Strain Exponent
Empirical relationships define the secondary creep behavior of materials where the strain rate remains proportional to the applied stress raised to a specific exponent. Use of the norton power law is standard for assessing the durability of components that operate under constant mechanical loads at high temperatures.
Physical Constancy
Laws link the rate of permanent deformation to the stress level and a temperature dependent coefficient. Within the norton power law, the exponent value reveals the underlying mechanism of the creep, such as dislocation glide or vacancy diffusion. Testing laboratories measure these values by applying a static weight to a material sample and recording the change in length over hundreds of hours.
Small variations in the alloy composition can lead to a measurable change in the exponent, which alters the predicted life of the part. Precisions in the load application and the measurement of the extension are required to produce a defensible norton power law model.
Mechanical Limit
Prediction accuracy is limited to the secondary stage of creep where the deformation rate is constant. Once the material enters the tertiary stage, the norton power law no longer describes the behavior of the sample accurately.
Longterm Integrity
Structural engineers rely on these calculations to set the inspection intervals for critical infrastructure. If the norton power law indicates that the strain will exceed the geometric tolerance, the part is scheduled for replacement.
