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- Ensuring safe transfer of load at the payload bulkhead if only using 2 bolts and a reduced thickness of endplate.
- Ensuring that taken together, the 4 tie rods could theoretically take all 360lbs of force in compression/tension (I want to cover all my bases here).
- Check thread pullout/break strength at the connection between the tie rod and the diaphragm
- Check rod buckling strength with steel (and aluminum since we might change to aluminum)
Selected Piston Dimensions, Calculations, and Improvements
The relevant dimensions and properties of 6453K153 are enumerated in the table below:
| Bore Diameter (in) | Bore Material | Stroke Length (in) | Rod Material | Rod Diameter (in) | Total Length (baseplate to baseplate; in) |
|---|---|---|---|---|---|
| 1-1/8" | Aluminum | 5.5 | 303 Stainless Steel | 3/8" | 7.75 |
Given a 4.5" coupling section, this gives us a 1" margin on separation distance.
Rod
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Material Improvement
The rod can be improved by making it out of aluminum instead of stainless steel. An We can estimate for mass savings is calculated below:the mass savings by knowing that the approximate piston rod volume is 0.911 in3, the density of 303 stainless steel is 0.289 lb/in3, and the density of 6061 aluminum is 0.0975 lb/in3. Given this information, replacing the steel rod with one made from aluminum will save approximately 0.174 lbs.
Buckling Calculation
We need to ensure that the rod of the piston will not buckle when it transfers load to the diaphragm. To perform these calculations we know that the tensile modulus of steel is 28000 ksi and the elastic modulus of aluminum is 10000 ksi.
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Given the area moment of inertia for a circular cross section is:
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Pcr,steel = 15,765 lb and Pcr,aluminum = 5,630 lb
As you can see, both steel and aluminum rods have large factors of safety on buckling due to piston force.
Resources:
The following resources are useful materials for learning about pressure vessel and piston theory:
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