Bearing stress on a rectangular shape on shaft coupling

[eliam]

Hello,
I have a shaft under torque,
this shaft is coupled by a rectangular connection to transmit the rotation.
Witch is the maximum bearing stress on the surface in contact in the coupling?

we have:
a= long side
b= short side
L= lenght of connection

I'm drawing a sample for better understanding
Thank you

 

[electricpete]

Fwiw I don't think I can help but that never stopped me from providing thoughts before!

I don't see a drawing yet. How does this clamp to or attach to the cylindrical shaft? Or if there is a transition that will need explanation.

Is there a flexible element in the coupling? What speed will it operate at? It strikes me that square cross-section coupling has a resistance to bending in a given stationary direction which will vary as the coupling rotates.... resulting in oscillating reaction loads and vibration.

 

[geesaman.d]

Are you (the OP) describing a rectangular-section key?

 

[eliam]

Here, a picture of square connection:

https://drive.google.com/file/d/1UVrMBpH8odVEkQmY8NsTgkfr46Sh0Npq/view?usp=sharing

 

[dvd]

There is a big stress concentration at the very small radius where the square section joins the circular section. This is most likely your failure point.

 

[Tmoose]

On six-sided drives ( like a wrench on a hex head cap screw) at times the contact at the corners has received a great deal of attention. Your square drive may have similar loading.
In addition to the transition mentioned by dvd.

example "Flank drive" as probably originated by Snap-On.

https://photos.smugmug.com/MotoIQ/Tech/Sarah-QA/i-46QhDQf/0/29ea51a5/S/flank drive-S.jpg

https://www.transtime-tools.com/data_pics/0001 (36).jpg

https://www.datamp.org/patents/displayPatent.php?pn=3273430&id=28255

As always, if the load is low or the service life is short, you can get away with practically anything.