Phase-Stepping Photoelasticity by Use of Retarders with Arbitrary Retardation

The present paper describes a new phase-stepping algorithm for the analysis of isochromatics and isoclinics using retarders with arbitrary retardation. A retarder used in the proposed method is not necessarily a quarter-wave plate specified for the wavelength of the light used. Not only the isochromatic and isoclinic parameters but also the retardation of the input and output retarders are determined simultaneously by the proposed phase-stepping method. Thus, accurate analysis can be performed by the proposed method even if accurate quarter-wave plates are not used. In addition, any wavelength of visible light can be used in a single polariscope without requiring matching the wavelength of the quarter-wave plate. Thus, a multi-wavelength technique is easily combined with the proposed method for accuracy improvement, phase-unwrapping, or correction of ambiguity.     

结构强度在线分析的光电复合法

本文将电测方法与光弹性方法结合在一起,导出了应用读数应变εd就可以获取准静态情况下结构的载荷P,危险截面位置和最大应力峰值σmax(X0Y0Z0)的理论计算方法,从而为结构的在线强度评价提供一种实验分析方法,文中导出的εd-t,P-t,k-t及σ－t诸曲线谱的相关性理论,不仅揭示了εd与未知载荷P,无量纲应力系数K及应力σ之间的关系,更重要的是这种分析思想与计算机技术结合在一起,可以达到设备强度自动报敬警的作用,作为一个实例,作者应用本理论成功地解决了某钢厂热轧线上一个粗轧机机架在线的应力强度评价难题。     

A physical decomposition of the stress tensor for complex flows

Traditionally, the components of the stress with respect to a relevant coordinate system are used for the purpose of stress visualisation and interpretation. A case for using a flow dependent measure to interpret and visualise stress is made for two dimensional flow, together with a suggestion for extending the idea to three dimensions. The method is illustrated for Newtonian and Oldroyd B fluids in both the eccentrically rotating cylinder and flow past a cylinder benchmark problems. In the context of a generalised Newtonian fluid, the relation between the flow-dependent stress measure to other field variables under certain flow conditions, is examined and is indicative of its importance in complex flow.

X-Ray diffraction evidence for the role of stacking faults in plastic deformation of solids under shock loading

A mechanism responsible for the high speed shear relaxation immediately behind shock fronts is suggested. The shear stress generated by the shock front causes the growth of two-dimensional defects in the crystal lattice, known as stacking faults (SF). Increasing the SF concentration and area leads to the absorption of impact energy. A breach of the lattice symmetry due to the SF presence causes an additional shift in peaks of the x-ray diffraction pattern obtained from the shock compressed material. Thus pulse x-ray diffraction is the only method that experimentally measures both the dilatational and deviatoric components of the deformation, which takes place during shock wave passage.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

图像相关法在高分子材料拉伸性能研究中的应用

本文对聚碳酸酯(PC)和丙烯腈丁二烯苯乙烯(ABS)的合金(PC/ABS)高分子材料不同环境温度下的拉伸性能进行了试验研究。根据图像相关分析法编制了图像法位移测量分析软件,并对该分析软件的适用性进行了分析。系统研究了PC/ABS高分子材料拉伸试验时三个方向的位移场和应变场。根据测得的位移场研究了该高分子材料拉伸过程中应变和应变率的变化以及应力应变变化规律,并对试验结果进行了详细分析。结果表明,文中采用的图像法位移测量系统具有较高的测试精度;拉伸过程中,试件厚度方向的收缩变形大于宽度方向的收缩变形;颈缩过程区具有非常高的应变率,颈缩后的平直颈缩区的应变率快速下降到一个很低的应变率继续缓慢变形;尽管载荷位移曲线出现了较大的载荷下降现象,PC/ABS拉伸时的真应力应变曲线没有明显的应力下降现象出现,因此,载荷下降现象主要由颈缩时的截面减小引起;高分子材料PC/ABS的屈服应力随环境温度的升高而降低。     

Supercritical equilibrium solutions of axially moving beams with hybrid boundary conditions

In this paper supercritical equilibria and critical speeds of axially moving beams constrained by sleeves with torsion springs are deduced. Transverse vibration of the beams is governed by a nonlinear integro-partial-differential equation. In the supercritical regime, the corresponding static equilibrium equation for the hybrid boundary conditions is analytically solved for the equilibria and the critical speeds. In the view of the non-trivial equilibrium, comparisons are made among the integro-partial-differential equation, a nonlinear partial-differential equation for transverse vibration, and coupled equations for planar motion under the hybrid boundary conditions.     

光弹性等倾线获取的图像处理技术

提出一种对数微分法,有效地解决了光弹性实验中等倾线的提取问题,不仅可消除平面偏振光场中等差线对等倾线的影响,而且能高精度地提取任意复杂受力模型等倾线.最后给出了等倾线提取及精度分析的两个实例,实验证明;本方法具有广阔的应用前景.     

