Help with understanding stress tensors

[MaxManus]

I'm taking a continuum mechanics course and we use the 3*3 stress tensor a lot. The problem is that I do not understand what each component mean.

What does the tension(P_n normal(P_nn and tangent(P_nt tension mean, or just P_xy?

 

[Mapes]

For a stress tensor \sigma, \sigma_{11} is the normal stress in the 1-direction and \sigma_{12} is the shear stress in the 1-2 plane. Does this answer your question?

 

[Wiemster]

The component \sigma_{ij} of the stress tensor \sigma is the force per unit area in the i-direction on a surface with normal in the j-direction. When the indices are the same, the force is normal to the surface so that it represents a pressure. When the direction of the first index is normal to that of the second, it represents a shear.

 

[MaxManus]

Thanks, does that mean that the Pn is the force per unit area in the i-direction on the normal surface and Pnn is the the normal force on the normal surface and Pnt is the the force in the normal direction on the tangent surface?

Pn = P dot n
pnn = P dot n dot n
Where P is the stress tensor and n is the normal.