云纹干涉法测定复合材料单孔连接件的应力场

本研究首次将云纹干涉法应用于复合材料单销钉连接件位移场的测量。从位移的云纹图用位移导数法求得销钉孔中心水平截面上的应变。根据复合材料层合板的直法线假设和层合板的折算刚度矩阵算出截面的平均应力分布。通过静力平衡,所得误差在6%以内。本研究结果证实,云纹干涉法测量复合材料连接件的应变场和应力场是有效的实验方法。      

高强度钢内螺纹冷挤压强化研究

研究了高强度钢内螺纹坟强化对疲劳性能的影响。利用高粘度云纹干涉法和扫描电镜,分别对螺纹牙根残余应力疲劳试件断口进行了测试和研究。疲劳对比试验结果表明,在应力为５００和６００ＭＰａ的条件下,经挤压强化的３００Ｍ高强度钢内螺纹的寿命是切削螺纹的４￣３０倍。     

内螺纹冷挤压强化对高强度钢疲劳性能的影响

研究了高强度人螺纹挤压强化对疲劳性能的影响。利用高精度云纹干涉法和扫描电镜,分别对螺纹牙根残余应力和疲劳试件口进行了测试和观察。疲劳对比试验结果表明,在应力为５００和６００ＭＰａ的条件下,经挤压强化的３００Ｍ高强度钢内方的寿命是切削螺纹的４～３０倍。     

铝合金对接焊缝几何云纹干涉测量法和数字相关方法应变测试研究

从计算机图像处理技术中的数字相关方法出发，结合几何云纹干涉的测试方法与实际工程背景，通过对铝合金对接焊缝拉伸几何云纹干涉试件进行力学性能试验，测定铝合金材料对接焊缝的力学性能，得到了理想的结果，为大应变的高精度、非接触、全场测量提供了一种良好的方法。     

承弯钢砼结构细观界面应变实验研究

本文采用云纹干涉法及其载波技术，对圆筋和人字纹筋两种钢砼结构试件承受弯曲载荷的不同材料界面应变进行实验分析，测取和确定了钢筋与混凝土的界面应变分布，结果表明：钢砼结构，由于配料成分性能的差异，其内部的应力应变状态极为复杂，沙石骨料水泥材料，及其与钢筋之间，不仅存在的挤压的正应变，而且存在较大的剪应变，钢筋与混凝土的界面区域，存在明显的挤压带和剪切带，这对于从细观上分析钢砼结构的应力，应变状态，认识     

抽样莫尔在材料变形分析中的应用

本文利用抽样莫尔法,对材料变形进行了精密测量.将罗琦光栅紧贴在试件表面,使其和试件材料一起变形,然后用CCD 摄像机获取在不同拉伸状态下的离焦变形条纹图.取出其中一幅变形条纹图,采用抽样和双线性插值等操作获取该状态下的多帧相移莫尔图,通过相移法计算莫尔相位,经相应公式的计算,得到材料的位移和应变分布.文中给出了抽样莫尔法基本原理,推导了位移应变计算公式并给出了实验结果.实验结果表明,由于抽样莫尔法只需一幅变形条纹图并结合相移技术获取材料的位移和应变等数据,因而能以较快速度和较高精度实时完成不同变形状态下材料的位移和应变等重要特性的分析.本文为动态过程中材料的变形提供了一种精密测量的方法.     

工程应力—应变曲线绘制的探讨

金属材料在受到轴向外力的作用下将产生变形,不断地施加外力,材料将由弹性变形、弹塑性变形到塑性变形,直至断裂。如果用一定放大比的仪器在拉伸或压缩过程中将变形放大绘制于记录纸上,便可得出拉伸或压缩曲线图。此图反映了材料受力后力与变形的全过程,是工程设计和使用至关重要的原始资料。由于生产上使用的零部件与试件的截面和形态不同,为便于设计计算,通常将拉伸曲线用计算方法重新绘制成工作应力-应变曲线编入材料手册提供使用。为此,如何精确和快速绘制应力-应变曲线就显得格外重要。 由于材质不同,材料有脆性与韧性之分,脆性材料的断裂往往发生在弹性范围内,即未及塑性变形试件就破     

