应用自动网格法测量带孔洞大样品的变形

为了能在现场检测带孔洞大样品的变形,本文提出了运用环形编码法的改进自动网格法。文中还研究了适用于大样品测量的网格制作技术,编制了网格自动处理及分析软件,进行了计算机模拟和实验标定,并分析了测试精度。     

一种新的准结构网格生成方法

在有限元分析中，高质量的结构网格可以有效地提高有限元分析的精度，但结构网格的几何适应性差，针对复杂边界的二维计算模型，现有的方法很难自动生成高质量的结构网格；而非结构网格几何适应性很好，但存在计算效率低和精度差等问题。提出了一种新的准结构网格生成方法，能够实现复杂区域的网格自动生成并且具有高网格质量。该方法首先对计算区域运用Delaunay三角剖分技术生成粗背景网格；然后利用背景网格，使用优化的Voronoi图生成过渡的蜂巢网格；最后，通过中心圆方法对蜂巢网格单元进行结构网格剖分。分析NACA0012翼型数值模拟结果表明，提出的新准结构网格生成方法能够对边界复杂的模型自动生成高质量的网格，并且通过三种不同拓扑类型网格计算结果相互对比及与实验结果对比，证明准结构网格具有高计算精度。     

平面区域四边形网格自动生成技术

本文分析和综述了四边形网格自动生成的各种算法，给出了三角形网格向四边形网格转换的局部算法，以及有ＦＧＴ思想直接生成四边形和三角形网格算法。详细分析了此法之下生成网格的几何拓朴性质，最后给出实例验证了算法的有效性。     

板壳畸变单元的无网格和有限元自动耦合方法

板壳大变形时单元的严重畸变会使计算精度降低。无网格局部Petrov-Galerkin法是一种真正的无网格方法,能够消除网格畸变,但比有限元法计算效率低。根据板壳网格畸变的局部性特点,利用过渡单元法,基于板壳网格质量,建立了板壳的网格严重畸变区域由有限元分析切换为无网格分析的自动耦合算法,实现了有限元法和无网格局部彼得罗夫．迦辽金法的耦合。应用实例表明：通过自适应耦合,既能发挥有限元法计算效率高的特点,又能发挥无网格法适合大变形分析、没有网格畸变造成计算困难的特点。     

双频自动网格法研究

传统的自动网格法常采用均匀布点法，这对应变集中区域的变形测量极为不利。节点过多，检测精度会下降，节点少了，会降低应变集中区域的空间分辨率。本文提出了双频自动网格法，在应变集中区域增加节点。文中研究了双频网格点的制作技术及对双频网格图的自动处理与分析。并应用双频自动网格法测量了中心带孔铝试件在拉伸加载过程中的孔边位移场。     

一种全四边形网格生成方法——改进模板法

首先对全四边形单元网格自动剖分算法中的模板法进行了探讨，并提出了相应的改进方法。在此基础上提出了一种新的全四边形单元网格自动生成方法。该方法允许在两个方向上存在网格疏密过渡，并可以提高单元的密度要求自动计算亲单元每条边上的结点数，有效地对局部实施加密处理。     

多特征几何体的全六面体网格自动生成方法

有限元分析的精度和效率与网格划分的质量有直接关系.目前尚缺乏一种普适性的自动网格划分方法,尤其是对于具有多种几何特征的复杂模型,现有的六面体网格自动划分算法存在不同几何特征间的网格兼容性较差以及孔状特征周围网格质量不高的问题.对此本文提出一种基于映射法的六面体网格自动生成方法,在映射法的基本框架下,将物理空间中的复杂几何体映射为计算空间中的规则几何体,引入边界顶点分类,将复杂几何体边界进行简化,将子域约束进行连接,寻找贯穿边界,以使映射网格在约束特征间兼容;对圆弧特征进行等效转化,降低曲率过大对于网格过渡的影响.实例验证表明,本方法稳定可靠,生成的六面体网格质量较高,能够解决多特征复杂几何体六面体网格自动划分问题.     

一种新的准结构网格生成方法

在有限元分析中,高质量的结构网格可以有效地提高有限元分析的精度,但结构网格的几何适应性差,针对复杂边界的二维计算模型,现有的方法很难自动生成高质量的结构网格;而非结构网格几何适应性很好,但存在计算效率低和精度差等问题。提出了一种新的准结构网格生成方法,能够实现复杂区域的网格自动生成并且具有高网格质量。该方法首先对计算区域运用Delaunay三角剖分技术生成粗背景网格;然后利用背景网格,使用优化的Voronoi图生成过渡的蜂巢网格;最后,通过中心圆方法对蜂巢网格单元进行结构网格剖分。分析NACA0012翼型数值模拟结果表明,提出的新准结构网格生成方法能够对边界复杂的模型自动生成高质量的网格,并且通过三种不同拓扑类型网格计算结果相互对比及与实验结果对比,证明准结构网格具有高计算精度。     

复杂区域非结构化四边形网格全自动生成方法

针对多介质平面复杂区域，本文建议了一种基于推进网阵法的全四边形网格自动生成方法，其特点是对不规则区则区域适应能力强，考虑了节理单元自动生成。文中提出了网格质量改进方法，并给出了三个工程算例。     

复杂区域非结构化四边形网格全自动生成方法

针对多介质平面复杂区域，本文建议了一种基子推进网阵法的全四边形网格自动生成方法。其特点是对不规则区域适应能力强，考虑了节理单元自动生成。文中提出了网格质量改进方法，并给出了三个工程算例。     

