7075-T6 Failure
7075-T6 Failure
(OP)
I am using some machined from solid aluminum flex shaft couplings made from 7075-T6 aluminum. Sometimes when the allen head clamp screws are over tightend, the coupling breaks at the screw head. This does not surprise me in that the screw shoulder is pulling right on the stress riser at the bottom of the screw head pocket and that's right where it snaps. The break shows no yield before breaking; the break surface looks like brittle fracture like a piece of chalk would look like if you snapped it. Is this typical for 7075-T6?





RE: 7075-T6 Failure
What size is cross section that is failing?
It is not unusual not to see evidence of ductility in an aluminum fracture
RE: 7075-T6 Failure
1) Can you use a bullnose end mill to create the counter-bore (pocket) to minimize the stress riser?
2) If you really must stick with Aluminum for lightness, then maybe you can thicken the section underneath the bolt head to reduce nominal stress.
RE: 7075-T6 Failure
RE: 7075-T6 Failure
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: 7075-T6 Failure
http://renbrandt.com/onep_details.html
My question is for information only, we are switching to a different coupling (primarilly for a higher torque rating, Renbrandt makes high quality couplings).
But it's the appearance of the fracture that got my attention. It looks like what I would expect to see in an aluminum casting.
RE: 7075-T6 Failure
Here is similar type coupling that we used with very good success that you may want to look at. The only time they broke was when we overwound them by various means.
http://www.heli-cal.com/
RE: 7075-T6 Failure
You said "...we are switching to a different coupling (primarilly for a higher torque rating..."
Does this mean that it was a geometry problem -- just not big enough or is it different material like alloy steel or...?
RE: 7075-T6 Failure