A Non-linear Algorithm of Photoelastic Tomography for the Axisymmetric Problem

A non-linear algorithm of photoelastic tomography for the measurement of axisymmetric stress fields has been elaborated. It is free of any assumptions concerning the value of the birefringence or rotation of the principal stress axes along the light rays. The algorithm is based on the measurement of characteristic directions and phase retardation in two parallel sections of the test object. Stress components are presented in the form of power series along the radial coordinate. A differential evolution algorithm has been used for finding the stress field parameters, which fit the measurement data best. Application of the method is illustrated by residual stress measurement in a drinking glass.     

A mechanics prediction of the behaviour of mono-crystalline silicon under nano-indentation

This paper uses a new constitutive model developed recently by the authors to analyse the multi-phase transformations in mono-crystalline silicon when subjected to nano-indentation. The finite element method is employed to the integration of the stress–strain relationship. A very good agreement is reached with the experimental measurements, with an accurate prediction of the observed pop-in and pop-out and detailed phase transformation events in loading and unloading. It was found that due to the change of microstructures, the material in the deformation zone could experience a local unloading during indentation loading or undergo a local loading during indentation unloading. The phase transformation events during indentation are closely related to the variation of both the deviatoric and hydrostatic stress components.     

A Discrete Algorithm of Integrated Photoelasticity for Axisymmetric Problems

By measuring stresses in cylinders with no stress gradient in axial direction, the cross-section of the cylinder may be considered as consisting of concentric rings in each of which the stresses are constant. Axial stress distribution in the cylinder is determined stepwise starting with the outermost ring (the so-called onion-peeling method). This paper generalizes the onion-peeling method for the case of axisymmetric stress distributions when stress gradient in the axial direction is present. Measurement of the integrated isoclinic and optical retardation is carried out in two parallel sections which are perpendicular to the specimen axis, Δz apart from each other. The distributions of the axial stress and shear stress are determined directly from the measurement data, using linear approximation of integrated photoelasticity. Other stress components are determined using the equilibrium equation and the compatibility equation (if stresses are due to external loads) or using the generalized sum rule (if residual stresses in glass are measured). The method is less sensitive to measurement errors than the Abel inversion. In comparison with the polynomial approximation of the stress distributions, the onion-peeling method gives more adequate results if stress distribution is not smooth. The paper is illustrated with several applications.     

Finite strip buckling analysis of curved plate assemblies under biaxial loading

A finite strip method is presented for calculating the linear buckling stresses of structural assemblies of long, thin plate components which, in general, are curved and which are rigidly joined together at their longitudinal edges. It is assumed that on buckling under the action of a biaxial direct stress field the perturbation forces and displacements all vary sinusoidally in the longitudinal direction. A stiffness matrix relating the amplitudes of the perturbation forces and displacements is developed for the curved strip on the further assumption of relatively high-order polynomial variations of the displacement components around the plate width. Numerical results are presented of the application of the curved strip in calculating the buckling stresses of plates, cylinders, panels and formed sections.     

Penny-shaped crack in transversely isotropic piezoelectric materials

Using a method of potential functions introduced successively to integrate the field equations of three-dimensional problems for transversely isotropic piezoelectric materials, we obtain the so-called general solution in which the displacement components and electric potential functions are represented by a singular function satisfying some special partial differential equations of 6th order. In order to analyse the mechanical-electric coupling behaviour of penny-shaped crack for above materials, another form of the general solution is obtained under cylindrical coordinate system by introducing three quasi-harmonic functions into the general equations obtained above. It is shown that both the two forms of the general solutions are complete. Furthermore, the mechanical-electric coupling behaviour of penny-shaped crack in transversely isotropic piezoelectric media is analysed under axisymmetric tensile loading case, and the crack-tip stress field and electric displacement field are obtained. The results show that the stress and the electric displacement components near the crack tip have (r ^−1/2) singularity. The project supported by the Natural Science Foundation of Shaanxi Province, China     

热-机载荷下不规则夹杂的奇异性应力场分析

基于有限元特征分析法得到的夹杂角部场数值特征解开发了一种超级奇异单元模型,并将其与普通四节点单元紧密结合,用于热-机载荷下夹杂角端部的应力场分析。在数值计算中,考察了热-机载荷下不同弹性比和不同夹杂尺寸的应力强度因子,并将所得结果与文献解和传统有限元方法解比对。结果表明,本文方法对热-机耦合条件下的不规则夹杂角端部的热弹性应力分析极为有效,可避免局部网格的高度加密,并提高计算效率。模型在复合材料夹杂的局部强度问题分析方面具有很好的实用性。     

具有随机参数的含裂纹板弯曲应力强度因子的统计分析

本文首次应用随机有限元法研究了具有随机参数的含裂纹板裂纹尖端弯曲应力强度因子的统计性质。文中首先给出了杂交模式的裂纹尖端奇异单元的刚度矩阵,然后基于随机场的局部平均理论和一阶泰勒展开得到了应力强度因子均值和方差的计算公式。作为数例,详细讨论了杨氏模量、泊松比及板厚度的不确定性对应力强度因子的影响。     

含中心裂纹任意截面柱体扭转时的应力强度因子计算

本文提出了一组应力函数,采用边界配置方法计算了含中心裂纹不同截面形状柱体扭转时的应力强度因子。有关椭圆截面柱体的算例表明,本文方法具有良好的精度。同时,文中给出了圆、椭圆和矩形等不同截面柱体的计算结果。     

Laser Doppler velocimetry measurements in an interior flow test facility: A database for CFD-code evaluation

Measurements in a test facility for a complex interior flow are provided as a database for CFD code evaluation. For pure forced convection as well as to a minor extent also for mixed convection flows, the three time-averaged components of the velocity vector and all components of the Reynolds stress tensor are measured in selected cross sections. Special attention is given to the inflow into the main flow section, since it is the important part of the boundary condition for a numerical solution.     

Evaluation of Residual Stresses Induced by Robotized Hammer Peening by the Contour Method

Welded components suffer from high tensile residual stresses close to the weld beads. These stresses seem to be the origin of premature cracking which could result in a catastrophic rupture during operation and a reduction of the lifespan of these components. In this context, the Hydro-Québec’s Research Institute (IREQ) developed a technique of residual stresses relaxation by robotized hammer peening which makes it possible to release stresses close to surface and preserve the mechanical and dimensional properties of manufactured components. Robotized hammer peening was used to induce compressive residual stresses on initially stress free samples of austenitic stainless steel 304L. Hammer peening layers from one to nine were performed and the resulting residual stresses were evaluated thanks to the contour technique. Complete 2D residual stress fields on samples cross sections were obtained. The ability of hammer peening to relax residual stresses within welded plates was then quantified on austenitic stainless steel 304L plates welded with a 308 steel and hammer peened. These tests show the efficiency of hammer peening as a method to relax tensile residual stresses and induce compressive ones to a depth of a few millimetres. Process parameters were optimized such as the number of hammer peening layers to be applied to reduce processing time and maximization of the intensity and spatial distribution of the compressive residual stresses.     

基于子模型法的大跨斜拉桥扁平钢箱梁应力分析

为了掌握扁平流线型钢箱梁应力水平及其分布,本文以润扬斜拉桥为工程背景,建立了整体有限元模型和局部有限元子模型。在对整体有限元模型进行分析的基础上,应用子模型法对润扬斜拉桥主梁各关键截面进行了有限元受力分析,运用试验结果验证了有限元结果的可靠性。在此基础上研究了主梁各关键截面的应力水平及其分布特点,并进一步总结了试验荷载下润扬斜拉桥扁平钢箱梁的受力特点。结果表明了子模型法应用于扁平钢箱梁局部应力分析的有效性和可靠性,其结果可为润扬斜拉桥扁平钢箱梁的安全监测提供科学依据。     

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅲ)-CALCULATION FOR C-SHAPED BELLOWS

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一种散光图象双折射相移的方法

由Pindera等提出了等达因法导出了平面问题的三个应力分量，可以非破坏性测取受力物体内部的应力状态，是一种有效的光测技术，应力分量与等达因条纹级次的导数相关，为得到具有高测试精度的应力分量在等达因条纹测试中引入了双折射相移技术，文中提出了一种在散光激光入射光路中用加入一可调偏振片和一可调1／4波片实现散光图象双折射相移的方法，该方法设备简单，能保证总体光强的一致性。     

