13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- Figure 8. Figure 7. Fracture surface, low cycle fatigue testing, test temperature 20°C. a) b) c) Figure 8. Crack patterns, low cycle fatigue, test temperature 20°C. In the figure, a) is 0° build direction, b) is 45° build direction and c) is 90° build direction. Loading direction is horizontal in the figure. At high temperature, the testing has been performed as thermomechanical fatigue testing in strain control using a trapezoid wave form with hold time at Tmax and a strain ratio Rε=0. Normalized results from the thermomechanical testing are presented in Figure 9. In the figure, the relative strain value “1” indicates the normalized strain for a hot-rolled material to yield a certain fatigue life. 0 0,5 1 1,5 2 2,5 3 0 90 direction relative strain [-] 450°C 800°C a) 0 0,5 1 1,5 2 2,5 3 0 90 direction relative strain [-] 450°C 800°C b) Figure 9. Normalized average data from thermomechanical fatigue test results. Strain measurements are relative to the strain that for a hot-rolled bar will yield a) 500 cycles and b) 1000 cycles. For comparison, the fracture surfaces have been evaluated and typical fracture patterns at 450°C and 800°C are presented in Figure 10 and Figure 11 respectively.
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