Torque-Limiter Safety Pin 1

[dougouk]

Hi all, not quite sure which sub-category I should post this to,

I need help/tips on looking for a glass pin that will break when it reaches a certain torque.

So what I have in my design is, two shafts that are connected by a coupler, and the coupler has a glass pin through it, which ultimately transfers the rotation from one shaft A to shaft B. The whole design is much more bigger, but to put it short, there's going to be friction on shaft A. Torque. It's on shaft B too, since the coupler+pin is transferring the rotational energy. And if there's too much, I want the glass pin to break, which will stop the transfer of rotation onto shaft B.

The problem is, I need to figure out what type/diameter of glass will break at certain torques. Can anybody kindly give me a lead on this?

Thanks guys,

 

[arbreen]

The theoretical torque required to break a shear pin will be:
A*S*R*2
where
A = glass rod cross-sectional area
S = shear strength of your particular glass
R = distance from shaft axis to the places where the pin would break
2 assuming your pin will break in two places at once (double shear)

I understand glass strength is affected greatly by material imperfections, so your pin may fail at a much lower torque than predicted by this simple formula. Creating your own imperfection (grooves where you want the pin to fail) can make a shear pin more predictable and consistent. At any rate, you will need to test your pin to have any confidence in your numbers with glass. If you can use a steel pin instead, you will probably have better results all around.

 

[dougouk]

Do you have the source?

Can you kindly tell me the units of Shear strength (is it MPa?)

By breaking in two places at once, is that always the case? Wouldn't one side break first, and the other side usually stays? Even if so, should I still use the "2" in the equation?