History of the Development of Constitutive Equations for Strain-Rate-Metry from Microstructures

The measurement of strain rate (strain-rate-metry) from microstructures started in early 1970s. Earlier the strain rate was measured from the constitutive equations for stress-temperature-strain rate relations formulated from laboratory experiments. Later the term of water fugacity was included in these constitutive equations. In the late 1990s, a new model was formulated to measure strain rate from the shape of the recrystallized quartz grains, by measuring their area-perimeter fractal dimensions. This review describes the history of development of the different models of strain-ratemetry over the last five decades.