Design Of A
Compression
Panel
Delft University of Technology
E10E
This page is intentionally left blank.
iii
Cover picture is own work.
Contents
1 Introduction
1
2 Literature study
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
Flat Plate Assumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cause of Compression Forces on Launcher Panel . . . . . . . . . . . . . . . . . . . . .
Other Forces Acting on the Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Temperature Effect on the Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Panel as a Part of the Cryogenic Fuel Tank Structure . . . . . . . . . . . . . . . . . . .
Panel Production Plan Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Importance of Correct Clamping During Testing . . . . . . . . . . . . . . . . . . . . .
Deviations in Manufacturing and Testing of the Panel . . . . . . . . . . . . . . . . . .
Panel Testing Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 Design of the Panel
4
3.1 Design Requirements and Constraints of the Panel . . . . . . . . . . . . . . . . . . . .
3.1.1 Functions of the Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.2 Requirements of the Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.3 Constraints of the Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.4 Assumptions made for the Panel . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.5 Free Variables of the Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Panel Design Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Free Body Diagram of the Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4 Determination of Design Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.1 Thin Sheet Buckling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.2 Column Buckling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.3 Rivet Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.4 Panel Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.5 Final Panel Design Parameters and Failure Modes . . . . . . . . . . . . . . . . .
4 Manufacturing of the Panel
5 Testing of the Panel
13
14
14
14
14
15
Description of Test Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Description of Test System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Description of Test Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Plots of Received Test Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 Analysis of the Panel Test
6.1
6.2
6.3
6.4
4
4
4
4
5
5
5
6
7
7
8
9
10
12
13
4.1 General Description of Production Plan . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Post Manufacturing Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2.1 Deviations Between Design and Built Panel . . . . . . . . . . . . . . . . . . . .
4.2.2 Feedback from Manufacturing Department . . . . . . . . . . . . . . . . . . . .
4.2.3 Deviations Between Estimated and Actual Hours . . . . . . . . . . . . . . . . .
5.1
5.2
5.3
5.4
2
2
2
2
3
3
3
3
3
15
15
16
16
19
Description and Explanation of Failure Area/Location . . . . . . . . . . . . . . . . . .
Description and Explanation of Failure Type. . . . . . . . . . . . . . . . . . . . . . . .
Comparison of Test Data with Failure Load/Mode Calculation . . . . . . . . . . . . . .
Assessment of the Production Quality in Relation to Testing Outcome . . . . . . . . .
6.4.1 Visual analysis of riveting error . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.4.2 Visual analysis limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.4.3 Visual analysis results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.4.4 Measured results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
i
19
20
22
22
23
24
24
25
Contents
ii
7 Conclusion and Recommendations
26
Bibliography
28
Appendices
28
A Gantt Chart
29
B Production Plan
32
C Aluminium properties
50
D Rivet properties
51
E Panel Analysis Image
52
List of Symbols
kg/m3
ρ
Density
σ
Normal stress
MPa
σcr
Critical buckling stress
MPa
σi r
Inter-rivet buckling stress
MPa
A
Cross-sectional area
m2
b
Stringer pitch
mm
E
Young’s modulus
GPa
F cr
Critical buckling load
kN
F ul t
Ultimate failure load
kN
I
Second moment of area
Kc
Compression buckling coefficient
M
Bending moment
kNm
n r i vet Number of rivets
-
n st r
Number of stringers
-
Q
First moment of area
mm 3
q
Shear flow
kN/m
s
Rivet spacing
mm
t
Sheet thickness
mm
V
Shear force
kN
y
Distance from the neutral axis
mm
mm 4
-
1
Introduction
When a rocket launches, hundreds of thousands newtons of thrust push the rocket up into the air.
Meanwhile, gravitational and aerodynamic forces push the rocket from the other side. One could
compare a rocket launch with a pencil in a hydraulic press; they both would experience high compression loads. To make sure the payload arrives safely in space, the rocket skin must survive its
whole journey. To withstand these massive compression forces the rocket skin consists of numerous compression panels.
