According to Tresca's maximum shear stress criterion, plastic deformation occurs when maximum shear stress is equal to K, where K is equal to:(where σ1, σ2, σ3 are principal stresses and also σ1 ≥ σ2 ≥ σ3)
1
(σ1 + σ3)/2
2
(σ1 - σ3)/2
3
(σ1 + σ2)/2
4
(σ1 - σ2)/2