cantilever load test

[greencircle]

Hi Guys,

I have a aluminum cantilever arm that I want to load test for 400 lbs weight. Wanted to hang this weight on the end of the arm to see if this can take the load.
Since I have difficulty with finding the needed weights. Can I instead use a cylinder that can push the end of the arm upwards for 400 lb-force.

Are these to same?

Thanks
GC

Thanks,
GC

 

[Jboggs]

Force is force, regardless of where it comes from.
However, when you say "load test", that phrase can have a very specific meaning including the use of a certified shop with certified calibrated weights, approved setups, specified overload factors, official labels, detailed procedures governed by codes in some jurisdictions, etc. Saying a design is "strong enough" is one thing, and it means different things to different people, but saying it is certified for a certain load is another matter altogether.

 

[EdStainless]

Or you use a leaver arrangement to load it, like they do when they test scales. Then you can use a couple of hundred pounds to apply the needed end load.

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P.E. Metallurgy, Plymouth Tube

 

[SwinnyGG]

Hanging weight and vertical force may not be EXACTLY the same- depending on the length and section of the beam, gravity may or may not be significant.

 

[Sparweb]

Aluminum beams are likely to have large deflections before they fail. Permanently deforming a beam (plastic deformation) implies that you are on the non-linear part of the stress-strain curve.
Make sure to recognize this in any stress analysis that follows such a test.

Compression is NOT equal to tension, except for light loads that don't get out of the perfectly elastic stress range. Beam failures usually start on the compression side, in particular by local crushing or buckling of parts of the cross-section shape. If you reverse the load direction then the stresses reverse - which is valid only if the beam is symmetrical. Also make sure to identify the direction of the real load as the beam deforms. It may remain aligned with the tip, or it may remain in the same direction. When large deflections are at play, the angle of your test rig can grow to unrealistic directions, depending on where you apply the load, and what the real load condition looks like.

If you set this up yourself, think through the safety aspects of conducting the test - for you and all other people involved.


STF

 

[gruntguru]

Using a cylinder to push upwards should be safer than weights if the beam fails. Upwards is equivalent to downwards provided the beam is symmetrical about a horizontal plane.

je suis charlie

 

[greencircle]

I agree gruntguru.

Yes, I am doing this to meet a code's requirement. Load test 4 times the final product's weight for 1 hr and see if the lever arm sustain visible distortion and damages.

Unfortunately, can't keep the cylinder pushing 400 lb-force constantly for an hour. compressed air leaking issues. the load gradually reduces. I may have to go weights.

Thanks for all the input guys.



Thanks,
GC

 

[EdStainless]

The other way is to use an anchor in the floor, a chain hoist, and a load cell.
Even one of the old fashioned mechanical cells with a "U" frame and a dial indicator would work.

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P.E. Metallurgy, Plymouth Tube

 

[rb1957]

400 lbs = 2 people ... do you have two healthy (or unhealthy) sized individuals around ? simple enough test ...

another day in paradise, or is paradise one day closer ?

 

[rb1957]

what sort of safety factor do you need ? or is 400 lbs the factored load ??

another day in paradise, or is paradise one day closer ?

 

[Jboggs]

80 psi on a 2.5" bore cylinder = 400 lb. You don't have a compressor that can hold 80 psi for one hour? Rent one.