13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- Axial Direction Total true axial strain accumulated at high temperature, % 0 1 2 3 4 5 6 7 8 Axial internal stress, MPa -250 -200 -150 -100 -50 0 50 100 150 200 {111} {200} {220} {311} Rietveld Analysis Radial Direction Total true axial strain accumulated at high temperature, % 0 1 2 3 4 5 6 7 8 Radial internal stress, MPa -250 -200 -150 -100 -50 0 50 100 150 200 {111} {200} {220} {311} Rietveld Analysis (a) (b) Figure 6. Internal stresses in specimens 1 to 4, which were subjected to a prior deformation at high temperature: (a) axial direction and (b) radial direction 3.3. Internal resistance Using the incremental tensile deformation for each specimen combined with neutron diffraction measurements, the magnitude of applied stress required to create room temperature plastic deformation was obtained. This is judged to be a measure of the internal resistance to material flow. Fig. 7 shows the internal resistance in the four specimens summarised in Table 2. Internal resistance obtained from the bulk stress-strain, {220} grain family is shown in Fig. 7. Here, the 0.01% plastic strain is used as a benchmark to determine the yield point for both macro-scale and grain family size-scale conditions. The internal resistance was determined using: 0.01%, ir bulk bulk a σ σ = (5) 0.01%,{220} 220 ir a σ σ = (6) 0.01% 220 220 220 ir E σ ε = × (7) Equation 5 provides a measure of the macro-scale internal resistance, ir bulk σ , and was determined from the applied stress required to introduce 0.01% macro-scale plastic strain. Equation 6 provides a measure of the grain family size-scale internal resistance, 220 irσ , determined from the applied stress that is required to introduce 0.01% micro-scale plastic strain. This is the deviation calculated in Fig. 4 (b). Equation 7 provides a second choice to measure 220 irσ , determined from the 0.01% micro-scale plastic strain, using the DEC for {220} grain family given in Table 3. Total true axial strain accumulated at high temperature, % 0 1 2 3 4 5 6 7 8 Internal resistance, MPa 0 100 200 300 400 500 600 700 Equation 5 Equation 6 Equation 7 Total true axial strain accumulated at high temperature, % 0 1 2 3 4 5 6 7 8 Internal resistance, MPa 0 100 200 300 400 500 600 700 Equation 5 Equation 6 Equation 7 (a) (b) Figure 7. Internal resistance in specimens subjected to prior deformation at high temperature: (a) internal resistance without knowledge of internal stress; (b) internal resistance with knowledge of internal stress
RkJQdWJsaXNoZXIy MjM0NDE=