Jonathan Fraser METEOR Project P07102 Environmental Test Stand Project Manager/Lead Engineer Detail Design Review Report

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1 Jonathan Fraser METEOR Project P07102 Environmental Test Stand Project Manager/Lead Engineer Detail Design Review Report The project, P07102 Environmental Test Stand, is specifically involved in the design, manufacture, testing and characterization of a high gravity load centrifuge, and an environmental test stand for simulating the thermal vacuum as associated with space flight. The characteristics of the centrifuge structure include an electric motor specifically designed to accommodate the projects needs, a large, 16 foot diameter centrifuge structure, which rotates at 86 revolutions per minute to create up to 20 times the normal force of gravity here on Earth. Also included in that structure is a custom designed supporting structure to provide balance and a rigid connection to the ground. The thermal vacuum will be used to simulate the thermal gradient that space flight would create, using both the radiation heating of the sun, and the infinitely deep heat sink of space. Along with the thermal gradient, a pressure gradient will also be simulated. This pressure gradient is 10-3 torr which is 10-4 psia. The goal is to have the rest of the RIT components be tested in these systems for certification of space flight. The centrifuge arms were first analyzed using a free body diagram to determine the forces on the arm structure. Since the arm structure is symmetric on both sides of the axis of rotation, only one arm needs to be analyzed. Also one assumption that was made was the center of gravity is in the center of the arm structure. This assumption is valid because the structure itself is symmetric about is center of gravity, and it is made of similar densities of materials (structural steel is the only building material used in these arms). Since this analysis was done in Excel it is very adaptable to the varying geometries of each design iteration. Another good trait is that a complete and thorough weight estimate of each piece can be done with the sizes and densities of each piece. This weight estimation was used to further enhance the accuracy of the free body diagram. One of the very large key components of the inertia loading is the time duration of any acceleration or deceleration. To avoid any large forces this arm structure will need to be sped up very slowly. A time of 5 minutes may be needed in order to have the system accelerate and decelerate slowly enough to reduce loading on the connecting structure. Ideally the acceleration and deceleration curves would look like an over damped system, where the changes in slope, or impulse, would be very low. This was contrary to our initial concepts. These longer periods would also allow for the longest possible life of the structure and potentially mitigate any vibrations induced at a specific point. Once the reactions were solved in the free body diagram, bolts could be selected. The bearing forces, and shear forces could then be calculated, and the per bolt loadings could then be derived. The clamping forces and torques for each bolt could also be found at this point. These 16 one inch diameter SAE grade 5 bolts will be enough to carry the loads in a worst-case scenario. Once everything was modeled and the bolt holes created, a finite element method analysis was completed on several key parts. The arm structure had all loadings in place; both induced by gravitation (perceived by rotation and normal gravity forces), and an

2 inertia loading to create the worst case loading, a factor of safety of 10 was used in the initial set of analysis. The bolt holes were constrained as the zero datum. The mesh was created in an automatic fashion (Figure 1). However, refinement did happen around the bolt holes at the end of the beam, and at the mounting holes for the rocket safety chamber. Overall there are 32,039 elements in this mesh, with more then 1400 elements around each hole. Mesh of Centrifuge Arms 32,039 Elements Figure 1 During this analysis, the forces were more then sufficient enough to destroy the flange of the c channels we had used. In this case, the area around the bolts would begin to tear and rip a small portion of steel away, causing catastrophic failure (Figure 2 and Figure 3).

3 Stress Analysis With Inertia Figure 2 Stress Analysis on Bolt Area With Inertia Figure 3

4 Static Stress Analysis Figure 4 Static Stress Analysis on Bolt Area Figure 5 With no inertia forces, the loading once again caused the structure to fail in the same scenario (figure 4 and figure 5). However, with lower loadings, the structure can survive. A factor of safety of three is the best this structure can manage. Any larger number and the arms begin to experience plastic deformation. While this deformation would provide for enough time to turn the test off, it would render the arms unusable for further tests. Total failure occurs at a factor of safety of 5.5. When the analysis reaches a factor of safety of 10, the total deformation of the arms is.17 inches (Figure 6).

