An attempt to predict remanent life based on creep time law

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The purpose of the present project is to examine the validity of a new method for the remanent creep life prediction and to make clear the characteristics of the new method based on the theta (i=1-4 )controlling the relationship between creep strain and time. To begin with, the new method (theta - projection concept) was applied to Ni base superalloy (IN-738). Here, it was made clear that the stress dependence of theta includes the change in cesistance due to the change in creep mechanisms and creep structures, which would take place when extrapolation is made over a wide range on stress. This fact demonstrates that the new method is superior to the current methods from various views. Thus, the accumulation of creep data in the new method was recommended.Secondly, the studies on the creep time law of a precipitation hardened aluminum alloy(2024) was conducted. Here, long-termed creep behaviors were predicted from the short-termed creep data and they were compared with the actual long-termed creep data. It was found that there existed the fairly well coincidence between the predicted and actual creep curves. The present analysis showed that the scatter of theta_2 was much larger than those of others when log theta_i s were plotted against stress. However, it was to be noted that the scatter did not seriously affect the accuracy of extrapolation. In order to elucidate why theta_2 has larger scatter, the error map, namely , the map showing the change in standard error with the change of two parameters out of four, two others being kept constant, was determined. Using the maps, the relationship among parameters and the reason of the large scatter were made clear. It was shown that the error maps of this kind would be generally applicable and halpful for predicting the remanent creep life.