Shear out in acrylic

[mellejgr]

Hi all,
I am designing a small experiment where I have a pinned joint near the edge of a sheet of PMMA.

I considered the formula e=F/(2*S*t), where e is the minimum distance from the centre of the hole to the edge of the plate, F the applied load, S the shear strength, and t the thickness of the sheet.

I am concerned that this analysis may not be sufficient to prevent shear-out during the loading. Does anyone have experience with this type of loading in soft materials?

Kind regards,
Melle

 

[Compositepro]

Plastics are terrible in that type of loading and will either creep or stress-crack if the load is continuous.

 

[TugboatEng]

Can you install a bushing to reinforce the hole?

https://www.clickbond.com/product-detail/bushings/through-hole-spacer-insert-bushing

 

[mellejgr]

I like the idea of the bushing, am I correct in thinking that the compression of both sides of the bushing help distribute the load, and thus reduce the local shearing stress on the plastic?

 

[TugboatEng]

These are actually adhesive mount. The system uses an acrylic adhesive and the red rubber plug thing squeezes the bushing together while the adhesive cures. It is discarded later.

 

[SwinnyGG]

The bushing will alleviate the point contact at the bottom of the hole. That's limit creep a little, but it'll still happen to some degree if the loads are high. The bushing will also distribute the same load over a larger area which again will help. But don't expect miracles.