Stresses by High G turn test on chassis in Solidworks ??

[im.freezin]

its not just some random fea....its not jus a random fea...its simpler to wat the guy above did...dont know y the pic doesnt show the direction of force and restrain....i feel its kind of like the car ramming up with a force of 6g's into a waLL...i need ur help to figure out how i can get to know at wat value the chassis crashes...i hav one 2 or three red spots with a deformation of 6 cm max

[PlatinumZealot]

well this is what i got after i tested the chassis with the triangulations....tested it at 6g's...now can u please tell me wat does this test signify...m quite of a newbie n dont know much about this...help!

To make sure the mesh is good: everytime you modify the structure, Go to beams > add all members then go to joints > update
(something like that)

The aim is to see where the material has failed. The design failure stress is the Yield stress of the material divided by Safety factor.

If the colours on the result are over this design stress, you have to make the tubes bigger or modify the layout of the structure.

For instance. If you are using mild steel.. Yield stress is 270 MPa. Divide by the safety factor; example 3.. and the design stress is 90 MPa. That means that no where on the result model should be over 90 Mpa or the frame does not meet your requirements.

Make sure you set the Material of course. Right click on on study (or beams? ) then go to > Material.. you can load Materials from the cosmos Library:
SolidWorks Folder > Cosmos > CWLang > english > Cosmosmaterials.sldmat

Loading that can enable you to use materials like Chrome molybdenum steel and various alloys of aluminum.

Sometimes the material will not fail but the deflection will be very high. You can turn on the deflection results and review the deflections to make sure that all of the corners are within a certain deflection. Like example not more than 4mm deflection etc.

From your Image the stresses are TOO HIGH. Remember yield strength divided by safety factor is the maximum stress.

[PlatinumZealot]

its not just some random fea....its not jus a random fea...its simpler to wat the guy above did...dont know y the pic doesnt show the direction of force and restrain....i feel its kind of like the car ramming up with a force of 6g's into a waLL...i need ur help to figure out how i can get to know at wat value the chassis crashes...i hav one 2 or three red spots with a deformation of 6 cm max

6cm is HUUUGE

When the car hits the wall. There is going to be IPACT. (There are calculations to find the impact force). During impact, because of the sudden deceleration crash forces are multiplied by anything from 1.5 to over 200 depending on the speed of impact (and the static deformation of the object were at slow speed).

To answer your Question. How do you know what force the chassis crashes at?

You have the calculation.. this is with the raw frame.

Actual weight of the car = Mass x gravity .....Newton.
Static deflection of the frame, = The deflection if it was only the weight of the object acting on the crash area. .... meters

Then use this:

Impact Force = Static weight (1 + SQRT(1 + impact velocity^2/(g*static deflection))

Notice that the static deflection is small (stiffer object) and velocity is large the impact Force will skyrocket. Remember this is just as if the Frame crashed into a rigid wall without any crumple zone.

Because, of it's stiffness if raw steel slams into a wall, the impact multiplication factor can be waaay over 100. It doesn't absorb energy plastically until it yields. So the shock is very terrible while the metal is elastic (before the metal actually starts to absorb the energy while crushing).

The equations won't apply to objects that crumple because those object deform non-linearly. They shatter, they break, they tear. Objects like carbon fibre, foam, failed metals etc. You have to test them experimentally; either in real life or in a simulation. These objects are better at absorbing energy and redirecting it into Friction, Kinetic Energy of the shattered parts, tearing of bonds etc.

So Usually there is some type of crumple structure out in front to lessen the impact. That is why I made a crash structure out front of mine.

For example Formula 1 requires the chassis to have a maximum deceleration of 10g's of the first 160mm deformation of the crash structure and the decceleration of the chassis may not exceed 40g's average. All this at 15m/s. The speed is only 15m/s because I think they took into account tyre barriers and run off areas would slow the car. Notice the G ball display during Massa's crash? It showed 5 g's but it was actually waaaay over 5g's. It is easy to go over 200g's without any crash protection.

It took me some trial and error to create a crash box and test it using "Drop test study" until I got the crash deceleration down to ~30g's at 30m/s impact speed. Not great but I was satisfied.

But if you know what the required maximum decelerations are, you can just test the frame without designing a crash structure. Then do the crash structure last or get a recommended one etc.
I don't know how much crash protection those Formula SAE cars have since I am not familiar with them. But check to make sure that 6 g's (or whatever) IS the safety limit. Make sure you don't design it for 6 G's and when you crash you experience 50 g's

I didn't word my explanation good enough because I am sleepy. But i hope you understand.

[Jersey Tom]

What's FEA? And why there are so many squares in im.freezin second design after "triangulation"?

Finite Element Analysis.

Those 'squares' are mesh elements. A beam element mesh like that breaks each tube up into sectors for structural members in bending.

In the end, the answer to this thread original question is to fix the car at the outer wheels, isn't it? So, the car doesn't rotate, does it?

Ehhh, kinda. Depends what you mean by rotate, and reference frame. I really think doing frame FEA for stress analysis is a waste of time in this application. Deflection (and more really springrate distribution along the bulkheads) is more critical.

In any event you wind up getting an inertial torque load on the frame. It's a bitch because it's a distributed load, and part of that load is the geometry of the frame itself.

The importance of this, I mention here

http://fsae1000.blogspot.com/2008/11/im ... idity.html

Though I may or may not have been completely sober at the time.

In any event, triangulation between chassis nodes is important. FEA sectorization happens no matter what.

What's HAZ and the weld pool?

Heat affected zone. When you weld steel, you're heat treating it locally. Strength, hardness, and how brittle the steel is, is a function of that heat treating.

Likewise, when you weld all those joints, you generally don't use a filler metal that's exactly the same. For example, welding 4130 you might use a relatively low carbon ER70-S2 filler. When you melt that into the weld zone you're changing the chemical composition, AND THEN you're heat treating it locally.

Then, even if you go back and normalize your weldment, you've still changed the chemical composition of the weld pool.

That's something I've never seen a FSAE / F.Student team get right. They do FEA on weldments (like this, or an upright, whatever) assuming the mechanical properties are homogenous when they aren't. It works ok for deflection, since you won't change the modulus of the material, maybe even for stress levels, but not for safety factors.

[Sineth_777]

Hi I am designing a chassis in solidworks. Can I please know how the crash testing was done. Also anybody who could tell me a method to do a torsional stiffness test on the chassis?

Thank You
Sineth

[flynfrog]

crash test: Brave driver to be the test dummy, a truck, a steel plate with a hole in it, and a chain. you figure out the rest.

torsion testing can be done with some clamps a good table a couple of bathroom scales a large bar and a dial indicator.