Finding Shear Stress with a 2x2 Stress Tensor and Normal Vector

So, in summary, for a 2x2 stress tensor and a normal vector n, the shear stress can be calculated using either Pnt = Pn - Pnnn or n cross Pn, with the absolute value being the same in both cases but the direction being different.
  • #1
MaxManus
277
1

Homework Statement


If I have a 2x2 stress tensor and a normal vector n and want to find the shear stress. Is it the same which shear stress I find?

I mean
Pn = P dot n
Pnn = Pn dot n
Shear stress = Pnt = Pn - Pnnn
This gives Shear stress with the same unit vectors as n, f.ex i an j
But I can also use:
Shear stress = n cross Pn.
But this can give the shear stress with direction k

I believe the absolute value of the shear stress is the same in both cases.

The Attempt at a Solution

 
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  • #2
Yes, the absolute value of the shear stress will be the same in both cases. The only difference is that the direction of the shear stress will be different. In the first case, the shear stress will be in the same direction as the normal vector n, while in the second case, the shear stress will be perpendicular to the normal vector.
 

1. What is shear stress and how is it related to a 2x2 stress tensor?

Shear stress is a type of stress that occurs when two forces act in opposite directions parallel to a surface. It is related to a 2x2 stress tensor because it represents the shear components of the stress on a specific surface.

2. How is a 2x2 stress tensor calculated?

A 2x2 stress tensor is calculated using the normal and shear stresses acting on two perpendicular axes. The normal stress is the force per unit area acting perpendicular to the surface, while the shear stress is the force per unit area acting parallel to the surface.

3. What is the significance of the normal vector in finding shear stress?

The normal vector is important because it represents the direction of the surface on which the shear stress is being calculated. It is used to determine the orientation of the stress tensor and to accurately calculate the shear stress on that specific surface.

4. Can a 2x2 stress tensor be used to find shear stress on any surface?

No, a 2x2 stress tensor can only be used to find shear stress on surfaces that are perpendicular to the two axes being considered. For other surfaces, a different stress tensor or method may be required.

5. How is the shear stress value calculated from a 2x2 stress tensor?

The shear stress value can be calculated using the formula τ = σ*sinθ, where τ is the shear stress, σ is the magnitude of the normal stress, and θ is the angle between the normal vector and the direction of the shear force. This formula is based on the trigonometric relationship between the normal and shear stresses on a surface.

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