Hello Team, I would like to calculate the strain at a node #5 in a direction (l1,m1,n1) in the turbine blade FE model as shown. This node is connected with four elelemnts (#1,#2,#3,#4) and I have displacements of all the nodes of these elements in the Cartesian coordinate system.
I have tried to transform these displacements in the direction of 1.
Direction 1 and 2 are in-plane directions.
How to include the curvature effect into this strain? I want to do these calculation in excel or using python.
Work done so far:
We have Nodal displacements in Global cartesian coordinate system and then we have transformed in the plane (in the direction 1 and 2 as shown) then we have calculated the strain using the strain-displacement relation using the shape functions at the 2x2 gauss points. Then we have extrapolated these strains to the node 5 and then taken the average.
As the curvature of the Blade increases, the strain calculated using the above menthod differs more compared the value predicted by Gage Map tool.
For the flat plate or very small curvature, the results matches very well.
I think, we are miising the effect of curvature in the strain-displacement relation. How to take in to account the curvature effect?
Please help me.
This depends on the FEA software used. You can transform the nodal point strain into the reference system, e.g. in PERMAS you might use
NEW
INPUT
READ PERMAS FILE =
RETURN
TASK
EXEC
ACT SIT = STEP_1
STATIC
GEN NODAL POINT STRAIN
SELECT
TRANSFORM NODAL POINT STRAIN TO RSYS = 1 RESULT = NPSTR
EXPORT
ITEM CLEAR
ITEM NODAL POINT STRAIN BOOK = NPSTR
GO PERMAS BINARY
TASK END
STOP
I think a simple Lagrangian interpolation will work.
The curvature effect will automatically be included, if you know global coordinates of the nodes in 3D space.
And the calculation can be done in excel if is Lagrangian interpolation.
Still would love to be corrected if this approach is wrong.
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