Stress Distributions around Holes in Composite Laminates Subjected to Biaxial Loading

An approximate solution has been derived for the in-plane stresses near a circular hole, in an orthotropic composite laminate under biaxial loading. The derived stresses were found to be in good agreement with the exact analytical solution, for a series of laminates investigated. However, the degree of accuracy of the approximate stress distribution is strongly influenced by the laminate lay-up and the biaxiality ratio. The resultant stresses could be employed in stress based fracture models to investigate the notch sensitivity and fracture mechanisms of composite plates with an open-hole subjected to biaxial loading.     

振动挤出过程中毛细管内聚合物熔体的剪切应力分析

不依赖现有的任何本构关系，并考虑惯性项的影响，建立了平行叠加振动条件下毛细管内聚合物熔体剪切应力的计算公式；实验测量一定振动频率和振幅下毛细管瞬时入口压力、瞬时体积流量、以及体积流量与入口压力波形的相位差，通过上述公式即可求得振动力场下毛细管内聚合物熔体的剪切应力分布。     

冲击载荷作用下动态应力强度因子的迭加积分法

介绍利用线性时不变系统求响应的迭加积分法(杜阿美尔积分)求解带裂纹构件的线弹性动态应力强度因子。即先求出结构的单位冲激响应,再与载荷做卷积求得总的响应;或者先计算出单位阶跃响应,再与载荷的微分做卷积来求得总的响应。理论和计算都证明了这两种迭加积分法的精度。在动态起裂韧度测试实验中,特别是用实验-数值法要处理同一组试样的大量实验数据,应用迭加积分法可以有效的避免数值求解的重复计算,减少计算量。     

Application of the Method of Singular Integral Equations to the Determination of the Contours of Equistrong Holes in Plates

We propose a procedure for the determination of the contours of equistrong holes in elastic plates based on the method of singular integral equations. The problem is reduced to the solution of inverse two-dimensional problems of the theory of elasticity with unknown boundaries. The singular integral equations of the direct problems are solved numerically by the method of mechanical quadratures. For plates with one, two, or a system of periodic holes loaded by biaxial tension at infinity and internal pressure on the contours of holes, we determine the parameters of the contours of equistrong holes. Some numerical results are compared with the available data obtained by using different methods. Good accuracy of numerical results is attained even for small numbers of the parameters of shape of the holes and nodal points on their contours, which confirms the efficiency of the proposed procedure.     

A General Equation for Stress Concentration in Countersunk Holes

A detailed and accurate three-dimensional finite element stress analysis was conducted on countersunk rivet holes in a plate subjected to tension loading. The analysis included a wide range of countersunk depths, plate thicknesses, countersunk angles and plate widths. The study confirmed some of the previous results, addressed their differences, provided many new results, and investigated countersunk angle and width effects. Using the detailed FE results and the limiting conditions, a general equation for stress concentration was developed and verified.     

An Equation for Stress Concentration Factor in Countersunk Holes

A detailed three-dimensional finite element stress analysis was conducted on straight-shank and countersunk rivet holes in a plate subjected to tension loading. The study included a wide range of plate width to radius, thickness to radius, countersunk depth to thickness ratios and countersunk angles(θ_c). The stress concentration is maximum at or near the countersunk edge. The stress concentration depends on countersunk depth, plate thickness and width and it is nearly independent of the countersunk angle for 80° ≤ θ_c ≤ 120°. Using the finite element results and limiting conditions, an equation for stress concentration factor is developed and verified.     

碳素钢在不同应力作用下的漏磁场分布特征

选取45#钢平板缺口试样进行拉伸实验,在线测量各组试样在不同拉伸载荷时的试样表面漏磁场分布;同时利用ANSYS有限元分析软件对各组试样在不同拉伸载荷下的应力分布进行有限元分析,并提取应力分布结果.分析了试样表面漏磁场分布与应力分布之间的关系以及应力对磁记忆信号的影响;在磁记忆特征值提取方面,利用传统的磁场梯度K值可以有效检验应力集中部位,同时本文提出一种新的基于磁记忆信号能量的检测特征值,实验证明可以通过此特征值对试样的安全性做出检测及评估.     

Interface Effect on the Dynamic Stress around an Elliptical Nano-Inhomogeneity Subjected to Anti-Plane Shear Waves

In the design of advanced micro- and nanosized materials and devices containing inclusions, the effects of surfaces/interfaces on the stress concentration become prominent. In this paper, based on the surface/interface elasticity theory, a two-dimensional problem of an elliptical nano-inhomogeneity under anti-plane shear waves is considered. The conformal mapping method is then applied to solve the formulated boundary value problem. The analytical solutions of displacement fields are expressed by employing wave function expansion method, the expanded mode coefficients are determined by satisfying the boundary conditions at the interfaces of the nano-inhomogeneity. Analyses show that the effect of the interfacial properties on the dynamic stress is significantly related to the wave frequency of incident waves, the shear modulus ratio of the nano-inhomogeneity and the matrix, and the dimensions of the elliptical nano-inhomogeneity. Comparison with the previous results is also presented.     

