Direct Shear vs. Moment Load 1

[kklinger]

I have a pinned joint where one part can rotate about a pin fixed on one end (cantilever). The pin is 1" diameter and the gap between parts is approx. .1". I know that if there was zero gap between the two parts, I could treat the loading on the pin as direct shear (similar to a bolted connection in shear). Does anybody know how big the gap would have to be so that the loading would change from a direct shear loading to a cantilever (moment) load.

TIA,

Kirk

 

[rb1957]

i think the reason for considering the zero-gap as direct shear load is that the parts are considered to be locked together, that relative rotation is prevented.

once there is a gap this rotation constraint is released, and the pin bends (albeit with a fixed end, like a cantilever).

i guess the conservative ("lazy") approach would be to consider the pin to be a beam, and if it works great. if you need to "sharpen the pencil", then you might need to look into contact between the pieces, which would prevent relative rotation.

 

[zcp]

The loading does not change. The ratio of predominately shear stress to predominately bending stress is what will change. Write your equation for shear stress in the pin. Then write the equation for bending stress with your gap distance as the variable. Increase this distance until the bending stress becomes large enough to neglect the shear stress. That is your answer.......then try for various pin diameters to create your own 'rule of thumb'.

ZCP

http://www.phoenix-engineer.com

 

[mmart]

Raork's chapter 13 has an article and set of equations for calculating the stresses on a cylinder within a clylinder which i think can apply here.