基于DSCM-FEM的花岗岩力学参数反演方法研究

开展了基于数字散斑相关方法和有限单元法(DSCM-FEM)的花岗岩力学参数反演方法研究.选取一种花岗岩进行三点弯曲实验,以数字散斑相关方法作为实验观测手段,分析得到的试件加载过程中表面位移场作为测量值,通过有限元法得到的位移场作为仿真值,以测量值与仿真值之间的误差作为目标函数,构建反问题模型,利用优化算法对岩石的弹性模...     

关于负泊松比的材料力学课程教学拓展与探索

泊松比是材料力学课程教学中的重要力学概念与材料弹性常数之一。本文对现有材料力学课程中泊松比教学内容进行了拓展和补充,引入了负泊松比效应概念,并介绍了常见的负泊松比材料及其力学性能优势。重点基于内凹蜂窝超材料,详细介绍了实现负泊松比效应的超材料力学理论分析及其教学实践;并借鉴虚拟仿真实验概念,应用有限元数值分析方法,对超材料的负泊松比效应进行仿真分析与讨论,直观地展示了超材料的力学变形模式及其负泊松比效应。从而以此为切入点,加深学生对弯曲内力、挠度、应变和泊松比等重点知识的理解与实践运用。     

基于数字图像相关方法的材料力学实验教学探索

实验教学是培养学生实践和创新能力的重要手段,如何在有限的实验学时条件下,开展丰富高效的力学实验、关联更多的理论知识点是材料力学教学改革亟需解决的问题。本文引入数字图像相关（digital image correlation, DIC）方法,以带孔低碳钢拉伸和高温镍基合金热变形测量等试验为例,对材料力学实验教学进行改革探索。实践表明,基于DIC方法的实验教学可充分发挥出DIC全场变形可视化、测量过程简单、快速精确等优势,显著调动了学生的学习兴趣,加深了学生对多个关联知识点的理解,同时启迪了学生的科学创新意识。     

基于光纤传感器的固体杨氏模量与泊松比测量方法研究

提出了一种基于光纤传感器的测量固体材料杨氏模量与泊松比的方法,给出了Sagnac光纤干涉仪的环形光纤作为点传感器检测声波及用于声速测量的原理,推导出固体中声波速度与材料的杨氏模量及泊松比的关系式.以光纤Sagnac干涉仪作为传感器贴附于三角铸铁导轨表面,分别测出声表面波与纵波的速度,根据理论推导,得到了铸铁的杨氏模量与泊松比.实验结果与理论数值基本吻合,表明了此测量方法的可行性,为固体材料性能评估提供了一种新的方法.     

数字图像相关分析法增量位移场测试技术

利用位移场的连续性,对亚像素位移场的算法进行了一些改进,设计了一套分步计算位移场、应变场的测量计算方法,较好地解决了数字图像相关分析法计算精度和效率.采用增量位移场叠加的方法计算大应变位移场,采用局部平面拟合的方法计算应变场.通过对高分子材料拉伸试验位移场的测量和结果标定,说明该方法具有较强的实用性和计算精度.同时,由于避免了对亚像素点的搜索,大大提高了计算效率.     

悬臂梁弯曲共振法自由阻尼结构试件设计研究

用悬臂梁弯曲共振法测量阻尼材料动态力学参数时,试件设计是否合理直接决定了测量结果的可信度.考虑到复合试件基底层材料阻尼的影响,本文对测量理论进行了改进,得到了考虑基底层阻尼影响的悬臂梁弯曲共振法测量方程.仿真结果表明忽略基底层阻尼将会导致杨氏模量和损耗因子测量精度降低,并且损耗因子测量误差对基底层阻尼变化更敏感.这为基底材料的选用提供了一定的理论依据.本文还结合误差放大因子的概念,对试件设计若干关键参数进行了灵敏度分析,得到了一组对悬臂梁弯曲共振法自由阻尼结构试件设计具有指导意义的结论.     

基于三相球模型确定泡沫塑料有效模量

通过复合材料三相球模型确定泡沫塑料的体积模量、剪切模量、杨氏模量和泊松比等材料等参数与材料孔隙比的关系，并将该文结果同微分法得到的结果进行了对比；结果表明：三相球模型确定的材料参数在相同孔隙比情况下，一般都高于微分法确定的结果，两种方法得到的有效剪切模量和杨氏模量差异较小，而体积模量和泊松比则差异较大，然而，由三相球模型确定的泡沫塑料杨氏模量仍可与实验较好地符合。此外，该文结果也同现有的理论及实验     