软材料接触力学问题的实验研究

针对硫化硅橡胶在刚性压头作用下的大变形接触问题,研究了橡胶类软材料接触区区域变形场的实验测量技术。为了研究硫化硅橡胶与刚性体在试件内部接触的大变形问题,本文提出了一种体内数字栅云纹实验技术,给出了该技术的原理和实现方法。然后运用数字图像处理方法得到了橡胶材料大变形位移u场、v场,并结合橡胶材料在压头作用下的理论分区模型,分析了软材料接触区域的大变形场,讨论了接触区域的变形分区规律,并初步给出了接触区域应变计算方法。     

Automated fringe pattern analysis for moiré interferometry

The theory of an automated fringe-pattern analysis using temporal phase stepping method for moiré interferometry is presented. The automated method provides a fast and accurate strain measurement for moiré interferometry. Measurements on a tapered composite specimen with a dropped ply are shown to highlight the capability of this technique to obtain the strain distribution, particularly around the region with a dropped ply.     

Computer aided photoelasticity by an optimum phase stepping method

In this paper an automated photoelastic method based on the phase stepping technique is described. It provides full-field maps of the isoclinic parameter and the relative retardation. The technique is based on processing six images of a photoelastic specimen acquired using plane and circularly polarized light. The number of acquisitions and the type of polariscope used in this approach have been chosen with the aim at reducing the influence of quarter wave plate errors and obtaining raw photoelastic data in a periodic form suitable for easy applications of automatic unwrapping routines.     

一种快速稳健的并行多块结构动网格方法

为解决传统网格处理方法不能满足复杂外形在大设计空间内进行优化时对网格质量的要求的问题,提出了一种并行多块动网格方法,该方法基于初始外形的多块结构网格,根据优化过程中个体外形与初始外形拓扑结构相近的特性,利用体样条插值方法来拟合多块结构网格各块顶点的位移,得到几何外形变化后的拓扑结构,再利用无限插值方法并行地移动初始外形多块结构网格的边、面和块内的网格点,进行光顺处理后得到变形后几何外形的空间网格;该方法在保证网格质量的同时,可以极大地提高网格生成效率,本文以某翼身组合体为例结果表明,该方法在大设计空间的复杂外形设计问题中具有很强的实用性。     

A practical multiplied-moiré system

This paper describes a multiplied-moiré-fringe system, of in-plane displacement measurement, which is particularly suitable for high-sensitivity studies, both under laboratory conditions and for field studies. A replica technique is used for applying a relief grid to the specimen, and for recording the deformed grid. A fringe-multiplication method is used to give effective line densities in the range 400–2,000 lines/mm (10,000–50,000 lines/in.). Application of the method to fatigue studies is described.     

An algorithm of finite element grid generation for three-dimensional complex connected domain

An automated quasi three-dimensional finite element grid generation method is presented for particular three-dimensional complex connected domain, across which some are simply connected two-dimensional.regions and some are multiply connected two-dimensional regions. A subdivision algorithm based on the variational principle has been developed to ascertain the smoothness and orthogonality of the generated grid in any cross sections. Smooth transition between the simply and multiply connected regions is maintained. For illustration, the method is applied to generate a finite element three-dimensional grid for human above knee stump.     

Grid Method for Microscale Discontinuous Deformation Measurement

The objective of this paper is to explore both grid method and Digital Image Correlation (DIC) technique for microscale and discontinuous displacement measurements, such as those associated with crack tips. First, the principle of the grid method is revisited. The grid method and DIC technique are then applied to computer generated images to calculate the displacement field around crack tips. Finally, the grid method is applied to actual experimental images of fracture tests which are conducted inside a Scanning Electron Microscope (SEM) chamber. A new technique is developed to generate microscale pattern that is suitable for both grid method and DIC technique. The displacement fields calculated from grid method are compared with those from DIC technique to identify the strengths and weaknesses of each technique for the microscale and discontinuous displacement measurements. It has been determined that grid method can obtain data closer to the discontinuity than DIC; however, DIC produces smoother displacement fields at the far field. Using this new pattern generation technique, both grid method and DIC technique can be applied to the fracture test at the microscale to complement with each other to achieve the best experiment results.     

Stress and strain distributions beyond general yield in the Charpy V-notched specimen

The visioplasticity method has been used to obtain the stress and strain distributions during planestrain bending in a standard Charpy V-notched specimen of low carbon steel. The specimen was slit longitudinally through the notch with a square grid inscribed on the interface. The instantaneous grid distortion was obtained during a three-point incremental bending test. A computer program was developed for the calculation of the instantaneous stress and strain distributions using the experimentally determined displacement field and the true stress-strain curve of the steel.     

Optical measurement of the specimen deformation at high strain rate

During recent years, the investigation of the strain-rate-dependent properties of materials has become more and more important. The experimental techniques used to establish the specific dynamic behavior of materials all have in common that the acquisition of information concerning the deformation of the specimen is cumbersone and often questionable. Mostly, only limited information on the spatial distribution and time evolution of the deformation in specimen can be obtained. In this paper, a non-contact, optical technique is presented, providing the time evolution and spatial distribution of the axial deformation in specimens during a high strain rate test. The deformation of a line grid attached to the specimen is recorded during an experiment by means of a rotating drum camera. The time history of the axial displacements is subsequently derived by an advanced technique based on digital geometric moiré combined with a phase-shift method, specially developed to this purpose. The technique can be applied to a wide range of materials and high strain rate tests, and is illustrated by means of a split Hopkinson tensile bar experiment on a steel sheet specimen.