The Larson-Miller Method

The Larson-Miller method is applicable to a variety of materials, including ceramics, and is most commonly used because of its simplicity. This relation is given as  

T is given in degrees Rankin (i.e., °F - - 460), t in hours and the constant C 20. The value of C seems to be applicable to many cases and materials, but deviation from this value has been observed and its value may be in the range of 15-30, depending on the material. Selecting the proper C value, which may be 

Assuming that the creep-strain-to-rupture, e, is a constant over the temperature range of interest and, if the strain is predominantly in the steady-state creep regime, then the average creep rate for the specimen lifetime to rupture, namely, tj, is given by  

P = T(C -I- Intf) is the Larson-Miller parameter [henceforth LMP] and is f( r). Under the assumption that activation energy is independent of applied stress, this equation may be used to relate the difference in rupture life to differences in temperature for a given stress. In many cases, C is indeed 20, which is obtained from the intercept with the logt axis of a logt, versus 1/T plott (Fig. 6.111). The slope of such a plot, namely Q/k (=P), is a function of stress, as seen in the schematic Fig. 6.111. For a graphic presentation, Eq. (6.102) may be written as  

The Larson-Miller parameter, P, in Eq. (6.102), is one of the useful parameters used for predicting creep life in metallic materials, but it is useful for ceramics as well. The LMP may be used to describe the stress-temperature-life relation in a SiC/SiC composite by means of the following expression  

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