综述:阵列式高速摄像技术及其在动态光测力学中的应用

高速摄像技术与先进光测力学方法相结合是研究材料和结构断裂、冲击、爆破、渗透等动态力学行为的重要手段。阵列式高速摄像系统是一种具有成像通道成阵列均匀分布显著特点的高速摄像系统,已在科学研究和工程技术领域得到广泛应用。本文对阵列式高速摄像系统的设计及其动态光测力学方面的应用进行综述。首先,对阵列式高速摄像系统的发展历史和技术改进过程进行概述。其次,阐述阵列式高速摄像系统的研究现状,重点介绍双场镜、旋转镜面和物理分幅等三类典型阵列式高速摄像系统的设计原理,并对不同系统的主要技术指标进行总结。再次,对阵列式高速摄像系统光学视差的定性和定量分析方法进行总结,并对视差修正方法进行归纳。最后,结合光弹法、焦散线法、数字图像相关法、云纹法、相干梯度敏感法和数字梯度敏感法等主要光测实验技术,阐述阵列式高速摄像系统在动态光测力学领域中的应用。本文对阵列式高速摄像系统的设计和应用进行了总结和展望,对于研制动态光测力学设备、推动材料与结构动态力学行为以及阵列高通量测试的基础科学问题的创新性实验研究具有一定参考意义。     

球形薄膜的变形测量与力学分析研究

目前对于薄膜材料力学性能研究多采用单轴拉伸的实验方法,此方法在测量有特殊构型薄膜材料时有一定误差,也只能测量单一方向的力学性能。本文选用球面乳胶薄膜为实验材料,在考虑球形外形结构的基础之上,测量了整个薄膜表面的力学性能。实验在自制的装置之上结合三维数字图像相关技术(3D-DIC)测出整个薄膜表面位移场,并且结合相关公式计算出乳胶球面薄膜制品表面的拉格朗日应力场和应变场,并对膨胀后薄膜厚度变化做了相应分析。结果显示乳胶薄膜表面的变形并非均匀,圆周方向抗变形能力大于子午线方向。     

一种由圆柱体试件的侧向压缩力-位移关系同时测量材料弹性模量和泊松比的新方法

材料的弹性模量和泊松比是材料表征的重要力学参数,传统的压缩试验需要同时测量荷载、压缩和横向变形,才能实现对弹性模量和泊松比的同时测量。本文从Hertz接触理论出发,推导出弹性圆柱体在侧向压缩下的位移-力关系公式,在该关系式中位移与力的关系除与试件的几何尺寸相关外,还取决于材料的弹性模量和泊松比。因此,可以通过对侧向压缩试验测得的力-位移关系进行非线性拟合,得到材料的弹性模量和泊松比。本文通过对硅胶材料开展轴向与侧向压缩试验,对比两种试验测量得到的弹性模量和泊松比,结果较为一致,验证了本文提出方法的可行性。对于模量较小的软物质,因加载过程的荷载常常较小,系统测量的位移可代表试件的变形位移,故本文提出的新测量方法特别适合应用于该类型材料的相关性能测量。     

旋转弹体表面红外辐射干扰补偿模型

针对地球红外辐射姿态测试方法中弹体表面红外辐射干扰较大的问题,建立旋转弹体自身红外辐射补偿模型,从而提高弹体姿态测量精度。首先,采用瞬态热平衡微分方程推导出旋转弹体表面温度变化曲线,获取弹体自身红外辐射亮度。然后,根据地球红外辐射及其在大气中的传播规律,建立了弹体自身红外辐射补偿数学模型。最终结合红外传感器输出和所推导的补偿模型,估算红外辐射补偿参数。结果表明补偿后姿态角解算误差显著降低,俯仰角和横滚角解算误差最终分别保持在±0.2°和±0.4°以内。本方法对姿态测量误差的减小具有显著效果,补偿方法简单有效,对旋转弹体的红外姿态测试技术的研究具有借鉴意义。     

基于遗传算法的混凝土三维非稳态温度场反分析

大体积混凝土结构施工期间的合理温度控制问题非常重要，而精确进行温度计算所需的一些材料参数往往不易直接测得，需要根据一些易测得的量进行反求。本文基于三维瞬态温度场有限元求解理论与反问题理论，建立了混凝土三维瞬态温度场反问题求解数值模型。运用遗传算法寻求非线性反演问题全局最优解，只需要若干点温度实测值便可实现混凝土多个热学参数如绝热温升、导温、导热系数及热交换系鼓等的同时反演，算例对本文反演方法的反演精度及数值稳定性给出了满意的证明。     

Determination of plastic stress-strain behavior by digital-image-processing techniques

This work explores the application of digitalimage-processing techniques to the measurement of large plastic strains. Two sample problems have been selected, namely the uniform tensile deformation of aluminum-sheet metal strips and the post-necking deformation of copper circular rods. Images of these gridded metallic test pleces were captured, digitized and analyzed in a fully computerized way to evaluate strain distributions, anisotropic parameters and plastic stress-strain flow curves. For post-necked test pieces, Bridgman stress correction has been easily applied by defining the neck profile contour from the automated processing of digitized images. Results compare satisfactorily with those based on displacements measured by conventional microscopy. The presented technique, with added improvements, can consititute a viable one for accurate and fully computerized measurement of large deformations.     

