Stress results in a cantilevered beam
Stress results in a cantilevered beam
(OP)
As I often do, I solve a simple problem with hand calculations then solve the same problem using FEA just to see how well they compare. When I FEA analyzed a simple rectangular cross-section cantilevered beam (with 2:1 the highest aspect ratio) with a vertical point load in the middle of the free end, I found that the highest stress does not appear at the wall, and, regardless of mesh density the highest stress is always one element away from the wall. Why is this?
Tunalover





RE: Stress results in a cantilevered beam
Cheers
Greg Locock
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RE: Stress results in a cantilevered beam
Greg's point is (I think) that you are constraining the nodes at the end of the beam so one face of an element cannot move.
Try this, constrain the restraint nodes only in the load direction (this should react 3 rigid body motions (if you've got a sea of nodes on the end of the beam). now pick nodes to constrain in the other directions ... what we call 3-2-1 constraint ... in your case 1 is the load direction (say X) at node X,Y,Z, then 2 is an X and Y constraint at a node X, Y, Z2; and 3 an X, Y, and Zat node X, Y2,Z ...
clear as mud ?
another day in paradise, or is paradise one day closer ?
RE: Stress results in a cantilevered beam
Yes I am constraining all the DOFs at the wall. But your method is hardly intuitive. Maybe if you can provide a sketch? That would be a big help.
Bruce Jackson
Tunalover
RE: Stress results in a cantilevered beam
do some research on minimal constraint for models.
lets say X and Y are the inplane directions, and Z is out of plane.
then at every node suppress Z ('cause every node should be reacting out-of-plane load)
This constrains 3 rigid body motions (yes?, if not, research "rigid body motion")
so you have 3 more to constrain (X, Y, and RZ; yes?)
constrain 2 nodes with different Y co-ord in X (to constrain Y and RZ)
constrain 1 node in X
this is commonly referred to as 3-2-1 constraints (one node is constrained in 3 directions, another in 2, and the third in 1).
another day in paradise, or is paradise one day closer ?
RE: Stress results in a cantilevered beam
I'm handwaving, FEA theory bores me to tears, but 35 years of experience with FEAers has led to a certain familiarity with the concepts.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Stress results in a cantilevered beam
Rick Fischer
Principal Engineer
Argonne National Laboratory