Changing Temperature Load with Constant Aging Mechanisms

2 Changing Temperature Load with Constant Aging Mechanisms 

With an existing temperature-time profile, the time-temperature shift cannot be directly determined using the Arrhenius equation. In order to apply this approach, however, it is necessary to presume maximum service temperature for the entire service life. This approach would result in considerably over-dimensioned parts [104]. 

A better approach is to consider the individual time-temperature intervals of the given time-temperature profiles separately, and to use a weighted evaluation of these intervals regarding their contribution to the aging process in the component [104]. This procedure is analogous to the degradation accumulation hypothesis by Miner s rule, Eq. 1.7. 

Every time-temperature interval is now associated with a degradation value according to Eq. 1.7. The sum of all degradation values corresponds to the total degradation of the material [104]. 

If the quotient of load time and failure time at the corresponding temperature is replaced by the reference time at elevated temperature, degradation accumulation can be formulated as  

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