13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- Figure 8 shows variation of residual stress distribution σyy along X-axis for 2024 Al-alloy at different preload levels. Residual stresses are in compression state up to a depth of 1.57 to 1.72 mm from the edge of the hole. It shows an increasing of compressive residual stress with increasing of preload levels at hole. Around distance of 4.5 mm, residual stresses become tensile stresses and difference is negligible. Distributions of residual stresses σyy along X-axis for 6061 T6 Al-alloy at specified preload levels, are shown in figure 9. No high difference of residual stress at edge of hole was shown. The residual stress in tension is maximal at 2 mm deep from the edge of the hole still; it is of the order of 30 MPa. Figure 9. Residual stress along X-axis for 2024 T351 Al-alloy Figure 10. Residual stress along X-axis for 6061 T6 Al-alloy -700 -600 -500 -400 -300 -200 -100 0 100 200 0,002 0,003 0,004 0,005 0,006 0,007 0,008 0,009 0,010 -500 -400 -300 -200 -100 0 100 0,002 0,003 0,004 0,005 0,006 0,007 0,008 0,009 0,010
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