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Excessive distortion of continuum shell elements

Excessive distortion of continuum shell elements

Excessive distortion of continuum shell elements

(OP)
I'm modeling FRP strengthened steel tubes under impact loading. I have used continuum shell elements as FRP composites and cohesive elements as epoxy adhesive. However, I'm getting error due to excessive distortion of continuum shell element away from the impact zone. Please find the attached picture to see the distorted element. I can not understand why elements are distorting away from the impact zone. The mesh size in impact zone is around 5*10 and 25*10 in away from impact zone.

RE: Excessive distortion of continuum shell elements

Have you applied any hour-glassing control?

RE: Excessive distortion of continuum shell elements

(OP)
I kept hourglass control as default setting in element definition. Do I need to change it to other type of control (e.g Enhanced)?
Thanks a lot.

RE: Excessive distortion of continuum shell elements

Try it, also a visual inspection of the mesh to see if any areas look hourglassed.

Another option maybe mass scaling if hourglass control has no effect.

RE: Excessive distortion of continuum shell elements

If you start adding HG control and mass scaling you then want to make sure your artificial and kinematic energies are remain small compared to internal energy.

RE: Excessive distortion of continuum shell elements

(OP)
Thanks all for your valuable input in my modelling. Now I can avoid excessive element distortion/rotation of continuum shell elements using stiffness hourglass control and mass scaling of continuum part. The energy produced for mass scaling is less than 2% of internal energy. Also the artificial energy is around 3% of internal energy. Could you please let me know that what else energy comparison I should check to confirm the accuracy of the simulation?

One more thing, Once I'm starting mass scaling of continuum shell element, no element of continuum shell part is failing or removing from the model. without mass scaling continuum shell elements were failed/removed from the model with same impact mass and velocity.

Many Thanks.

RE: Excessive distortion of continuum shell elements

Since this is an impact problem, inertial forces will play a role in the solution, so the kinetic energy does not necessarily need to remain small compared to internal energy. What's more important when using mass scaling on a dynamic impact problem is to make sure the mass scaling isn't significantly increasing your overall mass, since that will artificially increase your inertial forces. As the job runs, the status file reports the "percent change mass." I typically make sure it remains below 1%. If it's above that, then you need to reduce the mass scaling. If you are adding too much mass scaling, and hence artificially increasing the tube's mass, then the tube will resist the impact better. This may be why you no longer have elements failing.

When running an explicit analysis, the only time you need to make sure kinetic energies remain small compared to internal energy is when you are running a quasistatic analysis.

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