Flow law
Plasticity in forming

Having specified which states of stress can generate plastic deformation, we now need to specify how it takes place: this is the subject of the flow law.

If we consider figure 8 c in the [42] file, we see that the uniaxial stress state σ₀ corresponds to the entire possible range of plastic deformations ε. This means that, unlike in elastic behavior where (small) strain and stress are linked one-to-one (cf. relations (22) and (27) in the [42] file), the same cannot be said during plastic deformation. As with any irreversible phenomenon, the final state of the material, after plastic deformation, must depend on its entire previous history, which means that we need to find out how the state of stress σ, at a given instant, determines the tensor of strain rates $\stackrel{}{}$