Nonlinear analysis of beam–column joints using softened truss model

The aim of this study is to expand the application of the nonlinear softened truss model for membrane elements on beam–column joints. The softened truss model employs three equations for equilibrium, three for compatibility and four equations for the constitutive laws of materials. The constitutive equations for both the concrete and steel are based on the actually observed stress–strain relationships. The model has three important attributes. The first is the nonlinear association of stress and strain. The second, and conceivably more noteworthy, is the softening of concrete in compression due to tensile strains in the perpendicular direction. The third is that the influence of the concrete tensile stresses between cracks on the average stress–strain relationship for reinforcing steel and the influence of orthogonal tensile stresses on the compression stress–strain relationship for concrete can be considered in the model. For beam–column joints, one of the most important factors influencing the behaviour is certainly the bond conditions of the beam bars. In this study, the softened truss model is expanded to take into account the influence of this important factor into account. In the revised version of the model, full strain compatibility does not exist between the steel reinforcement and the surrounding concrete and thus the factors influencing the bond-slip between concrete and reinforcement is adequately considered. The improved softened truss model is applied on 51 exterior beam–column joint tests. It is apparent from the results that the revised model gives very accurate predictions of the shear strength of joints and is an improvement on the existing version of the model proposed by Hsu.     

三维光弹性中预应力结构的应力冻结研究

本文提出用三维光弹性应力冻结法模拟分析预应力钢筋混凝土结构中的应力。通过模拟体与实体结构的相似性研究,给出了模型载荷比例系数Cq参数,通过参数合理的选取,有效的解决了应力冻结水平预测这一技术关键;用光弹性应力二次冻结法,将结构预应力和负载应力冻结在同一试件中;应分析精度对模型尺寸的要求,采用了精密浇铸的方法制作模型。此外,还研制了受力清晰明确的加载系统。对这些涉及应力冻结的若干关键问题结合工程实例进行探讨。实验应力分析结果与有限元数值法一致性较好。     

Numerical Investigation of Large Elastoplastic Strains of Three-Dimensional Bodies

A method of stress—strain analysis of elastoplastic bodies with large displacements, rotations, and finite strains is developed. The incremental loading technique is used within the framework of the arbitrary Lagrangian—Eulerian formulation. Constitutive equations are derived which relate the Jaumann derivative of the Cauchy—Euler stress tensor and the strain rate. The spatial discretization is based on the FEM and multilinear three-dimensional isoparametric approximation. An algorithm of stress—strain analysis of elastic, hyperelastic, and perfectly plastic bodies is given. Numerical examples demonstrate the capabilities of the method and its software implementation __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 6, pp. 36–43, June 2005.     

FJ662A公路客车骨架的脆漆和静态电测试验分析

本文介绍用脆漆法和电测法测定和分析车身骨架强度的方法及结果、并讨论使用这两种方法相辅相成的关系。     

Non-linear elastic non-uniform torsion of bars of arbitrary cross-section by BEM

In this paper an elastic non-uniform torsion analysis of simply or multiply connected cylindrical bars of arbitrary cross-section taking into account the effect of geometric non-linearity is presented employing the boundary-element(BE) method. The torque-rotation relationship is computed based on the finite-displacement (finite-rotation) theory, that is the transverse displacement components are expressed so as to be valid for large rotations and the longitudinal normal strain includes the second-order geometric non-linear term often described as the “Wagner strain”. The proposed formulation does not stand on the assumption of a thin-walled structure and therefore the cross-section's torsional rigidity is evaluated exactly without using the so-called Saint-Venant's torsional constant. The torsional rigidity of the cross-section is evaluated directly employing the primary warping function of the cross-section depending on its shape. Three boundary-value problems with respect to the variable along the beam axis angle of twist, to the primary and to the secondary warping functions are formulated. The first one, employing the Analog Equation Method (a BEM-based method), yields a system of non-linear equations from which the angle of twist is computed by an iterative process. The remaining two problems are solved employing a pure BE method. Numerical results are presented to illustrate the method and demonstrate its efficiency and accuracy. The developed procedure retains most of the advantages of a BEM solution over a pure domain discretization method, although it requires domain discretization.     

薄膜涂层材料界面纯剪破坏标准试验法的开发

界面强度是薄膜涂层材料的最重要的性能指标之一，目前尚缺乏有效的测量方法。测量界面强度的主要困难在于寻求一种便于试验的试件形状和加载方式，使得界面上能够产生不同的应力状态，即在不同的剥离应力和剪应力比的状态下发生破坏。本文采用有限元数值分析（ABAQUS），研究了几种具有简单几何形状的试件的界面应力，并基于大量的数值试验，设计了剪应力为破坏支配因素的试件形状和加载方式，并且给出了便于应用的最大界面剪应力的经验估算公式。该经验公式可以适用于各种材料组合和薄膜涂层的厚度。研究结果表明，通过对薄膜涂层材料试件的基体引入缺口以产生应力集中，进行普通的四点弯曲试验，可以进行剪应力占支配地位的界面破坏试验。利用本文提出的试件形状和相应的最大界面剪应力经验公式，可以通过破坏试验简单地得到界面的剪切强度。     

An Accurate Solution of the Poisson Equation by the Finite Difference-Chebyshev-Tau Method

