Insert bending test

[dcascap]

Hi,

I wanted to know if there is any bending test for sandwich CFRP/honeycomb structure insert.
Basically I have an insert on the middle of a CFRP sandwich panel which is introducing quite a big bending moment to the panel itself due to the boundary conditions of the structure.
I know that for pull-out, shear, and torque there are quite some tests, but I wanted to know if there is any test to obtain bending moment allowable in a direction.
From my perspective, if the insert is done in a way that it has very little tolerance with the face sheets probably the moment will be carried by the faces in compression, instead by the core in shear making it a bit stronger but I would prefer to test it...


Thanks in advance!

 

[SWComposites]

I am not aware of any such standard test. You will likely need to design a test setup.

What is the structural configuration that is introducing a large moment at a single insert? Sounds like a redesign is needed.

 

[dcascap]

yeah that is what I thought... I can't redesign but I think for now I'll need to figure out if the moment is real or if is just because of the way I modelled it.

Thanks for your answer!

 

[SWComposites]

if you have modelled it with the typical single node connection at the fastener, connected with spring/cbush/bar element, which ignores contact surface and clampup effects, then the moment is likely incorrect (way too high).

 

[dcascap]

The model is a bit more complicated than that haha but of course FEM connections tend to rely in a lot of assumptions to simplify the model itself.
Thanks for your help, I appreciate it!

 

[Compositepro]

This is what hardpoints in sandwich structure are for. You can remove the honeycomb around the insert and replace with putty. Or you use rigid plates on one or both sides of the structure so there is little bending moment on the sandwich panel insert.