13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- compressive when the temperature is above the threshold for time dependent crack growth to become active i.e. the value of da/dt is always zero in the simulation. Therefore, simulation results for cycles 1 and 3 are effectively dependent only upon the fatigue cycle which occurs during the load cycle. This fatigue cycle is the same for cycles 1 and 3 and so the simulation results for cycles 1 and 3 are identical in Figure 10. The test results for these two cycles are also similar and show good agreement with the simulation. Cycle 4d presents a more interesting case as the temperature is above the threshold for time dependent growth for about 80% of the cycle duration and during this time the load is either increasing, at maximum hold value or decreasing. Therefore time dependent growth can be expected. Simulation results for all cycles are shown in Figure 11. On this scale, cycle 4c appears to have the same result as cycle 4d. However, the cycle 4c result is slightly higher. This is the expected outcome since, although the temperature histories for the cycles are the same, cycle 4c has a longer period at maximum load than cycle 4d and hence more time dependent growth is expected. The additional time dependent growth is however relatively small as the extra time at maximum load is in the region close to the temperature threshold for time dependent growth (i.e. da/dt will be small even if K is high). The result for cycle 4a falls above cycle 4b. Again this is not an unexpected result: cycle 4a has a longer period than 4b with extra time spent accruing time dependent growth at high temperature. Cycle 4a falls below 4c. The maximum load level for 4a is lower than for cycle 4c but the period is greater. The trade-off between high load and longer duration in this case has the result that the high load short duration of cycle 4c produces a higher overall growth rate (i.e. higher da/dt values). 0.1 1 10 100 1000 10 100 Relative da/dN [/cycle] Kmax [MPasqrt(m)] Test data (cycle 3 ‐ isothermal 400C) Test data (cycle 1) Test data (cycle 3) Zencrack analysis (cycle 3 ‐ isothermal 400C) Zencrack analysis (cycle 1) Zencrack analysis (cycle 3) 1 10 100 1000 10 100 Relative da/dN [/cycle] Kmax [MPasqrt(m)] Test data Zencrack analysis Figure 10. Test and simulation results for cycles 1 and 3 (left) and 4d (right) 0.1 1 10 100 1000 10 100 Relative da/dN [/cycle] Kmax [MPasqrt(m)] Zencrack analysis (cycle 3 ‐ isothermal 400C) Zencrack analysis (cycle 1) Zencrack analysis (cycle 3) Zencrack analysis (cycle 4a) Zencrack analysis (cycle 4b) Zencrack analysis (cycle 4c) Zencrack analysis (cycle 4d) Figure 11. Simulation results for cycles 1, 3, 4a, 4b, 4c and 4d
RkJQdWJsaXNoZXIy MjM0NDE=