ＩｎｔｒｏｄｕｃｔｉｏｎＭａｎｙｓｃｈｏｌｏｒｓｈａｖｅｄｉｓｃｕｓｓｅｄｔｈｅｓｏｌｕｔｉｏｎｏｆｔｈｅｔｗｏ＿ｄｉｍｅｎｓｉｏｎａｌＰｏｉｓｓｏｎｅｑｕａｔｉｏｎ .ＡｍａｔｒｉｘｄｉａｇｏｎａｌｉｚａｔｉｏｎｍｅｔｈｏｄｗａｓｄｅｖｅｌｏｐｅｄｂｙＨａｉｄｖｏｇｅｌａｎｄＺａｎｇ[1]ｆｏｒｔｈｅｓｏｌｕｔｉｏｎｏｆｔｈｅｔｗｏ＿ｄｉｍｅｎｓｉｏｎａｌＰｏｉｓｓｏｎｅｑｕａｔｉｏｎ .Ｔｈｉｓｍｅｔｈｏｄｉｓｅｆｆｉｃｉｅｎｔｂｕｔｒｅｑｕｉｒｅｓａｐｒｅｐｒｏｃｅｓｓｉｎｇｃａｌｃｕｌａｔｉｏ…     

随机结构静力反应概率密度演化方程的差分方法

随机结构分析的概率密度演化方法是分析随机结构静力反应的一种具有良好前景的方法。本文研究了求解随机结构静力反应概率密度演化方程的差分方法，分别探讨了单边差分格式和Lax-Wendroff格式的计算性态。二者均能满足概率相容性条件并且能够保证均值线性增长。以八层框架结构的静力随机反应为例，对两种差分格式的结果及精确解答进行了具体的比较分析。研究表明，两种差分格式均是收敛和稳定的，在不连续点处存在角点效应．单边差分格式能够保证概率非负性，而Lax-Wendroff格式具有往往更快的收敛速度。就变异系数而言，通常单边差分格式的变异系数随着区间离散数的增长而趋于稳定值，Lax-Wendroff格式则一开始就可得到恒定的值。     

Instabilities in shear and simple shear deformations of gold crystals

We use the tight-binding potential and molecular mechanics simulations to study local and global instabilities in shear and simple shear deformations of three initially defect-free finite cubes of gold single crystal containing 3480, 7813, and 58,825 atoms. Displacements on all bounding surfaces are prescribed while studying simple shear deformations, but displacements on only two opposite surfaces are assigned during simulations of shear deformations with the remaining four surfaces kept free of external forces. The criteria used to delineate local instabilities in the system include the following: (i) a component of the second-order spatial gradients of the displacement field having large values relative to its average value in the body, (ii) the minimum eigenvalue of the Hessian of the energy of an atom becoming non-positive, and (iii) structural changes represented by a high value of the common neighborhood parameter. It is found that these criteria are met essentially simultaneously at the same atomic position. Effects of free surfaces are evidenced by different deformation patterns for the same specimen deformed in shear and simple shear. The shear strength of a specimen deformed in simple shear is more than three times that of the same specimen deformed in shear. It is found that for each cubic specimen deformed in simple shear the evolution with the shear strain of the average shear stress, prior to the onset of instabilities, is almost identical to that in an equivalent hyperelastic material with strain energy density derived from the tight-binding potential and the assumption that it obeys the Cauchy-Born rule. Even though the material response of the hyperelastic body predicted from the strain energy density is stable over the range of the shear strain simulated in this work, the molecular mechanics simulations predict local and global instabilities in the three specimens.     

边界元和激光散斑的子域杂交法

本文将计算力学的边界元法和实验力学的激光散斑法相结合用于求解受力物体的应力应变场。即用实验提供变形物体的真实边界条件,用数值方法进行求解。文中定义了虚边界的概念,并进一步提出了子域杂交法。同单纯数值计算和实验分析相比较,本文提出的方法无需构造力学模型,因而具有简单、可靠的特点,并可以更好地应用于实际问题。     

Explicit finite-difference procedures for elastodynamic analysis of layered media

Summary Explicit finite-difference procedures are proposed to simulate the elastodynamic response of layered media. To avoid large numerical dispersion and dissipation, different grid sizes are used for different material layers so that the CFL number in each layer can be set to one in the limit. The master-slave technique is applied to deal with the mismatch of grids along the material interface. The interface can be either bonded or unbonded. The dynamic contact between two layers along an unbonded interface is also considered. Numerical examples are presented. Received 4 August 1997; accepted for publication 24 April 1998     

用数理统计方法评定电阻应变计灵敏系数的精度等级

本文采用大子样、小子样抽样理论的数理统计方法,评定电阻应变计灵敏系数的精度等级。     

Simulation of 2D external viscous flows by means of a domain decomposition method using an influence matrix technique

Two-dimensional external viscous flows are numerically approximated by means of a domain decomposition method which combines a vortex method and a finite difference method. The vortex method is used in the flow region which is dominated by convective effects, whereas the finite difference method is used in the flow region where viscous diffusion effects are dominant. An influence matrix technique combined with the uniformity condition of the pressure is used to enforce the tangential velocity boundary condition. Comparisons between numerical and experimental data show that the method is well adapted for simulating two-dimensional flows.