用贴片云纹干涉法研究复合材料单孔连接件的应力场

本文采用贴片云纹法测定复合材料单孔连接件的应力分布,对四种不同复合材料制作的试件分别得到0°、45°、90°三个方向的平行云纹图,分析了通过孔心的水平横截面、孔侧的纵截面和孔受压处的纵对称截面上的应变和应力分布,并确定了不同复合材料的应力集中系数。      

用贴片云纹干涉法研究复合材料单孔连接件的应力场

本文采用贴片云纹法测定复合材料单孔连接件的应力分布,对四种不同复合材料制作的试件分别得到0°、45°、90°三个方向的平行云纹图,分析了通过孔心的水平横截面、孔侧的纵截面和孔受压处的纵对称截面上的应变和应力分布,并确定了不同复合材料的应力集中系数。     

智能材料结构损伤的分形神经网络诊断方法

针对智能复合材料的损伤诊断问题提出了采用人工神经网络将材料结构表面上的裂纹与材料内部的应力变化相结合的诊断方法。光纤珐珀传感器的小体积和高精度使之很适合于埋置在复合材料内部感受材料内部应力变化。而材料结构表面的裂纹是其内部受损伤的外在表现 ,根据裂纹在结构表面上的分布特征用分形的方法把表面的裂纹量化 ,获得其分维值 ,和内部的应力变化一起作为特征值输入到神经网络 ,利用神经网络的非线性处理能力进行在线的材料损伤识别。在一块 3 5cm× 3 5cm的复合材料试件上的实验结果表明这一方法是可靠的、有效的 ,完全可以进行材料损伤的在线监测以及进一步的材料寿命预测     

带圆孔玻璃/聚脂层板的疲劳损伤扩展

本文用云纹法研究了交变载荷作用下带圆孔玻璃纤维/聚脂层板的损伤扩展。云纹法能显示全埸位移应变分布,试件出现损伤时,能显示损伤区分布及裂纹扩展;由此得到柔度变化进而可以预测疲劳寿命。避免了在损伤分布不均匀时,因标距选取而影响灵敏度的问题。      

Instantaneous frequency and its application to strain extraction in moire interferometry

Moire interferometry is an effective experimental technique for measurement of in-plane deformation. However, it is information on the derivatives of the deformation, i.e., strains, that is usually desired in experimental mechanics. It is shown that the desired strains are the instantaneous frequencies of the fringe pattern and that either an energy operator or wavelet ridges can be used to extract the instantaneous frequencies from a single fringe pattern. The energy operator is a pixelwise processor; thus the strain extraction can be done on the fly, but it is sensitive to noise. The wavelet ridges extract the local features in the fringe pattern. The strain extraction is thus insensitive to noise, and good results are obtainable at the cost of longer computation time. The two methods can thus be chosen for different needs in strain analysis. The properties of the two methods as well as their applications to a real fringe pattern are given. The effectiveness of the proposed methods is illustrated by their comparison with traditional methods.     

Analysis of Shadow Moire Technique With Phase Shifting Using Generalisation of Carre Method

Abstract: Experimental stress analysis can be conveniently investigated by classical shadow Moire technique. Moire is a non‐contact and non‐destructive technique, with a fast digitisation process. The phenomena of Moire fringes are the result of the projection of the fringes of a ruling on a certain object. It has measurement accuracy comparable with other systems and also low cost. The present study offers new algorithms for phase evaluation in measurements. Several phase‐shifting algorithms with an arbitrary but constant phase‐shift between captured intensity signs are proposed. The algorithms are similarly derived as the so‐called ‘Carre algorithm’. The idea is to develop a generalisation of Carre algorithm that is not restricted to four images. Errors and random noise in the images cannot be eliminated, but the uncertainty caused by their effects can be reduced by increasing the number of observations. An experimental analysis of the mistakes of the technique was made, as well as a detailed analysis of mistakes of the measurement. The advantages of the proposed algorithm are its precision in the measures taken, speed of processing and the immunity to noise in signs and images.     

