13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- grain family, very little residual elastic lattice strain (<150×10-6 strain) was accumulated during incremental tensile deformation of specimens subjected to prior deformation at high temperature. {200} grain family Deviation from linearity, ε∗106 -600 -400 -200 0 200 400 600 800 Applied true stress, MPa 0 50 100 150 200 250 300 350 400 450 Specimen 1 Specimen 2 Specimen 3 Specimen 4 {220} grain family Deviation from linearity, ε∗106 -600 -400 -200 0 200 400 600 800 Applied true stress, MPa 0 50 100 150 200 250 300 350 400 450 Specimen 1 Specimen 2 Specimen 3 Specimen 4 (a) (b) Figure 4. Influence of prior deformation at high temperature on the subsequent elastic lattice strain response: (a) {200} grain family; (b) {220} grain family. {200} grain family Plastic strain after unloading (RT), % 0.001 0.01 0.1 1 Elastic lattice strain after unloading, 106 -500 -400 -300 -200 -100 0 100 200 300 400 Specimen 1 Specimen 2 Specimen 3 Specimen 4 {220} grain family Plastic strain after unloading (RT), % 0.001 0.01 0.1 1 Elastic lattice strain after unloading, 106 -500 -400 -300 -200 -100 0 100 200 300 400 Specimen 1 Specimen 2 Specimen 3 Specimen 4 (a) (b) Figure 5. ND measured elastic lattice strain after each step of unloading, measured at a stress of 5MPa, plotted against the accumulated plastic strain at room temperature: (a) {200} grain family; (b) {220} grain family 3.2. Internal stress Figs. 6 (a) and (b) show the internal stresses along the axial and radial directions for specimens subjected to prior deformation. In general, an increase in the magnitude of the prior strain led to a higher internal stress. In addition, the internal stress was shown to have a crystallographic orientation dependence: internal stress in {200} grain family was tensile, whereas the other three were compressive. Of the three grain families the {220} grain family contained the highest compressive internal stress. Rietveld refinement predicted an averaged value for four grain families considered in Figs. 6 (a) and (b). It is interesting to note that {200} grain family in specimen 4 (highest total true axial strain) had a very similar value of internal stress compared with specimen 3. However, the {220} grain family in specimen 4 had an increased value of internal stress compared with specimen 3. These two phenomena are consistent with the in-situ observations shown in Fig. 4 (a) and (b), where a very similar lattice strain response was observed in the {200} grain family from specimens 3 and 4; this is different for the {220} grain family.
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