Research On Video-extensometer System

The deformation amount caused by external loads is extremely important parameter of material mechanical properties in the field of research, and electronic extensometer plays a key role in the measurement of material deformation at present. However, its poor adaptability by different versions of extensometer matching different specifications of sample limits its range of application. Video-extensometer is the contactless strain measuring equipment, so the development of this product has some engineering values as is researched in this paper because of its advantages such as the freely determination of the range of measurement, not easily damaged, and excellent adaptability and so on.Based on the existing theoretical research and application on the video extensometer, I take into account two major principles in this paper. Firstly, it needs to satisfy the great accuracy and high efficiency in the real-time measurement. Secondly, it should save the cost. Given the fist aspect, proper measuring technology of image, edge detection technology, and camera calibration technology is proposed. In light of the other, appropriate experiment equipment is not only selected which include CCD camera, industrial optics and LED light, but also the type of the hardware and the scheme of hardware analyzed. Given the theory above, I develop a software integrated by measurement and control on the basis of the platform of VC6.0. This platform following three steps realizes its functions. Firstly, it gathers images at the rate of the millisecond time by controlling the CCD camera, on the other hand, it realizes the camera calibration and dynamic measurement for the elongations of tensile specimens by the image processing algorithm in this paper. Then, the range of sampling frequency, the measurement's span, and the level accuracy of the Video-extensometer studied in this paper is calculated by experiment. In the last, an experiment compared with the electronic extensometer for the amount of stretch of 45# steel is conducted. The result shows that this study can achieve high accuracy. It is worth mentioning that the elastic modulus of 45# steel is calculated according to the result above within the actual range.