Q. Factors in the design of high temperature materials?

There is typically little correlation between room temperature strength and high temperature strength of creep-resistant materials. The design criteria for the ‘High Temperature' range, where a material's plastic properties predominate, are based on the allowable stresses for a specified creep rate.

Tests for measuring these properties may include creep, stress-rupture or creep-rupture tests. If only the rate of deformation is measured, it is considered a creep test. If only time to rupture is measured, it is a stress rupture test. If both the deformation and the time to rupture are measured, it is a creep rupture test.

The rate of deformation over a long period of time is referred to as the creep rate. The stress rupture test will typically be carried out at a higher load (therefore higher creep rate) than a creep test so that the time to failure can be completed within a reasonable period of time.