4. Relaxation-fluid extrapolation method. Creep-relaxation comparison

As the operating time of industrial systems can sometimes be of the order of several decades, as in the case of nuclear power plants, creep tests of the same duration are not available at the time of structural design: extrapolation methods based on short creep tests are available [14] . Nevertheless, a large number of creep tests lasting several weeks, or even months, is still necessary for this dimensioning: the relaxation test allows, with a limited number of tests, to cover a wide stress σ - plastic strain rate range