These panels are basically the rocket’s skeleton and carry most of the loads during launch and flight.
Just like how a human would not be able to walk without a skeleton, a rocket would not be able to
fly without its compression panels. That is why a properly engineered compression panel is very
important.
The purpose of this report is to explain the function of the side panels of a launcher and the purpose
of the project described in this report is to design the panel itself whilst making sure it complies with
the requirements given by the IAC. When creating a launch vehicle to transport payload to space,
some of the parts that seem simple to manufacture are usually crucial to the success of the mission.
Without the outside panels of the launcher, the interior components would be crushed under the
forces generated when taking off. To design the panels for launch, three parts will be taken into
account:
• The panel;
• The stringers (reinforcement);
• The rivets (the connection between the previous two parts).
Each part must be designed carefully so none of them fails during a mission. This panel is designed
specifically for the G.E.O.R.G.E. launcher from DELTA, i.e. this design process is unique for this application as the loads and requirements may differ from company to company or from mission to
mission. However, the method used to determine the panel measurements can be used to design
compression panels for other launchers and missions.
This report will first cover a literature study on the topic at hand in Chapter 2, which will then lead
on to discussing the design results, the choices made for the design and the justifications for those
choices in Chapter 3. Chapter 4 will outline the manufacturing process and compares and evaluates
the produced panel with regard to the manufacturing plans. Chapter 5 describes the test procedure
and the results obtained from it. In Chapter 6, the data from Chapter 5 will discussed more indepth. Finally, the report will be closed off by Chapter 7, in which the final conclusions will be
given, together with recommendations for similar projects in the future.
1
2
Literature study
The literature study clarifies the main theory that is crucial to consider and understand in designing
a compression panel. This theory provokes allows for a deeper understanding of how a compression
panel is properly designed, tested, and used. Each section in this chapter covers a part of this theory.
2.1. Flat Plate Assumption
A compression panel of a launcher can be assumed to be a flat plate due to its flat and uniform
nature. The forces acting on the panel are distributed uniformly through it and the stress in the
panel is the same everywhere [1]. This allows for the assumption that the panel can be considered a
flat plate.
2.2. Cause of Compression Forces on Launcher Panel
The compression forces seen on a launcher skin panel are due to the acceleration that the launcher
experiences. During lift-off, a high amount of thrust produced by the propulsion system is needed
to overcome the gravitational acceleration. This upwards acceleration causes a force in the direction
of the acceleration. This force is opposed by the atmospheric drag and gravity. These counteracting
forces cause internal force in the skin panels. This ultimately translates to a compression force on
each of the skin panels [2].
2.3. Other Forces Acting on the Panel
During launch there are several dynamic forces that act throughout the launcher. Apart from the
compression forces caused by the thrust and gravity there are also sinusoidal loads and acoustic
loads.
The fast increase in thrust and the combustion in the engines causes vibrations in the launcher.
These vibrations introduce very high levels of low-frequency acceleration in the whole rocket.
Besides, rocket engines are very loud. So loud even that they introduce acoustic loads in the rocket
in the form of high frequency vibration. Next to the noise of the engines, acoustic loads are also
caused by the separation of the airflow along the rocket and the aerodynamic noise [2].
2.4. Temperature Effect on the Panel
During launch the rocket will accelerate to very high speeds. In high speed flight aerodynamic forces
cause the skin panel of a rocket to heat up. The heated up skin will expand and the expansion will
cause buckling if not accounted for in the design of the supporting structure [3].
2
2.5. Panel as a Part of the Cryogenic Fuel Tank Structure
3
2.5. Panel as a Part of the Cryogenic Fuel Tank Structure
By integrating the compression panel in the fuel tank structure it is possible to make the structure
thinner and lighter. This is called a pressure stabilized structure. In cases where this is used the
structure of the rocket is basically inflated like a balloon, which allows it to carry the loads of launch..