计量光栅信号质量综合评价系统

光电轴角编码器中的莫尔条纹信号质量决定了整个系统的细分精度。计量光栅信号质量综合评价系统由编码器、数据采集卡和相应的软件组成，采用一种以莫尔信号离散采集和数据处理为主的数字化检测方法，实现了莫尔条纹信号质量各项指标的评价，对提高测量精度以及光栅系统的设计具有一定意义。     

Research on identification of nonlinear damping based on time frequency analysis

Abstract

According to the relationship between damping, strain and time, the piecewise linear wavelet transform and the piecewise linear short time Fourier transform methods are put forward to identify the nonlinear damping of alloy material. The overall nonlinear property of damping is derived from the piecewise local linearisation. The satisfied results obtained from simulations demonstrate that the methods presented are effective. Usually, damping measured in the non-uniform stress field is only a volumetric average. To overcome this deficiency, a trapezoid specimen with quasi-uniform stress field is developed on the basis of the traditional damping experimental equipment. The damping measurement experiment is carried out. The measurement signal is analysed by the two methods presented. The relation curve of damping versus strain has shown that the damping capacity of the alloy Al–33Zn–6Si increases with the increasing strain. The relationship between damping and strain appears obviously nonlinear.     

Optical grating diffraction method: from strain microscope to strain gauge

The grating diffraction method for direct strain measurement is reviewed. Two systems which use this method are presented. The first system is a compact strain microscope. A Leitz optical transmitting microscope with white light source is reconstructed by developing a loading and recording system. Gratings with median density of between 40 and 200 lines/mm are used. With the help of a Bertrand lens, the Fourier spectrum of the grating is formed with high image quality on the CCD sensor plane. Software is developed to precisely, quickly and automatically determine the diffraction spot centroids. The second system is a new strain sensor based on a high-frequency grating and two Position Sensor Detectors (PSDs). The grating, attached to the surface of the specimen, is illuminated by a focused laser beam, generally with a frequency of 1,200 lines/mm. The centroids of diffracted beam spots from the grating are automatically determined using two PSD sensors connected to a personal computer. The shift of diffracted beam spots due to specimen deformation is detected. Strain sensitivity of one micro-strain can be obtained, as can a 0.4 mm spatial resolution for strain measurement. The system can be used for both static and dynamic tests.     

Effects of the environmental conditions on the mechanical behaviour of the corrugated cardboard

Corrugated cardboard is very sensitive to atmospheric conditions. The aim of this work is to study the effects of these parameters, in fact the relative humidity (RH), on the mechanical behaviour of a sandwich structure of the corrugated cardboard type. For that, tensile tests were used under various rates of relative humidity. In high rates of moisture, the instrumentation must be adapted. A preliminary comparison of several measurement methods of the mechanical properties was carried out. It made it possible to validate the method of strain measurement using the measurement of the displacement which requires a minimal handling of the specimen. During this study, the effect of the water content on the mechanical properties is presented. Moreover, the viscoelastic character coupled with the damage of this material is high lighted.     

A technique for dynamic tensile testing of metals

A technique is described for obtaining full dynamic stress/strain curves in tension up to strain rates of 100^s-1. In conjunction with a high speed servo-hydraulic machine, a low inertia extensometer has been developed to facilitate measurement of specimen tensile strain up to fracture.
The benefits of the technique are highlighted in relation to currently available methods for dynamic stress/strain measurement.     

A general linear method to evaluate the hardening behaviour of metals at large strain with full‐field measurements

The hardening behaviour of metals is generally described in terms of a stress‐strain curve derived from experiments. In this paper, a linear method to identify the stress‐strain curve starting from full‐field measurement data is presented. This method can be applied to any stress state using a generic yield function, the only requirement is that the full‐field measurement is extended up to the border of the specimen. The method is presented and validated using a finite element model of a notched specimen. Moreover, experiments were performed on specimens cut from a BH340 steel sheet to illustrate the viability to actual cases. Two geometries were considered, a standard uniaxial test, where the method was used to evaluate the post‐necking behaviour, and a notched specimen with a heterogeneous strain field. The proposed method, named linear stress‐strain curve identification (LSSCI), can be a useful tool in combination with inverse methods to identify the constitutive behaviour of metals in large strain plasticity.