Do these mean shear and stress in the respective directions? 1

[drennon236]

The first three mean stress in the first, second and third direction, for example in the x, y and z direction:

What would the last three numbers mean -(23,32) , (13,31) , (12,21)? I understand that they represent shear, but how does it work with directions? Are there any good illustrations of this?

 

[TGS4]

If X = 1, Y = 2, and Z = 3 (in your typical coordinate triad), then:
σ₁₁ is the (normal) stress on the X face in the X-direction
σ₂₂ is the (normal) stress on the Y face in the Y-direction
σ₃₃ is the (normal) stress on the Z face in the Z-direction
σ₁₂ is the (shear) stress on the X face in the Y-direction, while σ₂₁ is the (shear) stress on the Y face in the X-direction
σ₂₃ is the (shear) stress on the Y face in the Z-direction, while σ₃₂ is the (shear) stress on the Z face in the Y-direction
σ₁₃ is the (shear) stress on the X face in the Z-direction, while σ₃₁ is the (shear) stress on the Z face in the X-direction

 

[TGS4]

The stress tensor is a 3 X 3 matrix, with the normal stresses on the diagonal. The tensor is symmetric, so σ₁₂ = σ₂₁, and so on.