An example of this was used in the Centaur upper stage, which used an unusually thin skin and was
therefore very light. The drawback of this sort of structure is that depressurization leads to the entire
rocket failing.[4].
2.6. Panel Production Plan Objective
The objective of a production plan is to outline how a product is manufactured. It provides a stepby-step process detailing what needs to be done to make that product. From the production plan
someone working on production needs to be able to clearly see what is expected of them while
making the product [5].
2.7. Importance of Correct Clamping During Testing
Without proper clamping, the specimen could move around during testing and end up in positions
that would lead to uneven distributions of compression loads. This would generate a concentration
of forces in certain areas, increasing the chance of observing unexpected modes of failure during
testing. This also means we cannot use the test data, as the testing procedure was not followed and
the control variables were not controlled.
2.8. Deviations in Manufacturing and Testing of the Panel
If dimensions of the rivets compared to the dimensions of the holes were to be smaller than planned,
the beneficial effects on the strength of our panel due to the filling of the hole with a rivet would decrease.
Also, if the temperature of the testing environment changed drastically, the thermal expansion of
the material could influence the compression load capabilities of the panel. If the stringer shrinks
more than the panel itself due to lower temperatures, for example, this will generate extra loads in
the panel on top of the compressive loads. This would make the panel fail at lower loads than it
would have if the panel and stringers extended equally.
Most deviations in manufacturing and testing could influence the compression load of the panel,
as to make a reliable test the conditions must be very controlled and precise so any minor change
could influence the results.
2.9. Panel Testing Standards
The standards for testing a panel in compression are referred to as ASTM-E9.The specimen is subjected to an increasing axial compressive load; both load and strain may be monitored either continuously or in finite increments, and the mechanical properties in compression determined [6].
3
Design of the Panel
In this chapter, the process of obtaining the final dimensions and layout of the panel design is discussed. Firstly, the constraints and requirements for the mission will be stated in Section 3.1. Followed by a general description of what the design will look like, together with some dimensions
(Section 3.2). Next, in Sections 3.3 and 3.4, the process of calculations for the design is explained.
3.1. Design Requirements and Constraints of the Panel
The following design considerations for the compression panel are obtained from the IAC [5].
3.1.1. Functions of the Panel
As indicated in the Introduction (Chapter 1), the function of the compression panel is to withstand
the compressive forces during a rocket launch when it is fitted in the fuselage of a rocket. Another
function of the panels is to protect the payload that the rocket transports.
3.1.2. Requirements of the Panel
The following requirements apply:
• The panel must only buckle above 34.5[kN ];
• Failure of the panel must occur at 40[kN ];
• The panel design must be optimised for minimum weight.
3.1.3. Constraints of the Panel
Besides, the following design parameters are constrained (according to the project reader [5]):
• Material: the panel and stringer material is aluminium. For the material properties of aluminium, please refer to Table C.1 in Appendix C;
• Outer dimensions: the plate has the following fixed outer dimensions: 495[mm] x 400[mm]
(±0.5[mm]);
• Plate type: although the plate choice is a free variable, there can only be a plate type chosen
from two pre-defined plates, see also Table 3.1, from [5];
• Stringers: although the stringer choice is a free variable, there can only be a stringer type
chosen from four pre-defined, L-shaped, stringers. For these stringer types, please refer to
Table 3.2, from [5];
• Stringer orientation: the stringers must be orientated in the longitudinal plate direction. Therefore, the stringers are 495[mm] long;
• Rivet type: although the rivet choice is a free variable, there are only two rivet options available: one with a grip length of 1.5 − 3.0[mm] (short rivet) and one with a grip length of 3.0 −
4.8[mm] (long rivet). The properties of the rivets can be found in Table D.1, Appendix D;
4
3.2. Panel Design Description
5
• Rivet positioning: due to clamping, a zone of 35[mm] measured perpendicular from the short
panel end (the 400[mm] end) must be free of rivets.
Table 3.1: Available face sheet thicknesses. From [5].
