Analysis of necking behavior in ultrafine-grained material by optical strain measurement

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Necking behavior in tensile test of ultrafine grained aluminum was analyzed by full-field optical strain measurement method. Fracture strain was larger than 30% in the aluminum whose mean grain size was larger than 1.7μm. In the specimens, most of the gage region of tensile specimen was deformed when necking started. The necking region became narrower with increasing the tensile strain. The specimen having mean grain size of 0.24μm showed fracture strain of 9%. The necking region of the specimen with grain size of 0.24μm was narrower than that of the specimens whose mean grain size was larger than 1.7μm.