How to determine max allowable strain hardening for 2024-T3 Al? 1

[LocutusScientific]

I am considering a bending operation for a thick (3/4") aluminum plate. It looks like the plate will undergo approximately 3% strain on the convex side of the bend. How can I determine what an acceptable amount of strain is that will not damage the part, but only work harden it? To me this maximum allowable strain during the bending operation should be based on the published percent elongation for the material, but I haven't been able to find any references for this.

 

[WKTaylor]

What is the required bend radius and what is the bend-angle?

This is why an extruded angle of the exact thickness/angle/lengths/etc to meet requirements is often better than formed thick parts. Next best is hog-out from Bar stock,... then AHT to -T81 [which is far-less SCC/EXCO prone than -T3 or -T4].

Regards, Wil Taylor
o Trust - But Verify!
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[EdStainless]

Of HT the extrusion to "0" and then form, and age afterwards.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[LocutusScientific]

Thanks for the advice. It is bent to 25 degrees with a 12.5" bend radius. This is a bend at the tip of a 100" long fan blade.

 

[MagBen]

How did you get/calculate strain? fixing the bend angle, the bend strain is proportional to the thickness of the plate, and inversely proportional to the bend radius. nevertheless assuming 3% does not count "springback", so you bend was beyond the yield strength, and the material mechanical characteristics got changed (e.g some degree of hardening). However, the elongation of this material is about 20%, it is unlikely 3% strain will "damage" (how do you define damage?) the part. A general easy method is careful check the convex port for any cracking, orange peel, any abnormal. you could increase bend angle until cracking occurs to get a sense how easy is the material get "damaged". You could also examine the micros for micro cracks etc. if you donot trust human eyes.

 

[realtime2]

Percent elongation of a tensile test sample may not be best source. One needs a "True" stress-strain curve.
i.e. when a material reaches the Ultimate tensile stress, localized "necking" begins and invalidates the
true stress- true strain values after the ultimate is reached. Elongation includes the extensometer deformation
past the strain at ultimate. In a bending case the high strained surfaces are constrained by the lower strained
material below the surface, so necking probably won't be seen, thus the true stress-strain curves should
be ok. There is one available online for 2023-T3.