Face sheet type
Thickness [mm]
F-1
F-2
0.8
1.2
Table 3.2: Available Stringer types. From [5].
L-profile stringer type
Dimensions [mm x mm x mm]
Length [mm]
L-1
L-2
L-3
L-4
20 x 20 x 1.5
20 x 20 x 2.0
15 x 15 x 1.0
15 x 15 x 1.5
495
495
495
495
3.1.4. Assumptions made for the Panel
The following assumptions have been made in order to determine the optimal design:
• The stringer on a panel is assumed to be a uni-axially loaded member or column;
• The section of the panel between two stringers considered to be clamped on all four sides;
• The compression panel is considered as a flat sheet, as explained in Section 2.1;
• The rivet constant for the pop rivets used is assumed to be 2.1.
3.1.5. Free Variables of the Panel
All the above leaves us with the following free variables in the compression panel design:
• The thickness of the plate;
• The type, placement and number of rivets;
• The type, placement and number of stringers.
3.2. Panel Design Description
The design of the compression panel will be as follows. The chosen face sheet type will be F-1 with a
thickness of 0.8[mm]. The panel will be reinforced by seven L-profile stringers of type L-3 oriented
in the same direction (the longitudinal plate direction). The stringer pitch will be 57 ± 0.5[mm],
which is the distance between the centers of two neighbouring stringers, with 29[mm] left on each
side of the plate.
Each stringer has 12 holes (Ø3.2[mm]) of which the midpoints are spaced 38[mm] apart. There is
a 38.5[mm] distance from the top and bottom edges of the stringer to the midpoint of the first and
last hole to make sure the panel can be clamped in the compression test machine. In total, 84 short
rivets are needed to connect all the stringers to the panel. An exploded view of the design can be
found in Figure 3.1 (own work).
3.3. Free Body Diagram of the Panel
6
Figure 3.1: Exploded view of the compression panel (own work)
3.3. Free Body Diagram of the Panel
Figure 3.2: Free Body Diagram of the compressive load on the panel (own work)
The FBD, Figure 3.2, shows the forces acting on the panel. Using Static equilibrium in the y-direction,
we can find that the distributed loads are equal magnitude with opposite direction.
3.4. Determination of Design Parameters
7
3.4. Determination of Design Parameters
3.4.1. Thin Sheet Buckling
The buckling of the panel depends only on the stringer type, amount of stringers and the face sheet
thickness of the panel. Since there are two available face sheets with different thicknesses, the design calculations need to be done for both face sheets in order to determine the most suitable face
sheet. The minimum critical buckling load, as given in Section 3.1, is 34.5[kN ]. However, in order to
calculate the critical buckling load, first the critical buckling stress needs to be calculated for each
panel-stringer combination with Equation 3.1 [5]:
µ ¶2
t
σcr = K c E
(3.1)
b
"σcr " being the critical buckling stress, "K c " being the compression buckling coefficient, "E " being
the Young’s modulus of the material, "t " being the thickness of the face sheet, and "b" being the
stringer pitch. The compression buckling coefficient "K c " is dependent on the " ba " ratio, where "a"
is the unclamped distance between the plate edges on the long side, which is 435[mm], and "b" is
the stringer pitch. The compression buckling coefficient can be read off Figure 3.3, from [7, pg. 458].
Figure 3.3: Buckling concentration coefficient for a buckling plate [7, 458]
Note that for all the panel-stringer combinations, case 1 will be considered, which means that the
panel is clamped on all sides as stated in the assumptions. This has been chosen since the panel
part between two stringers will be clamped by the clamping machine at the short sides and by the
stringers at the long sides. Then, the critical buckling load can be calculated using Equation 3.2:
F cr = σcr A
(3.2)
"σcr " being the critical buckling stress calculated using Equation 3.1, and "A" being the crosssectional area of the plate including the stringers.
