1 AAE 450 Spring 2008 Steven Izzo March 27, 2008 Structures Tank Buckling & Final Stress Considerations

2 Buckling Analysis and Prevention  Applied buckling load: Mass above x g x g loading  Critical Buckling: method by Baker, Kovalevsky, and Rish.  Code adds support rings until applied < critical  Ring Design: –Rectangular cross section –Same material as tank –Sized using same buckling analysis  Final rings needed: 0 –Final design required shorter/thicker tanks.

3 AAE 450 Spring 2008 Structures  Research stress sources  Modify numbers in code  Check for failure/sizing change Method Thrust vectoring, engine misalignment, spin stabilization, material property temp. variance, thermal expansion, acoustics Stresses Investigated Final Stress Considerations Result All stresses check out, no resizing is necessary

4 AAE 450 Spring 2008 Structures Tank Mounting/ Buckling Prevention Design Rocket Body Tank Support Rings Rivets Original DesignFinal Design Original design for tanks to be manufactured separately, secured in place by external skin and riveted support rings, tank not riveted or welded in. Later determined that tank was the outer skin, so support rings weld inside it.

5 Tank Mounting/ Buckling Prevention Design  Original critical buckling load method: –Euler  Final critical buckling load method: –From Baker et. al –This method more accurate for thin shell structures Curvature parameter Buckling Coefficient Critical Buckling Load  Support Rings add material to take the stress and cut the length of the tank into parts, raising the critical load

6 Stresses Thrust Vectoring- Run structures code for each payload, adding bending equal to thrust at increasing angles 0 to 90 degrees, look at numbers for stringers/hoops Result: Number of stringers/hoops did not change at all, even for 90 degrees. No extra structure restriction on thrust vector. Engine/Thrust Misalignment- Same procedure as thrust vectoring, but also tried inputting thrust into shear. Result: Number of stringers/hoops did not change, even 90 degrees. No extra structure restriction on misalignment. Spin Stabilization- No simple analysis available for torsion from spin stabilization. Increasing shear inputted into code until rocket would need to be resized, angular velocity rate found from force. Result: Spin-up rate must not exceed approximately 170 rpm/sec

7 Stresses Material Property Variance- Source: Middle and extreme values inputted into code. For this range, which is extreme, rocket did not fail or require extra support.

8 Stresses Thermal Expansion- Materials have all been designed to be assembled with the same materials, and most of the rocket is Aluminum, therefore thermal expansion can be ignored Acoustics- A complete vibration/ dynamic loading analysis by Finite Element Analysis is still being worked on by the structures group. All sources show that acoustic vibrations in solid propellant rockets are small. Sources also show that the ground is a major amplifier in acoustic vibrations, which is eliminated with a balloon launch. A complete FEA will be worked out soon. Approximate general bending before a resize is necessary: 1E9 Pascals Approximate shear: 30e4 Pascals Code adds support to prevent failure, will always output how to improve rocket, but if extra support structures are needed, rocket must be resized to insure success.

9  Steven Hiu and all contributors to the function tanksv2.m  David Childers- cost functions  Brandon White- assistance with buckling  Shurn, Stephan. “Thrust Vector Control.” February 28,  Stuart, Jeff. “Spin Stabilization of Third Stage(200kg Payload).” February 28,  Waite, Adam. “Analyzing Loading Based on Test Design.” February 21,  Wilcox, Nicole. “Thrust Offset Angle- Hybrid and Solid.” February 28, Class Sources

10 Outside Sources  Baker, E.H., Kovalevsky, L., Rish, F.L. Structural Analysis of Shells, Robert E. Krieger Publishing Company, Huntington, NY,  Bedford, A, Fowler, W, Liechti, K. Statics and Mechanics of Materials, Prentice Hall, Englewood Cliffs, NJ,  Boddy, J, Mitchell, J, & Harris, L. “Systems Evaluation of Advanced Structures and Materials in Future Launch Vehicles.” AIAA Journal no ,  Bruhn, E.F. Analysis and Design of Flight Vehicle Structures, “Buckling Strength of Monocoque Cylinder”, S.R. Jacobs,  Green, E.A. & Coulon, J.F. “Cost Considerations using Titanium,” AIAA, New York, NY,  Klemans, B. “The Vanguard Satellite Launching Vehicle” The Martin Company, Engineering Report No , April  Pisacane, V & Moore, R. Fundamentals of Space Systems. Oxford Press, New York, NY  Sarafin, T. Spacecraft Structures and Mechanisms: From Concept to Launch. Microcosm, Inc. Torrance, CA  Sun, C.T. Mechanics of Aircraft Structures. John Wiley & Sons, New York, NY  McMaster Carr online catalog  Titanium Joe online catalog