440-500 lb kept off the gen-1 with aluminum instead steel

[jwmelvin]

Look at the Wikipedia entry for specific modulus, which gives numbers. For equal-weight designs to maximize stiffness of a bending solid beam, Al outperforms steel by about a factor of three. That goes up as you move to a thin-walled hollow beam. For designs in tension loading rather than bending, they perform almost exactly the same.

 

[Bram]

Just and FYI...the switch from Tubular steel frame to an AL or FRP Monocoque in F1, was to comply with al FIA safety regulations.

Bram

 

[Old Guy]

Just and FYI...the switch from Tubular steel frame to an AL or FRP Monocoque in F1, was to comply with al FIA safety regulations.

Bram

I am aware that the FIA has certainly mandated changes to the monocoque structure to increase the driver survivability in the event of bad crashes. However, the monocoque structure first popped up in F1 sometime around 61 - 63 when a partial riveted aluminum tub was used by Lotus for the first time. Space frame cars in F1 were still in use in the late 60s. The FIA may have created regulations that ultimately made the monocoque tub the defacto safety solution (whether or not they specified monocoque construction in the reg); however, monocoque construction and tubular space frame construction co existed in F1 racing so, as far as I can determine, the first implementation of the monocoque construction was a technology / design decision made by Lotus, not a safety change mandated by the FIA. My fuzzy childhood recollection is that the monocoque design had a lot of detractors because of concern about its ability to withstand a crash. My early childhood loyalties were sort of equally divided between Lotus and Cooper.

While we are on trivia items, I think Brabham was the first team to use a composite material in F1 fabrication. It involved wood. Maybe something like the FRP / Wood structures in boats? I don't know the specifics.

 

[Bram]

Very interesting ....I'm always amazed by the the development in F1 over the years. I was not aware of the monocoque construction go way back to the 60's.
Thanks for the information.

Bram

 

[Old Guy]

Look at the Wikipedia entry for specific modulus, which gives numbers. For equal-weight designs to maximize stiffness of a bending solid beam, Al outperforms steel by about a factor of three. That goes up as you move to a thin-walled hollow beam. For designs in tension loading rather than bending, they perform almost exactly the same.

There are different definitions of specific modulus. I take it that you are probably referring to the value calculated as Young's modulus divided by density squared. As you note, that gives an indicator of the relative performance where you have a fixed weight of material and the objective is increased rigidness. That goes back to the point I made in post #2 that the advantage of aluminum over steel is that with the same weight of material you can fabricate a different (more complex or larger) structure that is more rigid. If you read the discussion in the Wikipedia article where they note that if the objective is purely weight reduction, the more appropriate comparison is Young's modulus divided by density. If you look at those numbers, you will see that aluminum's advantage over steel is much less significant. They are as I noted originally, almost the same and within the range of alloys available, could be the same.

It can get a little silly with the comparison of specific modulus numbers. Balsa wood would seem like a much better candidate for construction of the NSX based upon just specific modulus (about 20 times better than aluminum ; however, its modulus of elasticity does kind of suck big time :smile:. The table values for carbon based FRP show why it is such an attractive material. It has a modulus of elasticity that is almost as good as steel and a specific modulus that is 4 - 7 times (depends on which modulus you use) higher than aluminum.

 

[jwmelvin]

There are different definitions of specific modulus. ... if the objective is purely weight reduction, the more appropriate comparison is Young's modulus divided by density. If you look at those numbers, you will see that aluminum's advantage over steel is much less significant.

Yes for sure, that was kind of my point: Aluminum is equivalent to steel in certain applications, such as stiffness in tensile loading for a given weight, and can outperform steel in other applications, such as stiffness in bending loading given a sufficiently large design space. But as you point out with the limitations on wood despite it's high specific modulus numbers, most design imposes geometric constraints and that limits the benefit of materials with higher specific modulus. That's consistent with Acura's explanation for using steel in the A-pillar of the new NSX, because it allowed a thinner structure for a given strength. (And note that we sometimes shift between strength and stiffness in these discussions, despite the distinct nature of those two and the fact that strength of a metal depends on heat treating whereas stiffness does not.)

Old Guy, I agree with everything you have said and was just trying to provide some additional reference material for Patricio. Perhaps I should use this opportunity to thank you for the wealth of helpful and accurate information you have provided on Prime.

FF Drifter, regarding the new NSX, it does not seem accurate to say that a majority of the frame is steel. See this image for reference.

 

[Old Guy]

Old Guy, I agree with everything you have said and was just trying to provide some additional reference material for Patricio. Perhaps I should use this opportunity to thank you for the wealth of helpful and accurate information you have provided on Prime.

Now the pressure is on!! 'Wealth of helpful and accurate information' is not a descriptor that normally gets tossed in my direction. Thank you. I would show this to my wife; but, I fear that she might injure herself with convulsions of laughter!

 

[FF Drifter]

FF Drifter, regarding the new NSX, it does not seem accurate to say that a majority of the frame is steel. See this image for reference.

Thanks for that. I had been under the impression that steel was a much bigger part of the overall structure, especially because some of the marketing materials really hyped up the use of new steel "firsts" in automotive applications.