FEA validation with hand calculations for shear stress

[bg1986]

Hi all,

I am currently doing an analysis, in which a circular part(rod) exerts load on another circular part(plate) concentrically.

I want to check the FEA results, with hand calculations for basic shear stress calculations.

For, hand calculations, the shear area would be
=axial load on the rod/( rod circumference * thickness of the plate. )

But, for comparison in FEA, what is the value i should be comparing with?

is it T(r,z)or T(Theta,Z) or combined value of these two values?( where as r-radial, theta-tangential and z- axial directions in cylindrical coordinate system).

I appreciate your help,

Thanks,
BG

 

[rb1957]

i'm not sure what area "rod circumference * plate thickness" gives you.

isn't shear stress in the bolt just P/A ?

or are you interested in plate bearing stress, area = diamter*thickness ?

another day in paradise, or is paradise one day closer ?

 

[rb1957]

or are you dealing with a large diameter pipe ? (in which case, circumference*thickness is shear area; but i wouldn't've called it a "rod" ?

another day in paradise, or is paradise one day closer ?

 

[bg1986]

Hi rb1957,

thanks for the reply,

i am trying to find a way to check the FEA i am doing with hand calculations, for the parts in the picture.

I like to know which shear stress value, when we compute should be considered from the results. ( this is considering in general for any FEA analysis, but, will help me understand it from this specific case).

-BG

 

[rb1957]

i don't think there's a general "one size fits all" check; you need to find some place in the model where a simple calc can be done and reasonably reflect all the complications that FEA is doing.

in your case, is the disc loading the rod in torsion ? is the rod modeled as solid elements or a beam ? which plane is the plane reacting the torque ?

another day in paradise, or is paradise one day closer ?

 

[bg1986]

there is no torque applied,but only axial load on the rod/pipe structure.

the plate structure is fixed at it's circumference.

I am modeling it in Ansys Workbench with solid elements.

the diameter of the rod/pipe is 1.5 inch and the thickness of the plate is .1 inch.

An axial load of 1000 lbf is applied on the rod.

So, i am trying to do comparision for the shear stress induced from hand calculations and FEA ( which i calculated as 1000/(pi* 1.5 * .1) == 2122 psi).

When i have finished the analysis, i am not able to capture this value in the FEA.

 

[rb1957]

ok, you got the correct shear in the disc; it wasn't clear from your original post.

how have you modeled the disc ? 2D plate elements, 3D solid elements ?

how have you modeled the rod ? 1D beam element, or 3D solid ?

if 3D solids, then you may have trouble seeing the stress you want to see, unless you've designed the mesh to show this stress, ie having a face of the elements oriented to the outer surface of the rod. if you made the rod protrude through the disc (so the disc is like a donut, with a hole in the middle) and "weld" the two components together (using common nodes along the join) then you should see it.

this is a bit of a nothing check, you're applying the load to the rod and now you're seeing the load leave the rod, going into the disc. ok, but it's got nowhere else to go.

you could do a force balance, don't know what ANSYS calls it, in NASTRAN its GPFB) at each node common to the rod and the plate, summ the forces along the applied load direction.


another day in paradise, or is paradise one day closer ?