3.4. Determination of Design Parameters
8
In order to fulfill the buckling requirement, the value calculated in Equation 3.2 for each panelstringer combination should be at least 34.5[kN ]. This value can be reached by changing the amount
of stringers, which changes both the stringer pitch "b" and the cross-sectional area "A". Note that an
increase of amount of stringers increases the stringer pitch "b", which decreases the critical buckling load, but also increases the cross-sectional area "A", which increases the critical buckling load.
As the effect of increasing cross-sectional area is higher than the effect of increasing stringer pitch,
the critical buckling load will increase when the amount of stringers increases. The results from the
critical buckling calculations for eight different panel iterations can be found in Tables 3.3 and 3.4.
Table 3.3: Critical buckling calculations for face sheet type F-1
Stringer type
Number of stringers
b [m]
Kc
A [m 2 ]
σcr [MPa]
F cr [kN]
Mass [kg]
L-1
L-2
L-3
L-4
7
6
7
7
0.05714
0.06667
0.05174
0.05174
6.3
6.3
6.3
6.3
0.000724
0.000776
0.000523
0.000619
78.4
57.6
78.4
78.4
56.8
44.7
41.0
48.6
0.876
0.938
0.632
0.749
Table 3.4: Critical buckling calculations for face sheet type F-2
Stringer type
Number of stringers
b [m]
Kc
A [m 2 ]
σcr [M P a]
F cr [kN ]
Mass [kg ]
L-1
L-2
L-3
L-4
4
4
5
5
0.1
0.1
0.08
0.08
6.4
6.4
6.4
6.4
0.000711
0.000784
0.000625
0.000694
58.5
58.5
91.4
91.4
41.6
45.9
57.2
63.4
0.860
0.948
0.756
0.839
As can be seen in Tables 3.3 and 3.4, all panel-stringer combinations adhere to the minimum required critical buckling load of 34.5[kN ]. Note that some of these critical buckling load values are
considerably higher than the required value. This is due to the fact that reducing the number of
stringers would lower the critical buckling load to such a value that the panel-stringer combination
does not meet the required value anymore.
3.4.2. Column Buckling
Another failure mode could be due to column buckling where [5]:
F cr =
cπ2 E I
L2
(3.3)
"c" is a constant, in this load case it is 0.25 [5, pg. 21]. "E " is young’s modulus, "I " is the area
moment of inertia and "L" is the free length of the column. To ensure the desired buckling of all
design permutations shown in Tables 3.3 and 3.4 is above 34.5[kN ] we check for all of these designs.
The area moment of inertia of the panel in the xz-plane can be calculated by reducing the shape
into rectangles, calculation of a centroid and using the parallel axis theorem to calculate the new
"I ". The centroid is given by :
Σx i A i
x̄ =
(3.4)
ΣA i
where "x̄" is the centroid measured from the axis in the Figure 3.4 and "A" is the area of each rectangle.
3.4. Determination of Design Parameters
9
Figure 3.4: Cross section view of compression panel, showing the axis system used
For each rectangle the area moment of inertia is given from:
I r ect ang l e =
1
bh 3 + Ad 2
12
(3.5)
"b" is the base length, "h" is the height, "A" is the area and "d " is the distance between the average
centroid and the centroid of the whole body. By using Equation 3.3, 3.4 and 3.5, we obtain the values
in the Tables 3.5 and 3.6.
Table 3.5: Critical force for column buckling, face sheet type F-1
Stringer type
Number of stringers
centroid [m]
I [m 4 ]
F cr i t [kN ]
L-1
L-2
L-3
L-4
7
6
7
7
0.00397
0.00498
0.00159
0.00245
1.63 · 10−8
1.96 · 10−8
4.95 · 10−9
7.05 · 10−9
216
259
65.5
94.4
Table 3.6: Critical force for column buckling, face sheet type F-2
Stringer type
Number of stringers
centroid [m]
I [m 4 ]
F cr i t [kN ]
L-1
L-2
L-3
L-4
4
4
5
5
0.00167
0.00254
0.000872
0.00134
1.07 · 10−8
1.39 · 10−8
3.97 · 10−9
5.71 · 10−9
142
184
52.6
75.7
As is shown in the tables 3.5 and 3.6, column buckling occurs above sheet buckling for all designs
considered. Therefore column buckling will not be a failure mode.
