https://twitter.com/elonmusk/status/1719444510416032022?s=19

 

No other passenger car on Earth is made with a body this rigid.

The who evolution of car body construction has been to make the car sacrificial to the safety of the human occupants, other drivers, and pedestrians.

The car body absorbs impact energy so the humans inside don’t.

So what happens with the Cyber truck in a crash?

Resilience only goes so far.

Very hard materials tend to fail in a brittle manner under load.

So I suspect that this body will go from not being dented to catastrophic failure quickly.

That was one of the problems with the DeLorean stainless steel body.

I know else about this vehicle, I’m just a materials engineer asking questions.

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By J. Kb

10 thoughts on “An engineering question about this video”
  1. Marketing.
    First of all, these days normal cars are plastic. (OK, some kind of fiberglass… but basically plastic). An arrow with any strength to it at all could penetrate. Heck, if I swing a #2 pencil hard enough it would likely go through the outer skin of a lot of todays passenger cars.
    .
    Now… score the arrow along its length so that it will shatter. Leave it with enough strength to make it through the thin skin of a normal car, but not enough to penetrate any form or metal. And, you will get a picture like this.
    .
    So, this is marketing.
    People who get parking lot rash on their cars will want one that is “strong” but they have not idea about things like crumple zones, etc…
    The average person does not want to think about stuff like this, they want cool.

    1. “First of all, these days normal cars are plastic.” Out of curiosity, which cars? I know that Saturn had polymer body panels and most bumper covers are plastic over foam covering some sort of steel crash/impact structure. But both cars (mid-size truck and a run off the mill compact crossover) sitting in my garage and those of most of my associates are stamped steel/aluminum sheet for everything in the exterior except windows, lenses, and grills/bumper covers. Everything is definitely a hell of a lot thinner than in past years in the name of being able to pack more lightweight useless junk into a car or to cut weight for CAFE numbers, so I could definitely put an arrow through the door skin of either of my vehicles.
      .
      Other than that, I’d fully agree that this is all marketing. Elon seems to love to pull these stunts and probably loves this just to try and save face from the launch video. Hell, given a little prep time I could film a similar video with the side panels of my ’87 John Deere garden tractor. Doesn’t mean I want to get in a crash on the damn thing.

  2. 3 series, so soft for stainless. Moderate modulus of elasticity. Depending on temperature, of course. Not likely to be any harder than half hard. More likely quarter hard, or even annealed, for forming reasons.

    Still, significantly harder than plastics or aluminum, and harder than most low alloy steels that are in use.

    I’d have to pull a book to get actual numbers, and I’m betting you have those.

  3. Equally plausible it destroys the car it hits or hitting it much more.

    I experienced similar in a full size blazer. Big near head on crash at 40-50mph. Totaled it the blazer. Did much more damage to newer f150 I hit. No part of my body touched anything other than the seat belt and seat in the crash. Injuries to other people from f150 crumbling around them.

    Rear ended in same blazer twice as well, both times no damage to me but damage to rear ender. Hitch installed but no ball or receiver present.

    Also had a guy pull out in front of me in a corolla, hit him with the same blazer. 10-15 mph hit to his drivers fender. No damage to me.

    Larger, taller, heavier, more rigid vehicle with optimal bumper placement has survived many encounters with bad drivers. I can see the cyber truck doing the same if it is built stout.

  4. BTW — love to get a materials engineer’s take on this:
    .
    https://www.youtube.com/watch?v=CglNRNrMFGM
    .
    Canadian chemist YouTuber followed a research paper to make “densified wood” that the paper theorized could be used to make inexpensive armor. So he spent 3 years off and on working on reproducing their results and eventually came up with a 3-layer piece of plywood that stopped a 9mm round.

  5. Looks like a composite shafted practice arrow, so I don’t necessarily believe that it would do any differently on another car.
    As for “make the car sacrificial”, that’s partly true. More precisely, the passenger compartment is supposed to be quite rigid, while the rest of the car is sacrificial. They call it “crumple zones”. They work particularly well in cars where there isn’t a front engine (Tesla as well as rear-engined cars) because there the entire front can be like an accordeon without dropping a big rigid engine block in the passenger’s lap. You can see substantial extruded longitudinal beams in the Tesla front section; they explicitly serve that purpose of absorbing energy.

    In other words, it is good for an impact test on a door, or any other part of the passenger compartment, to look like this because that part of the car is indeed supposed to resist strongly intrusion into the compartment.

  6. Considering the danger of battery fires, I’m not sure this is unreasonable at all. It seems like a continuation of the already substantial armoring they have under the car body to protect from i.e. road debris. Not sure that its correct, but something to think about.

    Of course it also looks cool, but electric vehicles are different than internal combustion, not all the tricks from one will map neatly onto the other.

    1. Indeed. My S got a retrofit with armor plates on the bottom (titanium, I think they said). Tesla made some videos showing how that deals with substantial debris, like cinderblocks or even an alternator, getting jammed under the body without ill effects.
      In any case, that’s just part of the design rule that the passenger section is very strong and stiff, and the remainder of the car is weaker and intended to absorb energy by collapsing rather than resisting deformation.

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