Back to Basics FBD 3

[galaxy212]

Hi All,

I have a really simple FBD problem though its been a while since I have had to do them so I was wondering if somebody would be so kind as to check my logic. FBD attached. I have a component that is subjected to a couple Tc and is restrained in two places P1 & P2. I want to work out what the reactions are on P1 & P2 so forces F1 & F2 respectively. Note that I have neglected self weight of the part as it is insignificant compared to the coupling forces. My method is to take the sum about to places firstly at P1 to give me F2 than about O to give me F1. Is this the correct approach to the problem ?. Any help welcome.

A

 

[zekeman]

Has nothing to do with strain energy.Two pipes in two holes.
I'll give one example similar to OQ' slot idea.
One bracket hole is circular and has a very small clearance with one pipe while the other bracket "hole" is a parallelogram, loosely fitted around the other pipe. Now rotate the bracket around the circular hole and see what you get.

 

[galaxy212]

I think the time has come to get the FEA out on this problem. Ill try and let you all know what results I get on the reactions for closure.

 

[rb1957]

good lord, pls don't ... it's like using a sledge to open a peanut.

@zeke, the point is that there is a redundant load (along the line 1-2) that can't be determined by equilibrium, but any load in this direction (applied at 1, reacted at 2) effectively reduces the arm for the couple, ie increases the resultant force and so increases the strain energy in the plate. minimum strain energy is a solution for redundant structures, and i suspect/propose that the minimum strain energy solution has the longest effective arm, the smallest couple.

Quando Omni Flunkus Moritati

 

[zekeman]

"@zeke, the point is that there is a redundant load (along the line 1-2) that can't be determined by equilibrium, but any load in this direction (applied at 1, reacted at 2) effectively reduces the arm for the couple, ie increases the resultant force and so increases the strain energy in the plate. minimum strain energy is a solution for redundant structures, and i suspect/propose that the minimum strain energy solution has the longest effective arm, the smallest couple. "

Rb,
Read my post.
Not for the scenario I propose where there are pipes in two loosely fitted holes. There is a real answer for this.

 

[chicopee]

Draw a line between P1 and P2 and locate the midpoint; then calculate the torques from P1 and P2 around that mid point and relocate F1 and F2 to that midpoint and they should cancel out but the resultant torque remains about that midpoint from which you can calculate P1 and P2 which they should be equal but have opposite directions..

 

[rb1957]

you mean divide the applied torque by the distance 1-2 ?

Quando Omni Flunkus Moritati

 

[chicopee]

Yes rb1957,since P1=P2. By the way the directions of P1 and P2 will be different than those shown on the original sketch.