Anti-intrusion plate and Front Bulkhead

[FSS_Racing]

We were doing our test for the anti intrusion plate deformation and we had problem with the maximum deformation which is higher than 1". So we want to reinforce the intrusion plate by welding a 90° angle iron on the back of the intrusion plate. This angle iron will be welded on the intrusion plate and on the front bulkhead. We did not see anything in the rules that says that it is accepted or not allowed so we wanted to know what were your choice and what you think about this way to pass the test.

Thank you

[FSS_Racing]

We were doing our test for the anti intrusion plate deformation and we had problem with the maximum deformation which is higher than 1". So we want to reinforce the intrusion plate by welding a 90° angle iron on the back of the intrusion plate. This angle iron will be welded on the intrusion plate and on the front bulkhead. We did not see anything in the rules that says that it is accepted or not allowed so we wanted to know what were your choice and what you think about this way to pass the test.

Thank you

[BrendonD]

We didn't run into this problem, but an idea that was floated around was welding a diagonal tube onto the front of the bulkhead. Your compromise is stopping deflection at the expense of weight where you least want it.

[Nick Renold]

It really depends how you are mounting the attenuator. Our deformation was fairly low using a plate that was seam-welded onto the front bulkhead. This won't help you if your whole bulkhead buckles though.

Check out our youtube channel under the user "nufsae" to see videos of our attenuator tests.

[Demon Of Speed]

This will work to help reduce the maximum deformation of the anti-intrusion plate. However, some of the energy dissipation during the test was due to the anti-intrusion plate deforming, which may cause the same IA to not meet the acceleration requirements.

[Nick Renold]

The acceleration requirements are specified to be measured with the attenuator mounted to the anti-intrusion plate, so I do not think that will be an issue. You do not need to submit separate tests results for a mounted versus unmounted impact attenuator.

[Francis Gagné]

Firstly I am sorry for the confusion.

What my team mates have omitted to specify is that we are using the standard impact attenuator and therefore doesn't require the dynamics testing. Only static testing or analysis is needed. We decide to go down that route because the time we had was getting short to modify our impact attenuator testing rig to full scale 300kg and have it approved by the university was closing down, and the resources put into making it happen would not have been justifiable for our team size. Big enough static testing machine were available from the civil eng. labs.

On the fsaeonline website it is specified that :

Question 2: Rule B3.21.9 requires the attenuator to be mounted to the anti-intrusion plate and sets a maximum deflection for the plate. How should this be handled with the standard design?

Answer: To address this, teams should determine, either by testing or analysis, that their configuration for front bulkhead and anti-intrusion plate can support the required 117,720 N (26,755 lbf) of load from the anti-intrusion plate assuming a uniform pressure applied load across the area where the anti-intrusion plate mounts. These calculations or test data should be included in the impact attenuator data submission and should include predicted strength and deflections. Deflections must be less than the 25.4mm (1 inch) maximum called out in rule B3.21.9.

We have today succeeded in making an acceptable (Minimal rule thickness requirement) design meeting the deformation requirement. I'll will briefly explain it here for the future teams that would want to use the standard impact attenuator next year Michigan, or for a later competition.

We have used ANSYS to perform structural static analysis with multi-linear material (stress-strain curve). Since we had a previous plate testing we had an idea of the precision of the analysis. Our bulkhead is the exact same size as the impact attenuator (bizarre enough it's a coincidence!). So the uniform load is pretty representative. Analysis was non-linear with large deformation on and two time steps (1 with force from zero to full load, 2 with force from full load to zero) in order to account for springback.

The analysis conclusion were that :

-Plastic permanent deformation for a given material in the plate is about proportional to volume. Adding rigidity as my team mates have suggested give insignificant difference in the plastic domain.

-Higher yield point material makes a good difference in absorbing deformation energy.
-Limit condition of bottom edge as fixed (Pivot) seems to represent well the behavior of the weld.
-Aluminum sheet spring-back is non negligible.


Experiment conclusions :

-For this size of the impact attenuator, the minimum thickness steel sheet seam welded need to be in 4130 steel or better to pass.
-Bolted 6061-T6 aluminum 3/16" plate passed just by much, we had 2 times the predicted deformation, mostly because of the different limit conditions we think.
-Thick sheet of polystyrene foam sandwiched between plate and anti-intrusion plate spread the load pretty evenly as required.
-Analysis predicts well the shape of the deformation, but the total deformation can be way off.
-Experimental validation of the analysis is an absolute must if the used material stress-strain curve is not laboratory tested. And even with that, the FEA won't take into account weld HAZ.
-Static 40G deceleration is intense.

