An Evaluation of Digital Image Correlation Criteria for Strain Mapping Applications

Abstract:  The performance of four digital image correlation criteria widely used in strain mapping applications has been critically examined using three sets of digital images with various whole-field deformation characteristics. The deformed images in these image sets are digitally modified to simulate the less-than-ideal image acquisition conditions in an actual experiment, such as variable brightness, contrast, uneven local lighting and blurring. The relative robustness, computational cost and reliability of each criterion are assessed for precision strain mapping applications. Recommendations are given for selecting a proper image correlation criterion to efficiently extract reliable deformation data from a given set of digital images.     

复杂变形中单一应变因素的测量

以薄壁管受力变形为例，介绍了一种对扭转引起的应变的测量方法。     

基于DSP的光纤法珀应变仪数据采集技术研究

针对基于TMS320VC33的DSP光纤法珀应变测量仪，对VC33与光电转换模块之间的数据采集进行了探讨，重点介绍了VC33与光电转换模块的命令发送和数据采集的思路及软件实现，在此基础上，得到的光纤法珀应变传感器干涉信号图与理论上传感器的干涉信号图分布基本一致，并对产生差异的原因做了简单说明。验证了该采集技术的可行性。     

模态试验在梁损伤诊断中的应用研究

针对位移模态参数对结构损伤欠敏感，应用应变模态试验技术诊断结构损伤位置和程度。根据模型梁试验，重点比较研究损伤对位移模态、应变模态影响规律及其灵敏程度。得出应变模态对非节点损伤非常敏感，在损伤处附近发生突变，应变值分布也有较明显改变，尤其是跨中损伤第一阶、四分之一跨损伤第三和第二阶。     

控制厚度分布的正反向超塑胀形的有限元分析

为研究正反向超塑胀形工艺对厚度分布的影响,应用商业有限元软件MARC对带有凹槽的深盒形7475合金零件正反向超塑胀形过程进行了有限元模拟,并对不同工艺条件下成形后零件的壁厚分布结果进行了分析.研究表明:正反向超塑胀形工艺是控制成形零件壁厚的有效途径,通过优化压力-时间曲线和反向胀形模具形状,明显改善了零件的厚度分布,达到了零件的设计要求;后处理直观地显示了该零件正反向超塑胀形的全过程,为成形提供了合理的方案;零件变形各阶段的应变速率控制在7475合金的应变速率范围内,证明压力-时间曲线设计合理.     

Werkstoffkennwerte für die Lebensdauerberechnung von Strukturen aus Stahlfeinblechen für den Automobilbau

Materials Data for Fatigue Life Calculation of Steel Sheet Structures for Automotive Engineering Within a joint project of the steel and automotive industry 17 steel sheet materials for automotive engineering in various delivery and forming conditions at temperatures of –40 °C, 22 °C and 100 °C were investigated. In the course of 37 test series strain controlled fatigue curves to crack initiation and stress‐strain‐curves under monotonic and cyclic loading were determined. All experimental data, hysteresis loops and determined cyclic properties are available in a database. A correlation between the mechanical properties from tensile tests and the properties from strain controlled cyclic experiments seems to be possible.     

An improvement of the EDI method in linear elastic fracture mechanics by means of an a posteriori error estimator in G

In this paper, an error estimator that quantifies the effect of the finite element discretization error on the computation of the stress intensity factor in linear elastic fracture mechanics is presented. In order to obtain the proposed estimator, a shape design sensitivity analysis (SDSA) is applied to the fracture mechanics problem. Following this approach, one of the most efficient post‐processing techniques for computing the strain energy release rate G, the well‐known EDI method, may be interpreted as a continuum method of the SDSA. The proposed error estimator is based on the recovery of the gradient fields and its reliability has been checked by means of numerical problems, yielding very good estimations of the true error. The new estimator remarkably improves the results given by a previous error estimator, which is based on a discrete analytical approach of SDSA. As a consequence, the combination of the new error estimator and the result given by the EDI method provides a much more accurate estimation of G. Copyright © 2003 John Wiley & Sons, Ltd.     

Algorithms for the analysis of 3D finite strain contact problems

From the constraint imposition aspects in 3D to friction regularization, various ideas are exposed in this paper. A variation of the Rockafellar Lagrangian is proposed which results in continuous second‐order derivatives if Lagrange multiplier estimates are greater or equal than one. This fact allows the adoption of a full second‐order (i.e. Lagrange–Newton) method avoiding sequential unconstrained minimization techniques. An algorithm for global and local contact detection is presented which is developed for dealing with large step sizes typical of implicit methods. A modified constraint definition to deal with non‐smooth situations is presented. Aspects of friction implementation, including a regularization scheme which ensures stepwise objectivity, are detailed. Finally, several illustrative examples are carried out with success. Copyright © 2004 John Wiley & Sons, Ltd.