Experimental technique for measurement of stress-acoustic coefficients of Rayleigh waves

Two stress-acoustic coefficients,K ₁ andK ₂, are required to determine the state of biaxial surface stress from ultrasonic Rayleigh-wave velocity or time of flight measurements in elastic, initially isotropic solids. An experimental technique is described for the precise measurement of these two coefficients in uniaxially stressed test specimens. The technique is applied to aluminum 2024-T351 and 6061-T651 alloys. The influence on measurement results of various parameters such as material anisotropy and temperature is considered.     

Determination of Anisotropic Plastic Constitutive Parameters Using the Virtual Fields Method

The aim of the present study is to retrieve all the anisotropic plastic constitutive parameters from uniaxial loading. A complex geometry which can provide very heterogeneous stress states in a uniaxial tensile test was chosen for steel sheet specimens. A digital image correlation technique was used for the full-field heterogeneous strain measurement. The orthotropic Hill1948 yield criterion with Swift isotropic hardening was adopted as an elasto-plastic constitutive model. The virtual fields method (VFM) was employed as an inverse analytical tool to determine the constitutive parameters. All the parameters were successfully identified using the VFM by combining two tensile test results obtained in rolling and transverse directions.     

Surface Strain Measurements Using a 3D Scanning Laser Vibrometer

Three-dimensional scanning laser vibrometers enable extremely accurate non-contact measurement of the three-dimensional displacements on the surface of structures. This paper looks at the feasibility of using such a scanning laser vibrometer for the non-contact measurement of dynamic strain fields across the surface of a planar structure subjected to in-plane loading. Issues such as laser head alignment and choice of differentiation filter parameters are discussed. Finally, experimental results of two test specimens are presented which clearly demonstrate the significant potential of this new experimental technique as well as highlighting several limitations.     

Enhancement of heat transfer in compact heat exchanger by different type of rib with holographic interferometry

An experimental study was carried out to investigate enhancement of heat transfer in compact heat exchanger by keeping pressure drop constant in a given range. Two different test matrices, cylindrical and triangular, used to find the optimum ribs were compared with a smooth channel. The investigation was performed with both laminar and turbulent forced flow for Reynolds numbers from 250 to 7000. The geometric parameters, in order to satisfied manufacturer demands, were fixed at p/e=6.67 and the wall temperature was held constant at 50°C. The technique of holographic interferometry was used to determine the temperature distribution in the test duct. Velocity distribution was measured using laser doppler anemometer techniques. For comparison the technique of global measurement was also used. The results revealed that cylindrical ribs are optimum heat transfer for conversion of pressure drop. An 8% experimental error was found in global measurement compared to holographic interferometry.     

船用惯性系统试验安装标校与变形测量

船用惯性系统试验安装标校和变形测量是提高测量精度,保证试验质量的关键技术,因此在对设备的安装误差和船体变形造成的测量误差进行分析的基础上,重点阐述惯性系统试验零位对准和变形测量的相关理论和工程技术。     

Measurement of coatings' elastic properties by mechanical methods: Part 1. Consideration on experimental errors

A critical analysis of some mechanical methods employed for measuring the elastic properties of coatings is presented. A rational basis for properly choosing test methods, transducers and layer thicknesses is provided. The analyzed methods, usually applied to relatively thick coatings, include four-point bending tests and the resonance technique. General relationships for the evaluation of coatings' elastic properties, derived from the multilayer beam and plate theories, are discussed. On the basis of the error propagation theory, for different combinations of materials and layer thicknesses, the influence of typical experimental errors, test setup parameters and material properties is analyzed, and sensitivity coefficients for relative errors are discussed. The critical experimental variables and their effect on measurement accuracy are highlighted, suggesting suitable conditions for selecting specimen geometry and testing conditions. A procedure for measurement at high temperature is outlined.     

基于大型炉体焊接残余应力测试的盲孔法研究

为提高炉体焊接残余应力测试精度,对传统的盲孔法进行改进,即在测点打孔后多次扩孔并增加孔深;通过对SM400ZL钢焊接残余应力测试时的应变释放系数A,B进行实验标定,得出多组应变释放系数值,计算可得残余应力的估算值,并对不同状况下的残余应力值进行比较.通过大拉力标定试验得出SM400ZL钢盲孔的孔边塑性变形对测量精度的影响和塑性修正公式.结果表明,改进的盲孔法能够更准确地测得焊接残余应力值,测量结果经塑性修正,最大误差减小到2%以下.测试方法和结果可直接在相关的工程实际中应用.