Direct Evaluation of Strain and Strain Distribution Using Grid Method during Shear Deformation of Metal Matrix Composites

A grid method is applied to measure the specimen's strain during dynamic deformation in the split-Hopkinson torsional bar(SHTB) experiments. A streak camera is used to record the motion of an inclined grid pattern(5 lines/mm)previously formed on the outer surface of the specimen. The average shear strain of the metal matrix composites(MMC) is successfully obtained in a large strain range by analyzing frequency of the streak image. The nominal shear strain evaluated by the conventional SHTB method agrees well with the directly measured strain for these materials. Microscopic strain distribution in MMC is also measured by observing a diffraction grating(600 lines/mm)on the specimen's surface in quasi-static testings. Localization of the shear strain becomes strong with increasing volume fraction of the reinforcement, and would reduce ductility of the composite materials.