| The cyclic creep behavior of pure aluminum is investigated for two different types of testing machine, one is the creep testing machine having constant values of peak stress, stress amplitude and frequency, and the other is Instron machine controlling peak load constant. Temperature range of the tests is around 0.33 T_m. Both results from the two different machines show the cyclic creep acceleration for which the constant load condition is more significant. The activation energies for the creep and the measured internal stress are increasing with the strain but the values are always higher for the constant peak stress test. Since the lower internal stress is one of the representatives of softer substructure, it probably accounts For the more accelerated cyclic creep and the lower apparent activation energy for the creep test under constant peak load. It is thought that the significant deviation of the creep behaviors with Instron machine is due to the increasing stress amplitude and peak stress, and the difference in the initial loading rate. |
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