Residual stresses in silicon-on-sapphire thin film systems

This paper uses the finite element method to analyse the generation and evolution of residual stress in silicon-on-sapphire thin film systems during cooling. The effects of material properties, thin film structures and processing conditions, on the stress distribution were explored in detail. It was found that under certain conditions, significant stress concentration and discontinuity can take place to initiate crack and/or delamination in the systems. However, these can be minimised by controlling the buffer layer thickness.     

钢筋砼叠合梁受力特性分析

本运用成熟的电算模拟方法,计算得到二阶段受力钢筋砼叠合梁在不同受力阶段的截面应力分布规律及钢筋的应力变化规律,分析得到二阶段受力时钢筋砼叠合＾「１」的受拉钢筋应力超前,受压区砼应变迟后逐渐缓解的实质为截面应力重分布的结果。     

Fracture mechanics based design procedures for pressurized components having part-through cracks

This paper presents a fracture mechanics based design procedure for pressurized components having part-through cracks. Fracture critical stresses are evaluated for the assumed crack configurations and the fracture envelopes are obtained for these configurations. For small size crack configurations, Feddersen's type correction is made for proper estimation of critical stress values. Residual strength of unbroken ligament is a more appropriate criterion for the design of thin sections with parth-through cracks. A criterion based on the ligament failure is defined for cases where the critical fracture stresses are above the material yield stress value. The procedure is illustrated by presenting an example of a pressurized tankage used in aerospace industry.     

复杂三维结构物的光弹性实验研究

应用光弹性原理和方法，根据有关相似原理，对研究对象的几何尺寸进行缩比、模型设计及加工成型．然后将模型在危险载荷作用下，进行应力冻结、切片及应力分析．确定了模型不同截面上的应力及其变化规律，为优化设计和调整数值计算方法提供了有价值的依据．     

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅲ)-CALCULATION FOR C-SHAPED BELLOWS

This is one of the applications of Part (I), in which the angular stiffness, the lateral stiffness and the corresponding stress distributions of C-shaped bellows were calculated. The bellows was divided into protruding sections and concave sections for the use of the general solution (I), but the continuity of the stress resultants and the deformations at each joint of the sections were entirely satisfied. The present results were compared with those of the other theories and experiments, and are also tested by the numerically integral method. It is shown that the governing equation and the general solution (I) are very effective. Contributed by HUANG Qian Biography: ZHU Wei-ping (1962-)     

微粘结实验影响因素的边界元法分析

微粘结实验是一种新的简便的测量复合材料界面剪切强度的方法，本文运用数值方法－边界单元法，对一个实际试件进行了界面应力计算，讨论了材料常数，刀口宽度和新月尖角三种主要因素对界面应力分布可能产生的影响，从而为实验结果分析，实验方法改进和评估提供依据。     

Electronic techniques in isodyne stress analysis: Part 1. Basic relations

The purpose of the study was to develop electronic techniques for collecting, processing and evaluating information in experimental isodyne stress analysis. The original technique involved chemical photography recording and manual evaluation of the normal and shear isodyne functions and their derivatives, which are proportional to the stress components. One objective of the reported study was to show that it is feasible to reliably reconstruct isodyne surfaces which contain information on the internal force intensities and the components of the stress tensor. It is shown that the new technique satisfies all the theoretical conditions and constraints imposed by the theory of the analytical and optical isodynes. Thus another objective of the reported study was to demonstrate that the isodyne stress analysis allows one to obtain reliable data on the actual three-dimensional stresses in a cost-effective manner. The procedure developed to date and presented in the paper is a hybrid electronic-manual procedure. It involves electronic recording of the isodyne fields, manual determination of the isodyne orders in chosen sections, and electronic determination of the indicated and load-induced isodyne functions and of the isodyne surfaces. It is shown that the developed techniques are more reliable, accurate and cost-efficient than the traditional techniques of photomechanics. Pertinent data are illustrated by examples presented in Part 2.