Laminate Layup and Simulate Results
We have found problems when analyzing FEM results of laminate layups. The problems occur when you have forces in normal direction of a laminate layup. I will show a simplified model below to show you the problem and then I hope you can guide me to a solution.
Model: Composite beam. Fully constrained at one side and a normal force of 10 N at the other side. A surface of 20 mm width x 600 mm long is creating the test object. This surface is simplified as a shell with a composite laminate attached to it.
The laminate consists of two 1 mm layer.
Results according to von Mises shows:
Same stresses as hand calculations are obtained (225 MPa at the middle of the beam). No problems so long.
Now to the problem. When you are running a composite analyze you want to analyze the results in failure-index, not von Mises. Failure-index compares tensile and compressive stresses against specified limits in the material data.
Following is obtained when showing maximum failure-index results at all plies:
Failure index = 0 at the hole beam.
Following is obtained when showing maximum failure-index results at ply 1:
Failure index = 0.9 at the center of the beam. Correct value in compression (225/250 = 0.9).
Following is obtained when showing maximum failure-index results at ply 2:
Failure index = 0 at the hole beam.
Changed force direction:
If I change the direction of the force, to opposite direction, following results are obtained.
- Same results when looking at all plies.
- Ply 1 is changed from compression to tensile. A new Failure Index is generated of 0.45 (225/500), at the middle of the beam. The value is correct according to tensile limit.
- Same results when looking at ply 2.
Conclusion:
- Failure Index – Maximum – of all plies: do not find the highest Failure index.
- Failure Index – Maximum – of ply top/bottom – Ply Number 2: is not analyzing both sides of the ply, even when it says “of ply top/bottom”. It should give a Failure Index of 0.45 (225/500).
- Different results when flipping force direction. From compressive to tensile.
Question:
Does anyone understand why Creo is generating these results? We really hope we can find a logical explanation to be able to rely on future results. We really appreciate all the help we can get!