im.freezin wrote: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.
"I was blessed with the ability to understand how cars move," he explains. "You know how in 'The Matrix,' he can see the matrix? When I'm driving, I see the lines."