Recent Developments of Material Deformation Measurement

Material deformation measurements are divided into two main classes: contact type measurement and non-contact type measurement. The principles of strain gauge contact type extensometers in small range and large range measurement, non-contact video and non-contact laser extensometers are described, respectively. Furthermore, advantages and disadvantages of these extensometers are reviewed. The contact type extensometers provide a high level of measurement accuracy, but the knife edge is easily damaged during the fracture of high stiffness materials; the total deformation process is not measured unless knife edge is not unloaded post-fracture; meanwhile, the reversal phenomenon is accompanied in tensile test. Accordingly, the resolution of the reversal phenomenon is discussed; Non-contact video extensometers may be used up to the material breaking point without damage, even when testing specimens that exhibit whiplash, but marks on specimens deform following specimens deformation in tensile test, and marks are not automatically and accurately tracked; Although, non-contact laser extensometers provide a higher level of measurement accuracy and wide range of application, it is expensive. On the basis of these discussions, a novel materials deformation measurement method based on laser mark automatic tracking is presented. This method has advantages of simple, high accuracy and wide range of application.