A semi-automatic measurement system based on digital image analysis for the application to the single fiber fragmentation test
A semi-automatic measurement system based on digital image analysis for the application to the single fiber fragmentation test
复制标题
基于数字图像分析的半自动测量系统应用于单纤维断裂测试
DOI：
10.1117/12.2020268
复制
发表时间：
2013
期刊：
影响因子：
--
通讯作者：
V. Ulbricht
中科院分区：
文献类型：
--
作者：
S. Blobel;K. Thielsch;V. Ulbricht
纤维增强复合材料的有效宏观材料行为的计算预测是开发这些材料的潜力的研究目标。除了材料组件的机械特性之外，还需要对这些组件之间的机械相互作用有广泛的了解，以便建立局部材料结构的合适模型。例如，对简化的复合材料试样的微观力学损伤行为的实验研究可以帮助理解导致纤维断裂附近的基体和界面损伤的机制。为了实现一个合适的实验装置，一种新的半自动测量系统的基础上，利用光弹性和图像相关的数字图像分析。应用于具有双折射基体材料的试件，它能够同时提供损伤演化和应力应变状态的全局和局部信息。图像采集是使用长距离显微镜光学实现的，有效分辨率为每像素2微米。当系统沿着试样的感兴趣区域移动时，所获取的图像被在线组装并用于结合载荷框架提供的全局力-位移曲线来解释光学提取的信息。用圆偏振光照射样品，并通过偏振器和四分之一波片的不同配置投射透射光，使得能够在四百万像素的图像传感器的象限处同步捕获四个图像。将第五图像从同一光路解耦并投影到第二相机芯片，以同时获得同一场景的非偏振图像。这种光学设置的好处是有机会在本地提取广泛的信息，而不会影响实验的进展。这四幅图像用于获得基于光弹性的应力分布信息，而第五幅图像提供局部应变作为图像相关算法的结果，并能够观察和记录可见的损伤现象。一次采集五个不同的图像允许应用于具有随时间变化的机械行为的材料，这是所开发的测量光学器件的重要附加值。实验装置被施加到所谓的单纤维断裂试验，它定义了一个共同的测试程序来研究透明基体材料中的单根长纤维增强试样的损伤现象。当在低应变率下向试样施加拉伸载荷时，纤维的损伤出现，而基体材料没有完全失效。作为纤维局部失效的结果，可以观察到载荷传递到周围的基体材料和特征应力分布的出现以及逐渐形成的基体和界面裂纹。使用所描述的测量系统，可以估计断裂纤维附近的基质材料的应力和应变分布。结合损伤现象的记录和分类，这使得能够解释复合材料内部的应力重分布过程。这些知识可以用来分析细观力学现象和有效宏观材料行为之间的相关性，以及识别界面破坏本构模型的参数。文章展示了测量系统的潜力，并介绍了其应用于单...
The computational prediction of the effective macroscopic material behavior of fiber reinforced composites is a goal of research to exploit the potential of these materials. Besides the mechanical characteristics of the material components, an extensive knowledge of the mechanical interaction between these components is necessary in order to set-up suitable models of the local material structure. For example, an experimental investigation of the micromechanical damage behavior of simplified composite specimens can help to understand the mechanisms, which causes matrix and interface damage in the vicinity of a fiber fracture. To realize an appropriate experimental setup, a novel semi-automatic measurement system based on the analysis of digital images using photoelasticity and image correlation was developed. Applied to specimens with a birefringent matrix material, it is able to provide global and local information of the damage evolution and the stress and strain state at the same time. The image acquisition is accomplished using a long distance microscopic optic with an effective resolution of two micrometer per pixel. While the system is moved along the domain of interest of the specimen, the acquired images are assembled online and used to interpret optically extracted information in combination with global force-displacement curves provided by the load frame. The illumination of the specimen with circularly polarized light and the projection of the transmitted light through different configurations of polarizer and quarterwave-plates enables the synchronous capturing of four images at the quadrants of a four megapixel image sensor. The fifth image is decoupled from the same optical path and is projected to a second camera chip, to get a non-polarized image of the same scene at the same time. The benefit of this optical setup is the opportunity to extract a wide range of information locally, without influence on the progress of the experiment. The four images are used to obtain information on the stress distribution based on photoelasticity, while the fifth image delivers the local strain as outcome of an image correlation algorithm and enables the observation and documentation of the visible damage phenomena. The acquisition of five different images at a time allows for the application to materials with time-dependent mechanical behavior which is an important added value of the developed measurement optics. The experimental setup is applied to the so-called single fiber fragmentation test, which defines a common test procedure to study the damage phenomena of single long-fiber reinforced specimens in transparent matrix material. When a tension load is applied to the specimen at low strain rate, damage of the fiber arises without a complete failure of the matrix material. As a result of the local failure of the fiber, a load transfer to the surrounding matrix material and the appearance of a characteristic stress distribution as well as evolving matrix and interface cracks can be observed. Using the described measurement system, it is possible to estimate the stress and strain distribution of the matrix material in the vicinity of the fractured fiber. In combination with the documentation and classification of the damage phenomena this enables the interpretation of the stress redistribution process inside the composite. This knowledge can be used to analyze the correlation between micromechanical phenomena and the effective macroscopic material behavior as well as to identify parameters of constitutive models for interface failure. The article demonstrates the potential of the measurement system and presents the results of its application to the single …