Its said that cars are “weaker” because they’re now made from a softer material proper to receive impact, thus providing safety to the driver. How will safety work with cybertruck’s 30x ‘ultrahard’ stainless steel when crashing?
In: Engineering
When a car hits something, it’s coming to a very sudden stop and all that energy has to go somewhere. In older vehicles made mostly from steel, that energy usually ended up going into the passengers and cargo, which would cause serious injury. Gradually, cars began to be designed to crumple on impact instead, so the car would absorb most of the energy and the passengers would be less likely to get seriously hurt.
I don’t know how the Cybertruck is constructed but crumpling is only one of the possible ways to get the car to absorb the impact energy. It is possible to use a sturdier material while still achieving the same goal through different physics.
Hard is not the same as tough is not the same as strong.
Cybertruck’s stainless steel body panels are hard; they’re probably also tough, although that’s usually not very relevant for body panels. They’re not any stronger than they need to be though (since that’s what drives weight), so their crash behavior shouldn’t be meaingingfully different.
Hard = how easy it is to scratch. This is obviously really relevant for vehicle body panels, we want them to stay looking nice, harder materials are harder to scratch and stay good looking for longer.
Tough = how easy it is for a crack to grow. Body panels don’t usually crack so this isn’t a big deal. It’s a huge deal for fatigue-critical structure (stuff that goes through a lot of stress cycles) but that’s also not usually a big deal for body panels, they’re mostly decorative and not carrying nearly as much load as the chassis.
Strong = how much stress it can carry without yielding (permanent deformation). Cybertruck doesn’t need to be 30x stronger…it might be 1 or 2x stronger because of the extra battery weight, but nowhere near 30x. That would just be wasted weight, which drives down range and drives up costs, so there’s no reason to do that.
There is probably a difference between the stuff and design used as the energy absorbent crash structure versus the internal frame that has to hold the load of the vehicle. You can absolutely make crash absorbent structures even out of very “hard” material – it is more about the shape than the materials used. Nonetheless, it would seem intelligent to only use the very strong and expensive material for load bearing internal structures and not the “outer” part of the vehicle.
For the cybertruck, the intent is you can throw a brick at it and not dent it. However the force of a brick is nothing to the overall car, it’s not going to hurt the driver if it hits the hood. Meanwhile driving into a brick wall will hurt the driver, it will dent the body panels, and it compress the crumble zones. This is because they just have steel plates on top of a frame with all the usual safety things and it doesn’t rely on the body panels
For safety.
An aside – if you get in a crash involving a semi truck and you aren’t inside, you are dead. It doesn’t matter how crumply the truck is. It is so massive that it isn’t going to stop.
The purpose of the crumple zones are to slowly absorb the energy of a crash so that the passengers slow down over a greater amount of time. When dealing with a semi, the semi has such a large mass that there is no chance of slowing it down. If you crash into it, you might as well be crashing into a wall.
I think you’re looking too far into this. Take one look at the cybertruck and tell me that it will ever actually be sold. Tell me that you will see one on the road. No, it’s not real. Whether or not the “30x(???) ultrahard stainless steel” will interfere with crumpling action in case of a crash is immaterial because there won’t be cybertrucks around to crash into anything. It will never come out. I refuse to believe that something so stupid will ever exist.
Rigid is dangerous, basically what you are interested in is a deceleration force (basically g force) if you stop from 30 MPH in 1/1000th of a second your body is subjected to a huge deceleration force and it can kill you if you have the same impact over 1 second then you are likely to survive. The crumple zone of the other vehicle really isn’t what is saving your life here, the only extra risk with the crumple zone is if bits of the vehicle are pushed into the passenger space.
Contrary to popular belief, modern cars are WAY safer than decades-old cars. Modern cars have stronger frames and stronger internal occupant protection cages, plus crumple zones that give way and safely absorb energy upon impact. Older cars have heavier external sheet metal, but their occupant compartments are far more easily compromised in the event of a collision and they are far less effective at safely dissipating energy bc they lack crumple zones.
For anecdotal proof, ask an extrication specialist (think jaws of life) who regularly has to cut into the occupant compartments of crashed vehicles to remove injured or dead people. They’ll tell you that cutting into older cars is way easier bc the steel is softer.
For a crash test, see https://youtu.be/TikJC0x65X0.
Didn’t Elon Musk say it was almost bulletproof. To be like that it would need to be both tough and also hard. There’s probably something holding the plates together that crumples instead.
The passenger compartment on today’s cars is stronger than past cars. There is a ton of crash test data to support this. Body panels are weaker but their function is cosmetic and for aerodynamics, they don’t contribute to much to crash resistance.
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