Fall 2008, MET 425 - FEA Applications II
Prof. Dave Johnson, dhj1@psu.edu
Penn State - Erie, The Behrend College
HW-2A: P-element Model
Concepts:
- CAD model import to FEA (IGES file)
- Taking advantage of geometric and load symmetry
- Definition of P-Method finite elements
- Different considerations for meshing, solving & postprocessing
P-elements
- Application of strength of materials concepts
(MCH T 213 and MET 320)
- ANSYS, not Workbench
A plastic latch part is shown in the figure above. Young's modulus is
350,000 psi, Poisson's ratio is 0.40
This part was modeled in Pro/ENGINEER for training
purposes. You may click here to access
the IGES
File
BETTER YET: Use a Right-click on this link, then "Save Target
As...", then "Save as type: All Files", and use a file name like:
"latch.igs"
The part is fixed to a wall on the vertical flat
(left) face
The sharp edge of the catch must be depressed
0.25" to engage/disengage the latch.
In Solution, don’t forget to set local
convergence points for solution accuracy
Hand calculation:
- Estimate the force required to bend a similar
"cantilever" beam by 0.25" and compare this to the FEA model
reaction total Fy on the edge of the sloped face of the latch
- Estimate the max. normal stress on the the top face of
the latch, beyond the 0.75" fillet (using the bending force, Fy from
the FEA solution). Compare it to the proper FEA results plot to validate your model.
[This requires "scoping" but in ANSYS we use "Selecting." The sum of
forces in Y will equal zero for the whole model since the wall reaction will
balance the applied load. Select either half of the model to get the
reaction force value]
Turn in:
- Hand calc data for approx. MOI, estimated
Force, and sx
- a plot showing the P-element mesh
- a plot showing ALL loads and constraints (environment)
- a plot showing the p-convergence points on the model
[Note: convergence points can be labeled on either
the element plot or the env. plot]
- the p-convergence graph - EXPLAIN or
INTERPRET this plot. What does it show ?
- the p-level plot
- a plot showing the highest equiv. stress on the part
[Note: p-element stresses & deflections cannot
be plotted until you "Read Results"]
[Note: if stress contours are jagged - either explain why or fix it (/EFACET)]
- a stress plot to compare to the hand calc
stress
- a reaction force summary to compare to the
estimated hand calc force.
Why are the first two images exhibiting jagged
stress contours ?
[One - wrong result 'Element Solution' (NOAVG);
Other - low element face faceting]
Is the 3rd contour plot better ?
[YES - increased facets, smoother contours]
Interpret the Convergence History graph ?
Display showing P-Convergence Control Points:
