Because the properties of aluminum alloys are dependent upon both the exposure temperature and also to the length of time of exposure, the prediction of design values for structures designed to last many years is a significant challenge. For relatively short-life structures, the need is addressed simply by planning ahead and carrying out a test plan that replicates the intended service conditions. This is feasible for structures whose design life might be as much as a year or even five years, but it is not very practical for structures for which the life expectancy is 10 years or more.

Since the early 1950s, the analyses of long time, high temperature data for aluminum alloys, ferrous metals and superalloys (1-4), has been addressed through the use of time-temperature parametric equations that permit the consolidation of data obtained over a variety of temperatures and exposure times into a single relationship. Once such relationships are established based upon the available experimental data and optimized, it is possible to extrapolate to service conditions substantially beyond the range of the test data themselves. This must always be done cautiously and with awareness of the extent of the extrapolation, but it provides a better perspective than simply extrapolating individual strength life curves.

Within the scope of this paper, the authors will briefly review the background for and the application of the most widely used time-temperature parameter, the Larson-Miller Parameter (LMP) plus, more importantly, demonstrate that there is value in the application of such parameters to types of data and performance characteristics beyond the creep-rupture data for which they are best known and most widely used.

Download pdf Application of Time-Temperature-Stress Parameter to High Temperature Performance of Aluminum Alloys