frame analysis on ansys

[josh2417]

Hi,
we just modeled our frame and are using ansys for analyzing the stresses and deflections
1. front impact- fix front roll hoop and apply uniform load on front bulkhead. We using 20g times our whole car weight.
2. rear impact- fix main hoop apply uniform load on rear bulkhead. using 15g
3. side impact- fix one side of frame and apply load on opposite side. little unclear on load application point so applying on the side members. 10g
4. roll over- fix the lower part of frame and apply point load at topmost part of front roll hoop. 5g.
5. torsion- fix all the suspension points except one side and apply vertical load upwards? how much force?
static load- apply engine load on engine mounts, axle loads on suspension points? not sure about this.

Are we on the right path? Is this how to start? are the loads correct? If you guys find something wrong please do correct me. Thanks in advance. Cheers

Suspension team - 2012
GS Racing
MIT India

[RobbyObby]

If you're looking do an in depth analysis like this, read the "Alternate Frame Rules" section of the rulebook. It details the required loads and constraints for each major section on the car. But for the most part you are on the right track.

WHere are you getting your load numbers from? How do you know they are representative?

Also for your torsion test, you want to ideally analyze the hub-hub stiffness, often called "installed stiffness", rather than just fixing the suspension nodes. This will give you more representative results.

There are also several hundred posts on this very subject on these very forums. I would start there.

[josh2417]

RobbyObby,
Yes sure will read through.

Load numbers? We use our total weight of the car with driver to do analysis. Though 20g, 15g and 10g are all over the top, it gives us some good fos. When we did analysis with these we found max stress to be around 120MPA. While the max yield stress of ms 1020 is around 290MPA.

Torsion test yes, will definitely do that.

I did read up the other posts and will continue to dig them up.Thanks.
Cheers

Suspension Team-2012
GS Racing
MIT India

[shark.ashwa]

josh,

I don not know why you are doing an impact analysis for your frame, is it a new material you are trying out? Otherwise, impact analysis are pretty much of no use in FSAE other than helping you get to know your chassis' weak points better. Also your load cases seem too exagerrated, what reasoning are you going for such high forces.
AS you said , the max stress seen is around 120 MPa and the yield strength of the MS you are using is 290 MPa (too less in my opinion), you dont ned such a high safety factor even more so in impact analysis which is a very rare scenario (read almost never).
Just my opinion.

Regards,
Sharath

[josh2417]

Sharath,

We are actually participating in the 2012 SUPRA Sae man. And all that they require is the frame for the initial scrutiny. Im glad we have a high safety frame, will sure please the judges i hope.

But more importantly i wanted to know if the constraints and load application methods are correct.

but what do you mean by too less?

Anyways thanks for your advice. Cheers.

Suspension Team-2012
GS Racing
MIT India

[shark.ashwa]

In that case, it would be much worthwhile if you actually did some research on what the impact forces on a formula car would be rather than going for that high forces. The judges would be much more impressed if you could show them some actual loading scenarios (im guessing maybe a crash test at 40kmph with just your front bulhead, impact plate and bulkhead supports and correspondingly for others), shouldn't be too difficult in my opinion. Real world testing always beats simulation in my world.
Just my opinion....and good luck for SUPRA!

Regards,
Sharath

[josh2417]

Real world testing always beats simulation in my world.


Well said mate . And yes your 40km/hr makes more sense. And we are planning to calculate the load paths for the suspension loading cases as well.

And what exactly did you mean when you said, "too less" about the ms 1020 yield strength, i couldn't get you.

But from previous experience, the scrutiny judges are pleased with analysis of frame alone and not too much bothered about other details, which is very weird. We didn't want to take any chances so decided to apply the max limits, although the driver will pass out at 8g itself. But your idea is pretty realistic. congrats and thanks man. probably that's what experience does?
Cheers

Suspension Team-2012
GS Racing
MIT India

[shark.ashwa]

Josh,

When I said 290 MPa is too less, I was referring to the material requirements for baseline steel in The FSAE 2012 rules. It lists 360 MPa as the yield strength required if I remember correctly! http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif
Oh and I dont think FSAE cars can handle 8g! http://fsae.com/groupee_common/emoticons/icon_eek.gif
BTW, congrats for what?

Sharath

[josh2417]

Sharath,

Oh i didn't notice that point.

In the rule book it states that the impact attenuator is required to take 20g of deceleration. So we just let the same deceleration.

[shark.ashwa]

Page 23 of 2012 FSAE rules:
"Baseline steel properties used for calculations to be submitted in an SES may not be lower than the following:
Bending and buckling strength calculations:
Young’s Modulus (E) = 200 GPa (29,000 ksi)
Yield Strength (Sy) = 305 MPa (44.2 ksi)
Ultimate Strength (Su) = 365 MPa (52.9 ksi)"

Its 305 instead of 360, damn!
Anyway, I think its always better to be above the minimum required figure! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif
Which team are you from BTW?

[josh2417]

Sharath,
u-turn ??? :P
We are from chennai, Anna University. I hope you guys can teach a little about upright machining and data acq. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[shark.ashwa]

Originally posted by josh2417:
Sharath,
u-turn ??? :P
We are from chennai, Anna University. I hope you guys can teach a little about upright machining and data acq. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Josh,

Always happy to help. P.S. What do you mean by "u-turn???:P"

Regards,
Sharath

[josh2417]

No i meant you said that the factor of safety was pretty high and then now said its better to be above. In between i don't find any rule like that on the supra rule book.

[DougMilliken]

But more importantly i wanted to know if the constraints and load application methods are correct.
Often the best visualization technique is a model that you can bend and twist in your hands. Plastic straws of different diameters can be assembled quickly with hot glue. Because the plastic has a low modulus, it is easy to see where there are areas of high deflection. There is a long history of plastic models in stress analysis--very common before FEA was well developed and fast computers were available. Bring the model or pictures to your design judges--I know that I would be favorably impressed if you brought them to me.

[typeh]

Can i know your chassis weight?

[josh2417]

DougMilliken

Sure will do it to gain better understanding.

typeh

Aiming aroung 60 kgs. Not sure though. USing ms1020 or 1018 mostly.

[typeh]

Sounds too heavy.

[devak03]

hey josh.

were your methods correct. would like to know ur experiences.
participating in Supra SAEINDIA 2014.


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