3.4.3. Rivet Spacing
Buckling between rivets can occur. Therefore to ensure the structure buckles above 34.5[kN ], Equation 3.6 can be used [5]:
µ ¶2
t
σi r = 0.9cE
s
(3.6)
"σi r " being the stress applied to the thin plate, and "c" being a constant associated with the rivet
used, in this case 2.1 [5] when being used with pop rivets. "E " is the Young’s modulus of the material,
"t " is the thickness of the thin sheet and "s" is the spacing between rivets.
Since the same material is used for the stringer and the plate, "σi r " can be calculated using Equation
3.7:
σi r =
F · A pl at e
A 2t ot al
(3.7)
3.4. Determination of Design Parameters
10
Table 3.7: Area values used
A t ot al [m 2 ]
A pl at e [m 2 ]
0.000523
0.000320
"A" being the corresponding area on the face the load is applied to, given in Table 3.7.
Using this data, "σi r " calculates to 46.35[M P a]. Rearranging Equation 3.6 for "s" allows the relevant
values to be inputted:
s=q
t
(3.8)
σi r
0.9cE
Table 3.8: Values used in Equation 3.8
Symbol
Value
σi r [M P a]
t [mm]
c [−]
E [GP a]
46.35
0.8
2.1
63.5
This results in a rivet spacing of 40.71[mm]. However, due to the constraints (3.1.3) there is only a
possible length of 425[mm] to place rivets on the panel. Therefore to ensure no buckling occurs, the
calculated value is the maximum rivet spacing. To find the actual rivet spacing the amount of rivets
needs to be known. To find this, Equation 3.9 is used:
n r i vet =
L
s max
+1
(3.9)
"L" being the available length and "s max " being the maximum rivet spacing. This equation gives
a number of rivets to be 11.44. This result is rounded up to 12, ensuring we have more rivets than
required.
To calculate the new rivet spacing, Equation 3.10 is used:
s=
L
n r i vet − 1
(3.10)
This gives a new rivet spacing of 38.64[mm], which is lower than the previous calculation of "s". This
means that the calculations are correct and buckling should not be observed between the rivets at a
load of 40kN . To ensure this is correct, the value can be substituted back in Equation 3.6, and then
Equation 3.7 can be used to calculate the new force required for buckling. This value is 43.98[kN ],
which is above the requirements stated in subsection 3.1.2
3.4.4. Panel Failure
In order to comply with the ultimate failure load of 40[kN ], there are three failure modes that will be
considered in this case. Two of these have to do with the failure of the rivets, and the other one with
the failure of the panel itself. The two failure modes that will be considered for the rivets are tension
stress failure and shearing stress failure. The failure mode for the panel is when its ultimate stress
is reached. At this point the panel will break. These three failure modes need to be checked for the
design parameters that were obtained for the panel buckling calculations. If these design parameters are not sufficient to prevent panel failure up until a compressive load of 40[kN ], then it turns
3.4. Determination of Design Parameters
11
out that the ultimate failure load requirement is more restrictive, hence different design parameters
would need to be decided based on the ultimate failure load requirement in a next iteration.
