The Graben Internal Structure

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:. Asteroseismology
:. Dark Matter Galaxies
:. EPR
:. Gravitophotons
:. Hybrid Rocket Engine
:. Pulse-Ram Induction

:. Sections:

:. Disclaimer
:. Purpose
:. Theory
:. References

:. Components:

:. Combustion Chamber
:. CDN Nozzle
:. Gasoline Tank
:. Injector System
:. Internal Structure
:. Launch Control
:. Pressure Manifold
:. Pressure Tank
:. Propellants
:. Solid Fuel and Ignition
:. T-stoff Tanks
:. --

:. Data:

:. CFD CDN01
:. FEA Combustion Chamber
:. FEA F-02
:. FEA F-03
:. FEA F-04
:. FEA F-05
:. FEA F-06
:. FEA F-07
:. FEA T-stoff Flange
:. Pressure Tank Test

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Computer model of the internal structure

The Internal Structure:

The internal structure will be composed of a series of aluminum flanges mounted on threaded aluminum rods. Most hobby rockets use solid fuel systems so their tubes are mainly filled with flight computers and recovery systems. Unfortunately, the hybrid system used in this design is a bit more complicated and requires us to launch all the components necessary for the engine to function. So, the purpose of the internal structure is to hold all the internal components in place during operation. A secondary purpose is to add strength to the rocket, thus allowing us to use a thinner skin. The downfall to the internal structure is that it will add more weight.

The internal structure construction:

The design was dictated by the components required for operation. Since we are basing the engine on older designs, we have to launch a pressure system, an oxidizer system, an ignition system, and a recovery system. The flanges will be made from 1100 Aluminum Alloy 1/16 inch thick and will be designed based on location and function. After the flanges were roughly designed we preformed an FEA simulation of the "worst case scenario" on each flange, see FEA in the data section, to determine how the flanges would react and where their weaknesses are located.

FEA simulation of F-02

Proposed flanges.

Since nearly all the flanges appear to be able to survive their "worst case scenarios", we can theoretically trim them down in low stress areas if weight becomes an issue. Since the FEA is just a simulation, we will also need to make a flange to test and compare the results with the computer model. The flanges are cut from a single sheet of aluminum using a circle cutter specially designed for use on a drill press. The aluminum blanks were then machined to match the designs. When all the flanges are complete, they will be mounted to three T6-6061 Aluminum alloy threaded rods using aluminum bolts. When the location of each flange is finalized the bolts will be tightened and secured with locktite.

Sheet of T6-6061 AL alloy.	Drill bit used to cut the flange blanks.
Flange template	Preparing the flange for trimming.
Finalizing one of the flanges.	The flange blanks.

1100 Aluminum Alloy

Physical Properties	Metric	English	Comments

Density	2.71 g/cc	0.0979 lb/in³
Mechanical Properties

Hardness, Brinell	28	28	AA; Typical; 500 g load; 10 mm ball
Tensile Strength, Ultimate	110 MPa	16000 psi	AA; Typical
Tensile Strength, Yield	103 MPa	15000 psi	AA; Typical
Elongation at Break	12 %	12 %	AA; Typical; 1/16 in. (1.6 mm) Thickness
Modulus of Elasticity	68.9 GPa	10000 ksi	AA; Typical; Average of tension and compression. Compression modulus is about 2% greater than tensile modulus.
Poisson's Ratio	0.33	0.33
Fatigue Strength	41.4 MPa	6000 psi	AA; 500,000,000 cycles completely reversed stress; RR Moore machine/specimen
Shear Modulus	26 GPa	3770 ksi
Shear Strength	68.9 MPa	10000 psi	AA; Typical

T6-6061 Aluminum Alloy

Physical Properties	Metric	English	Comments

Density	2.7 g/cc	0.0975 lb/in³
Mechanical Properties

Hardness, Brinell	95	95	AA; Typical; 500 g load; 10 mm ball
Hardness, Knoop	120	120	Converted from Brinell hardness.
Hardness, Rockwell A	40	40	Converted from Brinell hardness.
Hardness, Rockwell B	60	60	Converted from Brinell hardness.
Hardness, Vickers	107	107	Converted from Brinell hardness.
Tensile Strength, Ultimate	310 MPa	45000 psi	AA; Typical
Tensile Strength, Yield	276 MPa	40000 psi	AA; Typical
Elongation at Break	12 %	12 %	AA; Typical; 1/16 in. (1.6 mm) Thickness
Modulus of Elasticity	68.9 GPa	10000 ksi	AA; Typical; Average of tension and compression. Compression modulus is about 2% greater than tensile modulus.
Notched Tensile Strength	324 MPa	47000 psi	2.5 cm width x 0.16 cm thick side-notched specimen, Kt = 17.
Ultimate Bearing Strength	607 MPa	88000 psi	Edge distance/pin diameter = 2.0
Bearing Yield Strength	386 MPa	56000 psi	Edge distance/pin diameter = 2.0
Poisson's Ratio	0.33	0.33	Estimated from trends in similar Al alloys.
Fatigue Strength	96.4 MPa	14000 psi	AA; 500,000,000 cycles completely reversed stress; RR Moore machine/specimen
Fracture Toughness	29 MPa-m½	26.4 ksi-in½	KIC; TL orientation
Machinability	50 %	50 %	0-100 Scale of Aluminum Alloys
Shear Modulus	26 GPa	3770 ksi	Estimated from similar Al alloys
Shear Strength	207 MPa	30000 psi	AA; Typical