Compressive strength of aluminum

[jack action]

Two samples will never be alike mainly because of the randomness of the crystal structure defects where impurities, dislocations, and grain boundaries will be slightly different.

So in other words, the inner structure is not consistent inside an aluminum bar therefore the compressive strength will be inconsistent along the length of an aluminum bar?

Metal products have defects just like wood does. The fabrication process is more controlled, so the defects are smaller and more uniform, but they are still there.

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Metals at the microscopic level:

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Introduction to the wonderful world of metallurgy:

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[Astronuc]

Is calibration the same as when we try to drop things on load cell?

Does one mean dropping a mass or load onto the specimen? A drop test is a dynamic test, i.e., relative high load/strain rate, which will affects test results. Strain rate is a factor in both tensile, compressive and shear testing; some alloys are more sensitive than others.

Re: https://www.physicsforums.com/threads/compressive-strength-of-aluminum.1063600/post-7096651

As jack action mentioned, no two specimens will necessarily test identically for the reasons described. There can be small differences in composition (local inhomogeneity compared to bulk/nominal), which can be minimized for products from the same lot. However, one will find some process (thermomechanical processing history) variability, leading to slight variations in microstructure (grain size, grain orientations, dispersed second phase particles, . . . . ), which will contribute to the variability in testing results. In the case of aluminum, storage temperature and time (ageing) of the finished product is also important.

Factors affecting testing variability include differences in load/strain rate, alignment or misalighnment of grips or loading system, variability in specimen and testing temperature, just to name a few.

 

[Joe591]

It might be useful to make both aluminium pieces from the same bar stock. If you want the properties to be nearly the same. If made from the same bar stock then the same heat number will apply to both pieces so the material properties of both pieces will be as close to identical as you could possibly make it. Then it's down to machining tolerances on the indicidual parts.

 

[Juanda]

Buy one bar, then cut two from it.

Notice that the -T6 tells you that it has been treated to make it hard and dimensionally stable. Avoid overheating it during cutting or machining.

"T6 temper 6061 has been treated to provide the maximum precipitation hardening (and therefore maximum yield strength) for a 6061 aluminium alloy."
https://en.wikipedia.org/wiki/6061_aluminium_alloy#6061-T6

If you want them to be very similar I agree with @Baluncore. That should be the easiest way to achieve it. There will still be some variation as others have mentioned but that's always the case.

Also, as others have mentioned as well, without knowing the application for these components it's harder to assess the best approach. Typically, the small variability is not an issue since the strain limit is often far away from the working conditions. If a 1% variability breaks your system then you probably need to change your design in the first place.

Lastly, as a side note, you've talked about compression and taking it at very high values. Again, I don't know the application but, just in case, I advise you to check for buckling.