Since aluminum structures are stronger than steel ditto of the same weight, does anybody know why Model S has steel parts in the body? I am thinking of the b pillar inserts for example.
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SteveS0353
Member
Yes, but steel structures are stronger than aluminum of the same volume, although heavier. I suspect the selection of steel for some components is a volume / strength requirement, irrespective of weight.
Agreed, but how can there be that little space in the b pillar? It is surely mostly empty. Or can it be an afterthought to make the b pillar stronger than its initial design and too late to change the tools for the aluminum parts? or have something to do with its bond to the rocker panel? Perhaps there is some volume conflict somewhere there?
Another example then: Bumpers. There is a lot of empty space in the bumpers. So why are they made of steel?
One of the least stressed parts of the suspension, namely the upper front A arms are steel too. Very surprising. Even the old A6 had upper all aluminum arms, and that was a steel car
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SteveS0353
Member
Metals exhibit different characteristics when deformed. For example, aluminum is more malleable than steel, but aluminum is subject to fatigue failure more readily than steel. Design engineers select materials considering many factors, and the "best" material is very much application dependent.
Ok but if this boron steel is stronger than aluminum for its weight, why isn't the whole car made of it?
The upper A-arms don't need to be very strong relatively speaking, but they are steel.
The upper A-arms don't need to be very strong relatively speaking, but they are steel.
Here is an example that I know about with bicycles. A lot of it has to do with the geometry of the parts you are dealing with.
Aluminum bikes are lighter than steel bikes (in general). This is because Aluminum can make larger diameter tubes, while still having sufficient thickness as to not dent easily. Due to the fact larger diameter tubes are stiffer, and have more weld area they are stronger than thinner tubes. You could make a steel bike frame with the same diameter tubes, with the same mass of material. But the tubes would be made out of super-thin foil. Allowing the walls to buckle easily. This is all due to the geometry of the tubes.
A lot of these types of considerations, along with cost, get factored into manufacturing. And blanket statements like aluminum is stronger than steel is a generalization and doesn't hold for many engineering cases.
As for bumpers they are required to absorb energy. Steel is more mailable than aluminum (in general), and thus easier to get to bend(deform), but not break. So it is a very appropriate material for a bumper.
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Not to mention all sorts of fatigue/corrosion/hardness/fabrication concerns that also may come into play.
