Development of a simple automatic measurement of the deformation or strain using a TV camera

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This study is the development of an automatic measurement, taken by TV camera, of the deformation of real objects. The images from a TV camera or a microscope are digitized and stored in the computer memory while the specimen is being deformed. The images recorded at different times are compared each other and the deformation is calculated automatically. Fortunately, since the magnified surface image has a characteristic pattern, it can be utilized for the adequate marking and, therefore, the manual drawing of meshes or marks on the surface is unnecessary. The cross-correlation method is used for the image processing. In the cross-correlation method, the first original image is divided into small square meshes on the computer memory. Though the size of meshes should be changed depending on the magnification of a microscope or the grain size of a specimen, in this technique the size can be changed easily without contact to the surface since the image data is processed on the computer memory.In our experiments, static tensile and torsional tests of carbon steels are carried out. Then those specimen surfaces are locally observed. The characteristic of micro-deformations under these static loads is made clear from the results obtained by the image processing technique.