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Ann R. Thryft
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Blogger
Re: Steel vs. aluminum
Ann R. Thryft   10/9/2012 12:32:39 PM
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Dave, thanks for the feedback. I agree about the greenwashing/PR angle of many corporate sustainability programs. However, it seems to me that doing LCAs is better than not doing them, and having such programs is better than not even paying attention to the subject. The better, more complete LCAs and actually results-producing programs stand out from the crowd. And some actual good can be done along with the PR when the LCA results are used. This is the case in many human endeavors, especially those that require big changes, so I say don't throw the baby out, too.

ChrisP
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Silver
Re: Steel vs. aluminum
ChrisP   10/8/2012 9:06:07 PM
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You are a moderator on Design News and are asking about the modulus of elasticity for steel and aluminum?  Compressive strength is usually relevant to concrete not aluminum. 

 

 

William K.
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Platinum
Wheels, aluminum and steel.
William K.   10/8/2012 8:14:35 PM
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The nice forged aluminum wheels may certainly offer a good weight reduction, which will reduce fuel consumption, and so from that point it will be a benefit to all.   BUT there is a tradoff to be reconed with, which is corrosion. Here in Micchigan where there are many tons of salt dumped on every roadway each winter, I have experienced rim leaks with my aluminum wheels, on every car. Not a tragedy, but certainly an inconvenience, since they must either be repaired, or air added to the tire frequently. I never had that problem with steel wheels. Another challenge is damage to the wheels, I have seen broken aluminum wheels, which must be replaced, while I have hammered bent st=eel wheels back into shape right on the vehicle. Hammering is much faster and cheaper than replacing.

My point being that it is not a one-sided contest. 

My question is how can corrosion of aluminum wheels from concentrated salt water exposure be prevented? Is there a method that is demonstrated to work?

Jerry dycus
User Rank
Gold
Re: Steel vs. aluminum
Jerry dycus   10/8/2012 7:57:27 PM
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   There are a lot of differences between numbers and real life like you mention Dave.  another is steel has to be bigger because of rust over it's life.

   A similar thing happens with CF and medium tech composites where CF looks much stronger but ends up only 5-10% lighter once in place. 

     In looking for lightweight rims for my lightweight EV's because unspunng weigh ratios are much worse than a heavier car, I  measured about 15 each of alum and steel and was surprised to find both were about equal in weight average.My biggest problem so far has been keeping unsprung weight down at a reasonable cost.

     for trcks this lighter weight will pay for itself in either better mileage or higher loads/thus profit so unless too much more costly the Alum is the way to go.  The only downside is the rims get damaged more esily in potholes, etc and maybe getting the tires changed problems.

 

 

Dave Palmer
User Rank
Platinum
Re: Steel vs. aluminum
Dave Palmer   10/8/2012 2:17:12 PM
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@Ann: Environmental issues rarely come up in failure analysis per se, but they do come up in material selection.

On the other hand, I think very few companies would actually base major decisions on a lifecycle analysis.  For most companies, "corporate social responsibility" is more about public relations than anything else.  Acidification, ozone depletion, eutrophication, climate change, etc. may have significant costs to the economy as a whole, but they don't directly impact the company's bottom line.

The only potential benefit is increased sales, if you can convince customers that your product is "greener" than another product.  This was clearly Alcoa's intent in funding this study.

Large companies may be doing lifecycle analysis (for instance, Pepsico recently completed a fairly comprehensive analysis of its packaging, using tools developed at Columbia University), but it's not clear that they actually using it to make decisions yet.

Personally, I think elimination of waste, conservation of natural resources, and minimization of environmental harm, are important goals.  Unfortunately, I think few companies are really paying much more than lip service to these goals.   

Ann R. Thryft
User Rank
Blogger
Re: Steel vs. aluminum
Ann R. Thryft   10/8/2012 12:24:03 PM
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Thanks for your comments, Dave, that's a good point about the difference between forging versus sheet metal production. That also made me wonder--in your failure analysis work, to what extent do you encounter LCA issues, facts, details, studies, etc.? Is any of that data relevant to failures?

GuidoBee
User Rank
Iron
Re: Strength isnt Everything
GuidoBee   10/8/2012 10:46:22 AM
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Some years ago there was a move toward a "super tire" that was mounted on a different wheel, which was aluminum (Alcoa, I believe).  One super tire combination would replace two wheels/tires on a trailer with the one (per side per axel).  I have not seem many of them on the road (I'm in NM), but they were touted to be improvements over the (then) current technology.  One drawback acknowledged at the time was that they would cost $1200 per wheel; also, the normal truck tire repair guy could not service them routinely. 

Hope there is some real motion toward improved technologies.  Reduced weight should be safer as well, as any reduction in un-sprung weight is a good thing (though it's probably a reach to expect much improvements in handling on a truck/trailer combination).  PSI loading on the pavement may not benefit from a reduced footprint on the super tire, either.  Anyway, it's a good idea, and the benefits to the environment are always a plus.

Toaster
User Rank
Silver
Strength isnt Everything
Toaster   10/8/2012 10:02:23 AM
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Agreed that the design of the Aluminum wheel is a major factor in creating a wheel that is stronger (and lighter) than steel. But... I would like to see the FEA on the aluminum wheel under stress. Steel Wheels are flexible, and therfore are forgiving under load. Will the aluminum wheel be as flexible? At all temperatures?  

Mydesign
User Rank
Platinum
Any need to replace Steel wheels by Aluminium wheels?
Mydesign   10/8/2012 12:36:32 AM
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1 saves
Ann, are you able to foreseen any significant advantage in replacing the steel wheel by Aluminum wheels. I don't think any advantages because we cannot reduce the number of wheels in any heavy weight carriers or trailers. The number of wheels is proportional to the curb weight and length of base platform. Moreover, some road transportation laws restricts any change in length of these base platform and height of the vehicle.

Dave Palmer
User Rank
Platinum
Re: Steel vs. aluminum
Dave Palmer   10/5/2012 7:45:33 PM
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@Charles Murray: The elastic modulus of aluminum is about 1/3 that of steel (10,000 ksi vs. 29,000 ksi), and the tensile strength of a typical alloy used for aluminum wheels is about 1/2 that of a typical high-strength steel sheet used for wheels (45 ksi vs. 90 ksi).

Based on that, it would be easy to conclude that steel wheels should be stronger than aluminum wheels.  But this would be a mistake.

If steel is twice as strong as aluminum, then why are aluminum wheels stronger than steel wheels?

Aluminum wheels are stronger due to their design, not their mechanical properties.  Compare the section thickness of a forged aluminum wheel to a typical steel wheel.  The steel wheel is made from relatively thin sheet metal.  The aluminum wheel is much thicker.

If you made them both the same thickness, the steel would be stronger, obviously. But if you made a steel wheel the same thickness as a forged aluminum wheel, it would weigh about 3x as much (7.8 g/cm² vs. 2.7 g/cm²).  Nobody would want to put this heavy of a wheel on a truck.

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