Reading Shear Loads on BAR elements
Reading Shear Loads on BAR elements
(OP)
Hi,
I'm analyzing some fasteners modeled as bar elements, therefore I need to determine the tension and shear on the fastener.
FEMAP has output vectors shear forces (in both plane1 & plane2), this is confusing to me. Is this in both directions perpendicular to the bar?
I mean there is only one plane that goes across a cylinder, the other two are axial (not shear).
Thanks,
W





RE: Reading Shear Loads on BAR elements
the tird plane is of course the cross-section, yes?
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RE: Reading Shear Loads on BAR elements
Let's assume the cross-section of the bar is a circle, hence the whole thing is a cylinder.
Axis 1 runs through the cylinder's axis. 2 and 3 are perpendicular to the axis of the cylinder.
Since this is a fastener, I'm interested in reading tension and shear. The shear loads should be in directions 2 and 3 which form a plane of its own that cuts perpendicular to Axis 1.
FEMAP has output vectors shear forces (in both plane1 & plane2), I wish these were the loads in directions 2 and 3 from my example, but I'm not sure. Does anyone has a good understanding of these output vectors?
Thanks,
W
RE: Reading Shear Loads on BAR elements
In your example, to get the maximum transverse shear, you want the shear forces from both planes 1-2 and 1-3. Simple vector math will give the combined magnitude...from which max. shear stress is easy. There is no 2-3 shear for a 1-D beam/bar element...
Stated another way, ditch the computer, get out the pencil and paper, and draw the simple cantilever beam example problem from statics 101. Label your axes... 1 along the length of the beam, 3 up. The shear force due to the cantilever load is in plane 1-3.
Hope this helps...
RE: Reading Shear Loads on BAR elements
the shear in axis 2 and 3 is what FeMap (and NASTRAN) call plane 1 and 2. think of shear as in a panel, it affects the plane, not just a single direction (like tension). its the same with you fastener ... the shear is causing displacements in a plane. yes?
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RE: Reading Shear Loads on BAR elements
That's what I understood from your explanations and it would make sense as to why there is no such thing as shear in plane 3.
Hence, total shear would be SQRT( shear-plane1^2 + shear-plane2^2)???
Thank you :)
W
RE: Reading Shear Loads on BAR elements
plane 1 is defined by two axes, lets say 1 (axial) and 2 (transverse, up).
now a moment can cause deflection in plane 1 (ie the moment vector is normal to plane 1)
than moment can be a couple of shear forces, and the shear force direction would be along axis 2.
so plane 1 shear is along axis 2 and plane 2 along axis 3 ... clear as mud ??
look up the NASTRAN element library reference book, it shows the positive sign convention.
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RE: Reading Shear Loads on BAR elements
RE: Reading Shear Loads on BAR elements
shear is caused by a couple (isnt that ironic?)
hence, the plane defined by FEMAP (1 or 2), is the plane where that couple is acting.
Is that it?
RE: Reading Shear Loads on BAR elements
maybe try this, typically shear distorts a square into a rhombus, yes? the square is defined by a plane ...
or your fastener will deflect due to the shear force, in the direction of the shear force, defining a plane ...
btw, why use a bar for a fastener ? why not an RBE and a CBUSH ?
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RE: Reading Shear Loads on BAR elements
si?
I'm using BAR elements because the customer is always right :)
RE: Reading Shear Loads on BAR elements
bars are a bit nasty, in that they fix the ends making it harder to get the shear stiffness you want
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