Principal Strains:

If the state of stress is given in terms of the principal stress components σ₁, σ₂ and σ₃, the corresponding strains components may be calculates as,

ε₁ = σ₁/E -v(σ₂/E -v(σ₃/E))                                                                                          . . . (21)

ε₂ = σ₂/E -v(σ₁/E -v(σ₃/E))                                                                                          . . . (22)

ε₃ = σ₃/E -v(σ₁/E -v(σ₂/E))                                                                                          . . . (23)

Alternately, we may rewrite as,

Using abbreviations, [ε] for , [σ] for  and [C] for 1/E

[ε] =[C] [σ]

Eq. will be useful in writing compact expressions and simplified derivations.