Shear stress on a bar with a bend

[triindiglo]

Homework Statement

I have encountered this problem several times in class, but have never really understood it. There is a solid round bar that is fixed on one end, and that bends 90 degrees a ways down. At the free end of the bar there are forces applied in each Cartesian direction.
Like this: http://farm4.static.flickr.com/3448/4559398860_d6c6e250a0_o.jpg"

The question is to determine the shear stress $$\tau$$_xy at point A (on the outer edge of the tube, radially parallel to the z-axis).

Homework Equations

Torsion - $$\tau$$ = Tc/J
Beam - $$\tau$$ = VQ/It

The Attempt at a Solution

I plug in my values in the above equations, and add them up depending on the shear direction, but I don't seem to get the right answer.

I'm hoping someone can help me with the general idea for this type of problem or point me to a website that explains it clearly.

Thanks!

 

[Mapes]

What values are you using for the torque and the shear force?

 

[triindiglo]

Here is what I tried:

F_x=500lbf
F_y=-800lbf
T=F_y14in
c=r (radius)
J=pi*r⁴/4


which gives torsion shear=-16900psi

V=F_y
Q=y'A'
y'=r
A'=pi*r²/2
t=r

with beam shear=-2844psi

total shear (xy)=torsion shear-beam shear

It's been a while since I was actually in Mechanics of Materials, so that might be way wrong though :).

 

[Mapes]

It's been a while for me too, but isn't y' the distance to the centroid of the top or bottom half of the cross section?

 

[triindiglo]

ah, yes you are right. Unfortunately I don't have the correct answer in front of me anymore so I can't check if that's all that is wrong.

Hopefully the other stuff looks right though?

 

[Mapes]

Yep, the torsion part looks good.