Deterioration of Joint Capability for Low Edge Distance Hole 2

[Ryan_aero]

Hey all,

Does anyone have a literature source discussing how rapidly composite (carbon fiber) joint capability deteriorates as a function of edge distance? I understand anything less than 2.5D runs the risk of undesirable failure modes occurring. I'm being asked to look at joint with e/D = 1.75 and the joint cannot be modified. I understand the only way to get good values for this is to test, but I'm interested in understanding "ballpark" knockdowns for a low edge distance hole such as this.

If you don't have a literate source, I'd still be interested to hear what others think a conservative knockdown would be for a low edge distance hole such as this (i.e. divide the bearing allowable by 2,4, etc.)

Thanks,
Ryan

 

[jotunn]

You've hit the standard caveats...test...change in failure mode (i.e. shear-out)...etc.

Those stipulations aside, for a "ballpark understanding": CMH-17, Volume 1, Chapter 2 (section 2.3.5.5.4 in Rev. G) has a decent discussion on shear-out strength vs. "bearing" strength (bearing in quotes since that's not the actual mode of failure) as a function of e/D (data from 1.5, 1.9, and 2.5 shown).

A fair number of corporate stress manuals also have stuff like this...if you're at a company that has such a thing...

 

[SWComposites]

Here is a conservative estimate:
If protruding head fastener, draw straight line from bearing strength at e/d = 2.5 to 0.0 bearing strength at e/d = 0.5
If countersink fastener, draw straight line from bearing strength at e/d = 2.5 to 0.0 bearing strength at e/d = 1.0
Find bearing strength at e/d = 1.75 on the straight line.

 

[Ryan_aero]

jotunn/SWComposites,

Thank you - that's exactly the info I needed.