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The Hermes Pseudo Forward Closure is designed to bring a smile to the face of tired rocketeers as they prep for flight. Eight 8-32 bolt holes affix the closure to the extension tube. Moderate mass saving cuts decrease the weight.
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- Stress is clearly concentrated around the bolt holes. Solidworks simulations historically exaggerate stress in these areas.
- As I previously mentioned, my chosen forces are overestimates.
- When the U-bolt is attached, it isn't going to be threaded into the smiley face's "eyes," which is what my simulation currently implies. Instead, it will be affixed a long, bar on the other side and then nuts. This bar will distribute the load better than my simulations show.
Bolt Strength:
Using Size 4-40 bolts
There are 8 bolt holes. Assuming that they are size 4-40, the distance from the bolt hole center to the edge is > 1.5 times that of the bolt diameter (~1.67).
Bolt shear is estimated as 0.6*60,000psi = 36,000psi per bolt. Then, estimating bolt area using the minor diameter yields pi*(0.0805/2)^2 = 0.00509 in^2. Then, estimated shear force is ~183 lbs per bolt. Given that there are 8 bolt holes, this gives an estimated shear force of 1465.8 pounds.
Using Size 6-32 bolts
Assuming that they are size 6-32, the distance from the bolt hole center to the edge is < 1.5 times that of the bolt diameter (~1.36).*
The new minor diameter yields an area of pi*(0.0989/2)^2 = 0.00768 in^2. Then, estimated shear force is ~277 lbs per bolt. Given that there are 8 bolt holes, this gives an estimated shear force of 2212.5 pounds, which is good, given that the webbing will break at around this force, anyways.
*Note that if we increase thickness of the closure from 0.375" to 0.5", this number increases to 1.8.