Determination of Stress Concentration Factors for Holes in Cylinders Using Thermoelastic Stress Analysis

Thermoelastic stress analysis is used to obtain the stress concentration factors (SCFs) from a variety of circular holes in cylinders. The cylinders are loaded in uniaxial tension, uniaxial compression and a combination of bending and compression. Firstly, radial holes are investigated and the results from the thermoelastic data obtained by the SPATE equipment are compared with previous experimental and numerical work. SCFs are then obtained from offset, oblique and offset–oblique holes using the Deltatherm system. The effect of hole obliquity and direction of applied load relative to the hole geometry are discussed in detail. Finally, the results from the cylinders are compared with predictions of the SCFs in cylinders from a previous study of oblique holes in flat plates.     

Study of Evaporative Convection in an Open Cavity under Shear Stress Flow

When a layer of volatile liquid is exposed to a shear flow of inert gas, thermal patterns, in the form of interfacial ripples and bulk plumes, are created by the combined action of evaporative, shear-driven and surface-tension-driven instabilities. The topology of the interfacial thermal patterns is mainly influenced by the geometry of the evaporating surface, the thickness of the evaporating layer, the intensity of the shear flow and by the physic-chemical properties of the working fluid. In this paper, by means of numerical simulations, we focused our attention on the dynamics of the interfacial thermal patterns for different working fluids and thicknesses of the volatile liquid layer. This study has been performed in the frame of the ESA sponsored Space Program on heat and mass transfer CIMEX-1. The choice of the fluids—ethyl alcohol and FC72 (n-perfluorohexane)—the reference values for the inert gas flow rate, the thickness of the liquid layer as well as the geometrical features of the computational domain correspond exactly to the ones foreseen for the CIMEX-1 experiment. However, the main conclusions can be considered of more general validity.     

双重Hammerstein型积分方程正解的存在性

利用锥理论,研究了一类新的双重Hammerstein型积分方程的正解的存在性.     

Experimental Study on Shear Localisation in Granular Materials Within Combined Strain and Stress Field

Abstract: The characteristic features of the shear zones formation in deforming granular materials were investigated using particle image velocimetry (PIV), which was combined with a photo‐elastic study of the stress field. Laboratory tests were performed for an active translation of rigid retaining wall. PIV is an optical technique for measuring displacement fields from successive digital images and was employed to analyse experiments on two different granular materials, composed of (1) sand grains and (2) glass granules. The tests on glass granules were supplemented by taking photo‐elastic images in circularly polarised light to gather information on changes in the average stress field, accompanying the specimen deformation. Attention was focused on the effect of the initial density, grain coarseness and magnitude of wall displacement on shear localisation within a strain field and its geometrical relation to some structures found in the stress field.     

积分平均法与偶数阶带阻尼项非线性微分方程的振动准则

用积分平均法和黎卡提技巧,对偶数阶带阻尼项非线性微分方程研究获得一些新的振动准则,这些结果改进和推广了一些已有文献的性质.最后,我们给出实例以阐述本文结果的有效性.     

论Helmholtz方程的一类边界积分方程的合理性

本文导出了Helmholtz 方程超定边值问题有解的一个充要条件,和用非解析开拓法证明了文[1]中的Helmholtz 方程在外域中的解的边界积分表示式的合理性,并将此类边界积分表示式推广用于带空洞的有限域。这样就比较严密而又浅近地证明了基于该表示式建立起来的间接变量和直接变量边界积分方程的合理性。     

Failure Rate Estimation from Field Data under Time‐Varying Stress

A model to assess the failure rate of equipment under use conditions is proposed. This model links noncontrolled variables to a piecewise failure rate combined with a proportional hazard model. Two influential variables are considered. One is the temperature characterizing the outdoor climate, and the other one is moisture—as an intrinsic variable. The maximum likelihood estimates of the model parameters are obtained. The efficiency of the method is evaluated through simulated data. Results on data from the field are provided. Copyright © 2012 John Wiley & Sons, Ltd.     

多角形域上第一类边界积分方程的高精度配置法

本文提出了一种多角区域上的第一类边界积分方程的高精度算法离散之前采用特殊周期变换,消去边界积分方程未知函数在积分端点的奇异性,然后使用常元配置法求解.该方法在内点获得超收敛O(h3).此外,通过Richardson整体外推,可进一步提高内点解的精度.实际计算结果表明,该方法优于同一问题的Galerkin方法甚至机械求积法.