材料力学性能显微测试系统

介绍了适用于毫、微米量级材料的力学性能测试系统,该系统包括微型加力装置、显微镜及数字图像处理系统。通过计算机控制,加力机构可以对微小试件按力或位移控制方式加载,载荷大小通过传感器直接由计算机数字化。试件的变形测量采用数字图像相关技术,通过序列图像分析方式,获得试件在不同外力作用下对应的变形,从而获得该材料的应力应变关系。在利用显微镜对微细观图像进行放大时,图像的畸变会影响相关计算的精度,本文采用了精度极高的正交栅板,对成像系统进行标定,有效地消除了高放大倍数下的图像畸变。图像相关技术对被测物体的表面处理非常敏感,本文也对这一问题进行了讨论,并给出两个不同的应用实例。第一个为材料性能试验,对厚度为0.1mm的铝材进行单向拉伸,给出了材料的应力应变关系;第二个为稳态裂纹扩展试验,对用人牙制作的紧凑拉伸试件进行测试,获得裂尖后的COD曲线。实验表明,该测试系统在微细观力学实验中具有广阔的应用前景。

A Test System for Mechanical Behavior of Materials in Microscale

In this paper,a test system for mechanical Behavior of materials in meso and micro scales is described.It is comprised of a miniature loading frame,a microscope and an imaging system.The loading frame can work in either load-control or displacement-control mode,and signals from the load sensor are digitalized with the control computer.Sequential images are taken while specimens are stressed.Digital Image Correlation(DIC) is employed to analyze the corresponding strain in each load step.In order to improve the precision of strain analysis,lens aberration is considered at high magnification.A plane glass plate coated with precise cross grating is used as a benchmark to eliminate the error caused by microscope.Surface preparation is also discussed at microscale.Two examples are presented.One is the mechanical property of an Aluminum sheet with thickness of 0.1 mm tested under uniaxial tension.The other shows the COD curve behind the crack tip in a small dentin compact tension specimen after the whole displacement field is determined with DIC.Experimental results illustrate that DIC is a powerful tool in identifying the displacement/strain filed in micro scale.