Hosford yield criterion

The Hosford yield criterion is a function that is used to determine whether a material has undergone plastic yielding under the action of stress.

Hosford yield criterion for isotropic plasticity

The Hosford yield criterion for isotropic materials^[1] is a generalization of the von Mises yield criterion. It has the form

${\displaystyle {\tfrac {1}{2}}|\sigma _{2}-\sigma _{3}|^{n}+{\tfrac {1}{2}}|\sigma _{3}-\sigma _{1}|^{n}+{\tfrac {1}{2}}|\sigma _{1}-\sigma _{2}|^{n}=\sigma _{y}^{n}\,}$

where ${\displaystyle \sigma _{i}}$, i=1,2,3 are the principal stresses, ${\displaystyle n}$ is a material-dependent exponent and ${\displaystyle \sigma _{y}}$ is the yield stress in uniaxial tension/compression.

Alternatively, the yield criterion may be written as

${\displaystyle \sigma _{y}=\left({\tfrac {1}{2}}|\sigma _{2}-\sigma _{3}|^{n}+{\tfrac {1}{2}}|\sigma _{3}-\sigma _{1}|^{n}+{\tfrac {1}{2}}|\sigma _{1}-\sigma _{2}|^{n}\right)^{1/n}\,.}$

This expression has the form of an L^p norm which is defined as

${\displaystyle \ \|x\|_{p}=\left(|x_{1}|^{p}+|x_{2}|^{p}+\cdots +|x_{n}|^{p}\right)^{1/p}\,.}$

When ${\displaystyle p=\infty }$, the we get the L^∞ norm,

${\displaystyle \ \|x\|_{\infty }=\max \left\{|x_{1}|,|x_{2}|,\ldots ,|x_{n}|\right\}}$. Comparing this with the Hosford criterion

indicates that if n = ∞, we have

${\displaystyle (\sigma _{y})_{n\rightarrow \infty }=\max \left(|\sigma _{2}-\sigma _{3}|,|\sigma _{3}-\sigma _{1}|,|\sigma _{1}-\sigma _{2}|\right)\,.}$

This is identical to the Tresca yield criterion.

Therefore, when n = 1 or n goes to infinity the Hosford criterion reduces to the Tresca yield criterion. When n = 2 the Hosford criterion reduces to the von Mises yield criterion.

Note that the exponent n does not need to be an integer.

Hosford yield criterion for plane stress

For the practically important situation of plane stress, the Hosford yield criterion takes the form

${\displaystyle {\cfrac {1}{2}}\left(|\sigma _{1}|^{n}+|\sigma _{2}|^{n}\right)+{\cfrac {1}{2}}|\sigma _{1}-\sigma _{2}|^{n}=\sigma _{y}^{n}\,}$

A plot of the yield locus in plane stress for various values of the exponent ${\displaystyle n\geq 1}$ is shown in the adjacent figure.

Logan-Hosford yield criterion for anisotropic plasticity

The Logan-Hosford yield criterion for anisotropic plasticity^[2][3] is similar to Hill's generalized yield criterion and has the form

${\displaystyle F|\sigma _{2}-\sigma _{3}|^{n}+G|\sigma _{3}-\sigma _{1}|^{n}+H|\sigma _{1}-\sigma _{2}|^{n}=1\,}$

where F,G,H are constants, ${\displaystyle \sigma _{i}}$ are the principal stresses, and the exponent n depends on the type of crystal (bcc, fcc, hcp, etc.) and has a value much greater than 2.^[4] Accepted values of ${\displaystyle n}$ are 6 for bcc materials and 8 for fcc materials.

Though the form is similar to Hill's generalized yield criterion, the exponent n is independent of the R-value unlike the Hill's criterion.

Logan-Hosford criterion in plane stress

Under plane stress conditions, the Logan-Hosford criterion can be expressed as

${\displaystyle {\cfrac {1}{1+R}}(|\sigma _{1}|^{n}+|\sigma _{2}|^{n})+{\cfrac {R}{1+R}}|\sigma _{1}-\sigma _{2}|^{n}=\sigma _{y}^{n}}$

where ${\displaystyle R}$ is the R-value and ${\displaystyle \sigma _{y}}$ is the yield stress in uniaxial tension/compression. For a derivation of this relation see Hill's yield criteria for plane stress. A plot of the yield locus for the anisotropic Hosford criterion is shown in the adjacent figure. For values of ${\displaystyle n}$ that are less than 2, the yield locus exhibits corners and such values are not recommended.^[4]

References

See also

• Yield surface
• Yield (engineering)
• Plasticity (physics)
• Stress (physics)