Values for can also be found by means of fitting to experimental data, although for some materials, it can be fixed in order to have the yield offset equal to the accepted value of strain of 0.2%, which means: Alternative Formulations Several slightly different alternative formulations of the Ramberg-Osgood equation can be found. As the models are purely empirical, it is often useful to try different models and check which has the best fit with the chosen material. The Ramberg-Osgood equation can also be expressed using the Hollomon parameters where is the strength coefficient (Pa) and is the strain hardening coefficient (no units). Alternatively, if the yield stress, , is assumed to be at the 0.2% offset strain, the following relationship can be derived. Note that is again as defined in the original Ramberg-Osgood equation and is the inverse of the Hollomon's strain hardening coefficient. See also Viscoplasticity#Johnson–Cook flow stress model References Mechanics Materials science