120mph crash test

[kbui]

Originally Posted by DGthe3

The crumple zones did something ... they crumpled. What more could you ask of them, saving the occupants lives? Oh yeah ... thats what they're there for, isn't it? Oh well. Anyhoo ...

You are right that they slow down the crash event, and that is how they save lives. But how do they slow the crash down? They slow it down by ... absorbing energy. Like a spring. But reverse the efficiency so that instead of wasting a couple percent of the energy as heat & sound while storing the vast majority as potential energy (which then gets released as kinetic energy), they convert the vast majority of the into heat and sound with a minimum being stored & released

Let's see if I can provide more info and keeping it simple at the same time. Most metals are classified as having an elasto-plastic behavior; i.e. with small deformation or strain it acts elastically and under larger deformation or strain it acts more like a plastic. "Elastic" in this sense is referring to its ability to fully recover all of its deformation after the loads are removed. The "plastic" in this sense is the permanent deformations that the material will remains after the loads are removed. This transition between the elastic and plastic is the stress limit or yield stress or strength of the material.

Scooter is correct that the "crumple zone" is not the actual absorber of energy. It's the sheet metal that "absorb" energy. The computed area under the stress-strain curve is the Internal Strain Energy. The progressively crushing of the sheet metals by folding them converts the kinetic energy into this strain energy. Hence the dissipation or reduction of the kinetic energy is what we typically referring to as energy absorption. Hence a more ductile material "absorb" more energies.

DGthe3 is correct that crumple zone saves lives. More importantly, the crumple zone allows the crash engineers to control where the "crushing" occurs to protect the occupants. By designing front and rear structures such that, during a survivable crash, the front or rear structures will crush but the passenger compartment remains in tact. The "control" crushing also allows the engineers to tailor or get a better deceleration pulse or time history of the passenger compartment so that other safety features can join in the protect the occupants.

Hope you all appreciate all the work and effort crash engineers worldwide have been putting in for all of the cars on the road today. These crash analyses are usually a very big factor in the overall design of a vehicle today. With the needs to go lighter and higher MPG and or electric cars, this crash design is only getting more difficult. After what was said and done, hitting a rigid barrier or a similar (or heavier) car head on at 120mph, there is not much anybody can do for you.

[CamaroSkooter]

I guess I should have said that the crumple zones won't be very effective at saving lives when two cars, both traveling at 120mph, hit head on.

Obviously they'll crumple. But them crumpling isn't going to slow down that impact time enough to prevent the life-threatening injuries. Instead of instantaneous death, the passengers will only suffer slightly less than instantaneous death.

I fully understand how the crash safety features work. I just figured I'd try to explain that nothing "absorbs" energy. Energy can be transformed, transferred, or stored, but it can't be created or destroyed. I usually equate the term "absorb" to destroyed, so I guess maybe that's where the difference in opinion lies?

I dunno.

The video is pretty telling regardless of the understanding of the physics behind it.

[JasonK]

that focus looked like a smart car afterwards.

[kbui]

Originally Posted by JasonK

that focus looked like a smart car afterwards.

This is the reason I just can't see myself or any of my family members driving one of the smallest cars on the road.

I can still recall working at the GM tech center in the crash group a long time ago and watch these actual crash tests as well as hi speed videos of these tests for the first time, you get to appreciate how violent these "slow" speed frontal crashes are. It's down right scary. We are only talking about 30 and then 35 mph into a rigid barrier. All the metal pieces (hood, fenders, frame rails, dash...) crumpled as if they were paper. Even at these low speeds, the whole crushing thing was over in less than 300 milliseconds (< half a second).

[DGthe3]

Originally Posted by kbui

This is the reason I just can't see myself or any of my family members driving one of the smallest cars on the road.

I can still recall working at the GM tech center in the crash group a long time ago and watch these actual crash tests as well as hi speed videos of these tests for the first time, you get to appreciate how violent these "slow" speed frontal crashes are. It's down right scary. We are only talking about 30 and then 35 mph into a rigid barrier. All the metal pieces (hood, fenders, frame rails, dash...) crumpled as if they were paper. Even at these low speeds, the whole crushing thing was over in less than 300 milliseconds (< half a second).

Well, I'd consider the Smart to be safe enough in a crash against a similar vehicle (afterall, thats whats required to pass the test). Problem is, nearly every car on the road weighs at least 50% more and a large pickup truck or SUV can weigh 3x as much. Kinda like the difference between a 12 year old getting tackled by another kid his size, or an NFL linebacker.

[kbui]

Originally Posted by DGthe3

Well, I'd consider the Smart to be safe enough in a crash against a similar vehicle (afterall, thats whats required to pass the test). Problem is, nearly every car on the road weighs at least 50% more and a large pickup truck or SUV can weigh 3x as much. Kinda like the difference between a 12 year old getting tackled by another kid his size, or an NFL linebacker.

Exactly ! What makes me laugh is when people trying to tell me that a small car that have a high crash rating and hence it's safer or as safe as a large SUV which might not have as high as a rating .

[CamaroSkooter]

I gaurantee a Hummer H1, with its 3-star* crash rating is safer than that Smart Four-two with its 5-star crash rating

*This is a guess, since I don't think any of the H1's were ever crash-test rated...

[Steve Dallas]

[Gigachip]

wow

[Vengeance Graphix]

Now thats what you call a compact car

Crazy

[Powhusku]

Note to self: Dont drive a ford focus into a wall at 120 mph.

[Steve Dallas]

Originally Posted by Powhusku

Note to self: Dont drive a ford focus into a wall at 120 mph.

I'm pretty sure that applies to all cars (as much as I dislike Fords).

Camaro, as safe as it is, probably wouldn't look much better.

I think Fbodfather needs to find a Camaro they can do this with, and do it at 150 mph, just to show what could happen...

[Vengeance Graphix]

Originally Posted by Steve Dallas

I'm pretty sure that applies to all cars (as much as I dislike Fords).

Camaro, as safe as it is, probably wouldn't look much better.

I think Fbodfather needs to find a Camaro they can do this with, and do it at 150 mph, just to show what could happen...

that would be interesting to see.

[Steve Dallas]

500 mph...