The Ramberg–Osgood equation was created to describe the non linear relationship between stress and strain—that is, the stress–strain curve—in materials near their yield points. It is especially applicable to metals that harden with plastic deformation (see work hardening), showing a smooth elastic-plastic transition. As it is a phenomenological model, checking the fit of the model with actual experimental data for the particular material of interest is essential. In its original form, the equation for strain (deformation) is here is strain, is stress, is Young's modulus, and and are constants that depend on the material being considered. In this form K and n are not the same as the constants commonly seen in the Hollomon equation. The equation is essentially assuming the elastic strain portion of the stress-strain curve, , can be modeled with a line, while the plastic portion, , can be modeling with a power law. The elastic and plastic components are summed to find the total strain. The first term on the right side, , is equal to the elastic part of the strain, while the second term, , accounts for the plastic part, the parameters and describing the hardening behavior of the material. Introducing the yield strength of the material, , and defining a new parameter, , related to as , it is convenient to rewrite the term on the extreme right side as follows: Replacing in the first expression, the Ramberg–Osgood equation can be written as Hardening behavior and yield offset In the last form of the Ramberg–Osgood model, the hardening behavior of the material depends on the material constants and . Due to the power-law relationship between stress and plastic strain, the Ramberg–Osgood model implies that plastic strain is present even for very low levels of stress. Nevertheless, for low applied stresses and for the commonly used values of the material constants and , the plastic strain remains negligible compared to the elastic strain. On the other hand, for stress levels higher than , plastic strain becomes progressively larger than elastic strain. The value can be seen as a yield offset, as shown in figure 1. This comes from the fact that , when . Accordingly, (see Figure 1): elastic strain at yield = plastic strain at yield = = yield offset Commonly used values for are ~5 or greater, although more precise values are usually obtained by fitting of tensile (or compressive) experimental data.