Yield Stress According to Ludwik
| Yield stress | kf | = | MPa |
| Strain hardening constant | C | = | MPa | |||
| Natural strain | φ | = | ||||
| Strain hardening exponent | n | = |
For unalloyed and low-alloy steels, the yield stress depends on the material in question. In addition, it is influenced by the condition, the pre-treatment, the natural strain, the deformation speed and the deformation temperature.
A low yield stress reduces the restoring moment caused by springback effects and thus leads to better shape retention.
| Strain hardening constant | C | = | MPa |
| Tensile strength | Rm | = | MPa | |||
| Strain hardening exponent | n | = |
The material-specific constant C can be approximately estimated using the tensile strength and uniform elongation from the tensile test.
A disadvantage of the Ludwik equation is the infinite slope e at φ0. The Swift approach offers an improvement.
The Ludwik equation is valid for natural strains ≤ 1 and room temperature, but is not suitable for high-alloy steels and copper.
The following applies to cold-formed steel and Al alloys in the range of φ = 0.2... 1:
In a double logarithmic network, the flow curves can be approximated by a straight line with the slope n (from the material table).