- #1

patrickv

- 5

- 0

Hello all, I need some desperate help. I have a product that is mounted on four corners with 1/4-28 bolts with a shank diameter of .25. The product is mounted to a vibe table and shaken at 20g in each of the three axis. I am currently analyzing the stresses induced in the fasteners in order to prove that a .1875 diameter shank will suffice.

My problem is this:

I am fairly confident I've calculated the tensile and shearing stresses caused by the three different loads (20g in each direction, one at a time) on each fastener.

However when I calculate the torsion in each screw and then the subsequent shearing stresses caused by that moment [tau=(moment)(radius)/(.5)(pi)(r^4)], the stresses are so large, they can't be right. Please help, the attached pdf shows a diagram of the part, numbers and my calcs. I believe I'm approaching this wrong, but I can't tell where. Thank you in advance!

My problem is this:

I am fairly confident I've calculated the tensile and shearing stresses caused by the three different loads (20g in each direction, one at a time) on each fastener.

However when I calculate the torsion in each screw and then the subsequent shearing stresses caused by that moment [tau=(moment)(radius)/(.5)(pi)(r^4)], the stresses are so large, they can't be right. Please help, the attached pdf shows a diagram of the part, numbers and my calcs. I believe I'm approaching this wrong, but I can't tell where. Thank you in advance!