，谷粒内部的热－湿应力太大，可能使谷粒出现裂纹．基于这一实际问题，本文研究了当初始湿度和平衡湿度给定时，Ｍａｘｗｅｌ粘弹性圆球内的湿应力分布，及其随时间的变化情况．     

Diffusion of moisture in deformable porous media. Anisotropic fibrous materials

This paper presents a study on the deformation of anisotropic fibrous porous media subjected to moistening by water in the liquid phase. The deformation of the medium is studied by applying the concept of effective stress. Given the structure of the medium, the displacement of the solid matrix is not taken into account with respect to the displacement of the liquid phase. The transport equations are derived from the model proposed by Narasimhan. The transport coefficients and the relation between the variation in apparent density and effective stress are obtained by test measurements. A numerical model has been established and applied for studying drip moistening of mineral wool samples capable or incapable of deformation.Nomenclature D mass diffusion coefficient [L²t^–1] - e void fraction - g gravity acceleration [Lt^–2] - J mass transfer density [ML^–2t^–1] - K hydraulic conductivity [Lt^–1] - K _s hydraulic conductivity of the solid phase [Lt^–1] - K ^* hydraulic conductivity of the deformable porous medium [Lt^–1] - P pressure of moistening liquid [ML^–1 t^–2] - S degree of saturation - t time [t] - V speed [Lt^–1] - X horizontal coordinate [L] - Z vertical coordinate measured from the bottom of porous medium [L] - z z-coordinate [L] Greek Letters porosity - ₁ total hydric potential [L] - _g gas density [ML^–3] - ₁ liquid density [ML^–3] - ₀ apparent density [ML^–3] - _s density of the solid phase [ML^–3] - density of the moist porous medium [ML^–3] - external load [ML^–1t^–2] - effective stress [ML^–1t^–2] - bishop's parameter - matrix potential or capillary suction [L] Indices g gas - 1 moistening liquid - p direction perpendicular to fiber planes - s solid matrix - t direction parallel to fiber planes - v pore Exponent * movement of solid particles taken into account     

A new phenomenon of acoustic streaming

This paper describes a new phenomenon of acoustic streaming which takes place when a Helmholtz resonator is excited by an inside sound source with resonant frequency, and takes the form of a strong turbulent jet. The flow visualizations, hot wire and LDV measurements are combined to investigate the process of acoustic streaming. It is found that this kind of acoustic streaming results from the contribution of Reynolds stress.     

A centrally cracked thin circular disk, Part I: 3D Elastic–plastic finite element analysis

A full field solution, based on small deformation, three-dimensional elastic–plastic finite element analysis of the centrally cracked thin disk under mode I loading has been performed. The solution for the stresses under small-scale yielding and lo!cally fully plastic state has been compared with the HRR plane stress solution. At the outside of the 3D zone, within a distance of rσ_o/J=18, HRR dominance is maintained in the presence of a significant amount of compressive stress along the crack flanks. Ahead of this region, the HRR field overestimate the stresses. These results demonstrate a completely reversed state of stress in the near crack front compared to that in the plane strain case. The combined effect of geometry and finite thickness of the specimen on elastic–plastic crack tip stress field has been explored. To the best of our knowledge, such an attempt in the published literature has not been made yet. For the qualitative assessment of the results some of the field parameters have been compared to the available experimental results of K, gives a fair estimate of the crack opening stress near the crack front at a distance of order 10⁻² in. On the basis of this analysis, the Linear Elastic Fracture Mechanics approach has been adopted in analyzing the fatigue crack extension experiments performed in the disk (Part II).     

The effect of velocity on rigid wheel performance

A simulation model to predict the effect of velocity on rigid-wheel performance for off-road terrain was examined. The soil–wheel simulation model is based on determining the forces acting on a wheel in steady state conditions. The stress distribution at the interface was analyzed from the instantaneous equilibrium between wheel and soil elements. The soil was presented by its reaction to penetration and shear. The simulation model describes the effect of wheel velocity on the soil–wheel interaction performances such as: wheel sinkage, wheel slip, net tractive ratio, gross traction ratio, tractive efficiency and motion resistance ratio. Simulation results from several soil-wheel configurations corroborate that the effect of velocity should be considered. It was found that wheel performance such as net tractive ratio and tractive efficiency, increases with increasing velocity. Both, relative wheel sinkage and relative free rolling wheel force ratio, decrease as velocity increases. The suggested model improves the performance prediction of off-road operating vehicles and can be used for applications such as controlling and improving off-road vehicle performance.     

一种新的弹塑性杂交应力元法

本文基于一个改进的弹塑性的Hellinger/Reis■ner 混合变分原理构造了一种用于解弹塑性问题的四节点等参杂交应力元.新的模型中,在单元内增加了等效应力增量、塑性等效应变增量及不协调位移变量,从而使单元内的屈服准则及流动法则平均得到满足,不协调位移改进了单元应力精度.计算表明,新的模型可以提高弹塑性杂交法的精度和计算效率.