Best regards,

[df_fsmb]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Nick Renold:
It really depends how you are mounting the attenuator. Our deformation was fairly low using a plate that was seam-welded onto the front bulkhead. This won't help you if your whole bulkhead buckles though.

Check out our youtube channel under the user "nufsae" to see videos of our attenuator tests. </div></BLOCKQUOTE>

Nick, I just watched your youtube video of the IA test. (http://www.youtube.com/watch?v=0z-kOutrRas)

Is this the final test for this year's competitions?

Because I can't see the required 2inch of unsopported volume behind the anti-intrusion plate. How did you show that your plate does not penetrate into the cockpit?

[RANeff]

It would be this one:

(http://www.youtube.com/watch?v=c0_HoOd74xI&feature=related)

[BrendonD]

df_fsmb, that video wasn't our final test, that was just to experiment with the strain rate of the material under load. We did a dynamic test at a proper facility with the aluminum honeycomb mounted to a mockup of our front bulkhead with high speed cameras filming the whole thing.

That's this video here: (watch?v=c0_HoOd74xI) paste this in after the you tube dot com in the address bar.

Hope that helps.

[Swayam Ray]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Francis Gagné:
Firstly I am sorry for the confusion.

What my team mates have omitted to specify is that we are using the standard impact attenuator and therefore doesn't require the dynamics testing. Only static testing or analysis is needed. We decide to go down that route because the time we had was getting short to modify our impact attenuator testing rig to full scale 300kg and have it approved by the university was closing down, and the resources put into making it happen would not have been justifiable for our team size. Big enough static testing machine were available from the civil eng. labs.

On the fsaeonline website it is specified that :

Question 2: Rule B3.21.9 requires the attenuator to be mounted to the anti-intrusion plate and sets a maximum deflection for the plate. How should this be handled with the standard design?

Answer: To address this, teams should determine, either by testing or analysis, that their configuration for front bulkhead and anti-intrusion plate can support the required 117,720 N (26,755 lbf) of load from the anti-intrusion plate assuming a uniform pressure applied load across the area where the anti-intrusion plate mounts. These calculations or test data should be included in the impact attenuator data submission and should include predicted strength and deflections. Deflections must be less than the 25.4mm (1 inch) maximum called out in rule B3.21.9.

We have today succeeded in making an acceptable (Minimal rule thickness requirement) design meeting the deformation requirement. I'll will briefly explain it here for the future teams that would want to use the standard impact attenuator next year Michigan, or for a later competition.

We have used ANSYS to perform structural static analysis with multi-linear material (stress-strain curve). Since we had a previous plate testing we had an idea of the precision of the analysis. Our bulkhead is the exact same size as the impact attenuator (bizarre enough it's a coincidence!). So the uniform load is pretty representative. Analysis was non-linear with large deformation on and two time steps (1 with force from zero to full load, 2 with force from full load to zero) in order to account for springback.

The analysis conclusion were that :

-Plastic permanent deformation for a given material in the plate is about proportional to volume. Adding rigidity as my team mates have suggested give insignificant difference in the plastic domain.

-Higher yield point material makes a good difference in absorbing deformation energy.
-Limit condition of bottom edge as fixed (Pivot) seems to represent well the behavior of the weld.
-Aluminum sheet spring-back is non negligible.


Experiment conclusions :

-For this size of the impact attenuator, the minimum thickness steel sheet seam welded need to be in 4130 steel or better to pass.
-Bolted 6061-T6 aluminum 3/16" plate passed just by much, we had 2 times the predicted deformation, mostly because of the different limit conditions we think.
-Thick sheet of polystyrene foam sandwiched between plate and anti-intrusion plate spread the load pretty evenly as required.
-Analysis predicts well the shape of the deformation, but the total deformation can be way off.
-Experimental validation of the analysis is an absolute must if the used material stress-strain curve is not laboratory tested. And even with that, the FEA won't take into account weld HAZ.
-Static 40G deceleration is intense.

Best regards, </div></BLOCKQUOTE>

Please can you tell me how did you mount the Standard Impact Attenuator to the Anti Intrusion Plate??

[Francis Gagné]

We glued the foam directly to the AI Plate with epoxy resin.