On Jun 15, 7:15 am, GeorgeB wrote:
On Wed, 13 Jun 2007 19:30:04 GMT, Orval Fairbairn

wrote:
Of course, 2024-T3 doesn't snap as easily as 6061-T6! It is the "T
number" that determines brittleness (and stiffness).

Orval, stiffness is the same for the same alloy, and substantially the
same for all aluminum alloys, independent of heat treatment
conditions. "T-number" has nothing to do with stiffness.

No, it isn't! Try to bend some .025 6061-T3 and then some 6061-T6. You
will find the T2 bends more easily.

If you want to use incorrect terminology, that is fine. Stiffness has
nothing to do with plastic deformation. If you take the same size
piece of 5052, 6061, 2024, or 7075 and load them the same BEFORE
plastic deformation, you will see virtually no (less than 10%)
difference in deflection vs load.

A socket head capscrew, US, is about 220,000 psi yield strength. A
cheap hex head bolt is about 30,000p psi yield strength. For the same
load, before plastic (inelastic as you use) deformation, both will
stretch the same and recover the same.

Yield strengths (and tensile, but yield is the one we USUALLY care
about) vary among alloys and heat treatments.

That is why "T-number" controls stiffness, since bending is the result
of inelastic deformation. It takes more torque to bend a piece of T6 vs
T3 of the same alloy and thickness.

Stiffness and INelastic (usually referred to as "plastic") deformation
have less in common than your and my knowledge of material science.

2024 is about 5% "stiffer" than 6061. 2024-T4 yields about 40% more
in tension than 6061-T6 before breaking.

Yes.

2024-T0 is 5% stiffer than 6061-T6. 6061-T6 is 25% stronger than
2024-T0.

You're not confusing 2024T4 with 2024T0, I hope?

Dan