Yield Stress & Flow Curve

The plastic flow of a metallic material occurs when permanent true strains occur due to a certain state of stress.

The yield stress k_f of a material describes the stress that is necessary in the uniaxial stress state in order to initiate and maintain permanent true strains.

In the uniaxial tensile test, the yield stress is determined by the tensile force F in relation to the respective specimen cross-section A.

The flow curve is the graphical representation of the yield stress k_f as a function of the main strain.9

In a double logarithmic network, the flow curves can be approximated by a straight line with the gradient n (from the table of materials ).

Various equations are available for approximating the yield stress :

• Yield stress according to Ludwik
• Yield stress according to Swift