What would be the approximate sheer strength of 3/8 in. and 1/2 in. aluminum rod

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JimPghPA

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I have an engineering design question regarding sheer strength ratings and deflection.

I am looking at the design of a platform with collapsible legs. The side of the platform will have 4 collapsible legs (on the corners) with 4 axles. Two of the legs will be attached so the closest side is 1/16 of an inch form the platform and all 4 legs are 1 inch wide. The other two legs will be 1 and 1/8 inch from the platform at the closest side, and again are 1 inch wide. The 4 axles can mount into holes a couple of inches deep in the platform. And they can go all the way through the 1 inch wide legs. If I use something like (6061 aluminum or 6063 aluminum) solid round rods for the axles, would they handle the load? I know that 6063 is weaker than 6061, but it is oxidizes less over time.

So, what is the sheer sheer limit of 1/2 aluminum rod?

And would the deflection of the 1/2 aluminum rod be anything significant with the worst case of the two legs that start 1 and 1/8 away from the platform?

Also I am looking at using some pins to limit rotation and wonder what the sheer strength of 3/8 round aluminum solid rod is?

I looked on the internet, but unfortunately when you enter 1/2 inch you get results for 1 and 1/2 inch axles.

Thanks for any responses.
 
What kind of aluminum? Pure aluminum is way too soft. Alloys with small amounts of impurities will be much stronger. A typical airliner fuselage is proportionally thinner than an aluminum can, but much stronger and stiffer as a result of using alloys.

There are tons of variables too, including whether it's cold forged. Cold forging strain hardens the metal and make it less likely to bend. It wasn't aluminum, but in a college introductory materials science class we had a class demonstration. The professor had a solid rod of pure, annealed copper. He found one of the smallest women in the crowd and asked her to bend it. She did so and it was frankly rather easy - almost like the Wonder Woman intro from the 70s. Then he got it back and found a guy in the class with the biggest arms and asked if he could try to straighten it out. He kept trying and couldn't do it. At a certain point it got hard that it would have been near impossible for a person to bend it back. And whatever might bend it back would possibly result in it fracturing.
 
“Engineering is the art of modelling materials we do not wholly understand, into shapes we cannot precisely analyze so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance.”- Dr. AR Dykes
 
y_p_w said:
What kind of aluminum? Pure aluminum is way too soft. Alloys with small amounts of impurities will be much stronger. A typical airliner fuselage is proportionally thinner than an aluminum can, but much stronger and stiffer as a result of using alloys.

There are tons of variables too, including whether it's cold forged. Cold forging strain hardens the metal and make it less likely to bend. It wasn't aluminum, but in a college introductory materials science class we had a class demonstration. The professor had a solid rod of pure, annealed copper. He found one of the smallest women in the crowd and asked her to bend it. She did so and it was frankly rather easy - almost like the Wonder Woman intro from the 70s. Then he got it back and found a guy in the class with the biggest arms and asked if he could try to straighten it out. He kept trying and couldn't do it. At a certain point it got hard that it would have been near impossible for a person to bend it back. And whatever might bend it back would possibly result in it fracturing.
Click to expand...

Probably just the common alloys every day used like 6061 in T6 temper, or common 6063 such as normally found on sites like metalsonline.com
 
JimPghPA said:
Probably just the common alloys every day used like 6061 in T6 temper, or common 6063 such as normally found on sites like metalsonline.com
Click to expand...
I used to ride bicycles and 6061 was one of the more common alloys used. I'm not sure about a rod. I'm more familiar with tubes. From my bicycles days, I remember reading about the design philosophy of some aluminum frame makers. Vitus had this really thin aluminum tube glued into aluminum lugs. I never rode on one, but I understood it to be rather soft where it flexed a lot. Another design philosophy was to use a wider tube made of thinner material. That would actually be much stiffer and just as strong. That's what Cannondale was concentrating on at the time.

I have nothing really to add (not a mechanical engineer or a materials guy), but I was thinking tubing might actually be a better choice than solid rods if you can manage.
 
I am thinking that even though aluminum is a much weaker material than steel, a 1/2 inch diameter solid shaft is going to be able to withstand a lot of sheer force and with such a short leverage of 1.125 inches at the worst case, I do not expect to see any significant deflection. It would just be nice to get some ballpark figures of what would be a significant force for such an axle, and comforting to know that the maximum load would be only a fraction of what it could handle.
 
So, I didn't understand your description, but the internet says the shear strength of 6061-T6 is 30,000 PSI. The cross sectional area of a 1/2" diameter rod is 0.785 sq.in., so the shear strength would be 23,561lb. The 3/8" rod is 0.44 sq.in, so 13,253 lbs.
 
EdwardC, thank you. I kin-of thought that 1/2 was over-kill but that is OK. I was going for over-kill, but in this case it is way over-kill, but still that is OK.

Thank you.
 
Just friendly advice FWIW, going about this kinda backwards if this is expected to handle really stressful loading.

The published specs in a nutshell are starting points because there are innumerable things that change it and those specs are against standard tests for linear comparisons and have no bearing ( or very little) on actual finished working loads of a given design.

You need the dimensioned design ( need to know stress points, risers, expected forces for the fatigue calculations) and whatever working loads so the needs of the design can be calculated- then select materials. ( the dimensions of the materials selected add a whole new set of changes to the baseline calculations and that's without varying alloying recipes and ancillary treatments or even fastening methods)

Example, you cant really assess a deflection ( bend moment) without a span, where its supported and how much force it is seeing ( and from what direction, frequency and amplitude)- anyone who may think differently has no idea of the science behind this type of calculation. ( theres a reason that SE is a separate certification for a PE) I don't believe this is that complicated but if its a concern we would really need a dimensioned drawing to assess or either a working load diagram/profile the platform would have to withstand to get a really good and accurate load assessment and material selection.
 
Wow. It's been nearly a year and no one has corrected this post?

So, I didn't understand your description, but the internet says the shear strength of 6061-T6 is 30,000 PSI. The cross sectional area of a 1/2" diameter rod is 0.785 sq.in., so the shear strength would be 23,561lb. The 3/8" rod is 0.44 sq.in, so 13,253 lbs.

The cross section of a 1/2" rode is not .785 in^2.

The cross section is 1/2 the radius, squared times pi.

1/2" rod is 1/4" radius. 1/4" radius squared is 1/16" or .0625
time pi is .196 in^2.

Times 30K psi shear strength is 5,890 pounds.

Not 23K#s.

BIG difference.

Same issue with the 3/8" rod. Divide the answer given for it by 4 to get the right answer.
 
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