Metals exhibit inhomogeneous deformation features under plastic strain, leading to the appearance and evolution of the deformation bands. The quantitative characterization of this effect is significant for an in-depth understanding of the plastic deformation and strengthening mechanisms of metals. In this work, the full-field strain information are obtained using digital image correlation method, and the work hardening behaviour in Ni single crystals is investigated from the angle of strain heterogeneity. First, a digital image correlation method, adapted for characterizing single crystal deformation, is proposed for the precise evaluation of strain field. The tensile test results show that the plastic strain in Ni single crystal manifests a distinct localization characteristic, which is closely linked to the slip band formation and development process. Based on the characteristics of the strain field evolution, 3 deformation regimes can be determined, which demonstrate a one-to-one correspondence to the 3 work hardening stages of the material. Some reasonable interpretations of their correlation are proposed within the framework of dislocation theories, which are verified through the experimental observations on the microstructure evolution of the material.
Fund: Supported by National Natural Science Foundation of China (No.11172096) and Foundation for the Author of National Excellent Doctoral Dissertation of Higher Education from the Ministry of Education of China (No.201235)
Fig.1 Schematic of geometric dimensions of the specimen (unit: mm)
Fig.2 Surface morphology of the specimen after deformation obtained by digital camera
Fig.3 Axial (a) and transverse (b) displacement fields in the final deformation state
Fig.4 Axial stress-strain curve and equivalent von Mises strain fields (insets) for the labeled points
Fig.5 Representative equivalent von Mises strain (eeq) fields for the deformation regimes I (a), Ⅱ (b) and ⅡI (c)
Fig.6 Distribution of εeq by band under the deformation regimes I, Ⅱ and ⅡI
Fig.7 Evolution of sensitive index (sB) during the tensile test and determination of the 3 deformation regimes
Fig.8 Shear stress-strain (t-g) and work hardening rate-strain (q-g) curves and work hardening stages
Fig.9 Dislocation densities under different strain levels (rw—density of dislocation walls, rc—density of dislocation cells, rt—overall dislocation density of material)
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