5 Static Deflection Plot With No Inertia Figure 6 However, the previous truss structure has a factor of safety of 7 in its current design state. With the factor of safety at 10, the structure will fail, however, this occurs in an area that will be welded. The assumptions that occur with welding would make the welded area as strong as the steel itself, possibly more so. Nevertheless, by specifying different types and styles of welds, this area could be further strengthened. This truss structure was not pursued further at the time it was presented because of the cost of welding. The top and bottom connecting plates are the main structures that hold the centrifuge together, it is one inch thick and twenty inches long, and spans the width of the structure. The plate has a connection for 16 bolt holes. These bolts are one inch in diameter. Since this plate carries the majority of the loading for the structure it must be robust and have a large factor of safety. Once again the finite element method analysis was done on this part to confirm the strength of the system. Under the simulation, the bolt holes on one side were all constrained, and the bolts on the other side were all loaded with double the calculated load for one side in order to get the full tension effects of the extreme loading. The plate was design under these assumptions and with a factor of safety of 10, thus this meets the factor of safety goals. The top plate was meshed and has 8,862 elements with the mesh being refined on the area that is most likely to fail, which is the first constrained bolt hole location (Figure 7).

6 Mesh of Top and Bottom Connecting Plate 8,862 Elements Figure 7 The Plate faired well, with a max stress of 9.925E04 psi (Figure 8 and Figure 9), and a max deflection of 9.408E-05 inches (Figure 10), With these stresses and displacements this is the only piece on the upper arm structure that meets the factor of safety goals, this piece is not anticipated to deform plastically under this loading. Static Stress Analysis - Top and Bottom Plate

7 Figure 8 Static Stress Analysis - Top and Bottom Plate Max Stress Bolt Hole Figure 9

8 Static Deflection Plot - Top and Bottom Plate Figure 10 Another concern for whatever style structure is being rotated is vibration. The current design has a natural frequency (ω n) of 2.11 Hertz, as found using similar techniques of finite element method analysis as the previous analysis. However, the program has a level of accuracy of plus or minus ten percent, which could lead this natural frequency to be as low as 1.90 Hertz. This caused a concern because the driving frequency is close to this value; the driving frequency (ω) is 1.43 Hertz.

9 Normalized Frequency Plot of the Arm Structure Figure 11 Decreasing the stiffness (ζ) of this design, or adding more mass will cause the natural frequency to decrease, which would place the entire structure into an area of concern. A normalized frequency plot has been created for the analysis of the structure (Figure 11). When the natural frequency reaches within plus or minus ten percent of the natural frequency beating will occur. Beating will cause the arm structure to flap like a bird, and as the natural and driven frequencies become closer, this beating will become more pronounced until the system destroys itself. Since no member of the team has any previous experience with vibrations, Dr. Lam and Dr. Kempski have provided as much advice as possible in this area. The safety of the structure and the by standers is paramount. Due to the high velocity of the end of the arm, it is traveling at 49.5 MPH, or Ft/S, anything ejected from the arm structure can be considered lethal. However, this scaled down version of the centrifuge is much safer then the larger version first proposed. The larger version has a 125 Kg payload, and if ejected at the above speeds, it carries KJ of energy, as compared to a 15 Kg payload, which carries 3.587KJ of energy. For a comparison, a shotgun slug exiting the muzzle of a gun has KJ of energy. This is lethal enough to kill a deer at over 75 yards. A 9 mm pistol, the kind of handgun law enforcement uses, carries.54 KJ of energy when exiting the muzzle. Once again this is lethal, but over shorter distances, approximately 20 to 40 yards. With this type of very evident safety issues a permanent structure needs to be built to use this test stand. Since the arms are the assembly most likely to fail, a roof may be another option added to this structure. If one of these arms fails, they could potentially cartwheel over any wall or safety fence. If

10 a roof cannot be produced, a large evacuation area may need to be in place. This would need to be an area, which could have a potentially large radius on the order of hundreds of yards. The cost of the entire project is $ 25,061.61, which includes $10, for the centrifuge system and $14, for the thermal vacuum. There is a 12.5% overrun added to the total costs of each system, the above costs include that figure. The most expensive component in the centrifuge is motor that costs $2, The most expensive component in the thermal vacuum is $5,