Crimp Die for 45 Primer and Cartridge -- FEA non-linear Analysis not matching with Real life results

[MechEngineerNT]

Hey Guys,


I'm running a quasi-static non-linear FEA in Ansys trying to simulate crimping a primer into the cartridge using a die crimp tool. In short, the crimping operation works in real life (80 units tested), to which I've decided to try to simulate. However, the result of the simulation isn't matching up with the real life results. I've put in all the right material properties of a 7075-T6 aluminum, and have also put in the bi-linear curve to simulate strain hardening. In the attachment, you can see I'm above the ultimate strength of the material when the die crimp compresses the flange. Is this because of the contact stresses??? Why does it work in real life, but the simulation isn't showing it, instead failure? This has been giving me hell!

Thanks

 

[NRP99]

The reasons behind difference in real life results and analysis results not matching is real geometry defects such as out of roundness, real material defects, simulation material assumption(such as bi-linear hardening in your case) and simulation geometry difference from actual geometry, contact non-linearity.

Refine the mesh at the contacting surfaces further. Use structured mesh. Use proper contact algorithm such as frictional contact with Augmented Lagrange. Use multi linear hardening. If results are incorrect, do explicit analysis.

This Link may be helpful.

 

[MechEngineerNT]

Thanks NRP99. That was very useful. Did what you advised, but still got similar results, still failing, however FOS to ultimate is around 0.87 using Equivalent Von Mises now. I'm wondering if I should use a different failure criterion. The upper portion of the crimp is in compression, couldn't imagine that being the failure mode.

 

[rickfischer51]

Is that an axisymmetric model or plane stress/plane strain? Have you taken into account work hardening from previous forming operations and rolling direction in raw brass sheet? Which bilinear curve and how flat is the tangent modulus? Do you have a complete stress/strain curve for your raw material? Does your bilinear curve match your stress/strain curve out to the max strain you see in your simulation? Dont look at ultimate stress, look at strain.

Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[L_K]

Following article could be related to your simulation:

https://caeai.com/blog/incorporating-stress-triaxiality-factor-fea-simulations