Table 3.9: Aluminium material properties [5]
σul t [M P a]
σ y [M P a]
E [GP a]
ρ [kg /m 3 ]
127
100
63.5
2780
The failure mode of the panel will first be considered. The material used for the panel is aluminium,
which has the properties shown in Table 3.9, obtained from [5]. To ensure that the panel does not fail
below the ultimate load, the compressive stress in the panel at the ultimate load should stay below
the ultimate strength of the aluminium. This compressive stress can be calculated using Equation
3.11:
F ul t
σ=
(3.11)
A
where "F ul t " is the ultimate load and "A" is the cross-section of the panel on which the load is
applied. The cross-section of the panel is calculated using Equation 3.12:
A = A panel + A st r i ng er ∗ n st r
(3.12)
where "A panel " and "A st r i ng er " are the cross-section of the panel and the stringer, respectively and
"n st r " is the number of stringers. The number of stringers, the cross-section of the selected stringer,
type L-3, and the cross-section of the selected sheet, type F-1, can be found in Table 3.10. The dimensions of these components can be found in Table 3.2 and 3.1.
Table 3.10: Panel properties
A panel [m 2 ]
A st r i ng er [m 2 ]
n st r [−]
2.9 · 10−5
3.2 · 10−4
7
Using Equation 3.12, and the values from Table 3.10, the total cross-section of the panel is calculated, which gives a value of 5.23 · 10−4 [m 2 ]. Now using Equation 3.11, the compressive stress in
the panel at the ultimate load of 40[kN ] can be calculated, which gives a compressive stress of
76.5[M P a]. This is below the ultimate strength of the aluminium and even below the yield strength.
Hence, it turns out that the requirements set on buckling were more restrictive than the failure requirements. A new iteration will thus not be necessary. Furthermore, this means that there is a
safety factor of 1.66 and that the load at which the panel will fail is 66.4[kN ]. The load at which the
panel will start to yield is 52.3[kN ]. Hence, under compression, the panel will go through a sequence
of buckling, then yielding and finally failure.
Lastly, the failure of the rivets will be treated. The way in which rivets lead to failure of the whole
panel is when one of the rivets breaks off due to a shear stress or a tensile stress in the rivet. This
would cause one of the stringers to be locally weakened at the place where the rivet broke off. Since
this rivet break-off causes a larger rivet spacing between its neighbouring rivets, the load at which
inter-rivet buckling occurs will be reached sooner. This would lead to a higher deformation than
anticipated at a given load, which could cause other rivets to break off. This chain reaction would
lead to a rapid collapse, hence a failure of the panel.
3.4. Determination of Design Parameters
12
Since the rivets are not loaded directly, the situation in which the rivets fail is when the panel has already deformed significantly. This would impose a significantly higher load on the rivets. However,
since the panel has been designed such that it buckles at a load higher than 40[kN ], the rivets will
not experience high enough loads which causes them to fail, hence the failure of the rivets will not
be the cause of panel failure.
Having covered all the failure modes of the panel, it can now be determined how the panel will fail.
The applied compressive force will run up to the force at which inter-rivet, stringer and sheet buckling will occur.
The buckling shifts the center of gravity in the z-direction, according to the coordinate system in
Figure 3.2. This causes a small moment arm to form between the applied compressive force and
the center of gravity. This imposes a bending moment on the panel. As the panel keeps bending
slightly due to the moment, the center of gravity shifts more and more, increasing the moment arm,
hence increasing the bending moment. At this point, the bending moment will have lowered the
compressive force at which yielding occurs since there is now not only a normal stress due to the
compression, but also due to the bending moment.
When the normal stress at which yielding occurs is reached, the sheet and stringers deform plastically. When this happens, the forces on the rivets might be high enough that would cause some of
the rivets to break off. This would weaken the panel significantly, as the stringers detach from the
panel. If the load continues being applied, the panel would simply fold in half.
3.4.5. Final Panel Design Parameters and Failure Modes
In Table 3.11 an overview of all the values of the design parameters that had to be determined is
given. These values stem from the calculations in this section.
Table 3.11: Design Parameters
Design Parameter
Value
Face Sheet Thickness [mm]
Number of Stringers [-]
Stringer Pitch [mm]
Stringer Type [-]
Number of Rivets [-]
Rivet Spacing [mm]
0.8
7
57
L-3
12
38
Additionally, the theoretical compressive load at which inter-rivet buckling, thin sheet buckling,
column buckling, panel yielding and panel failure occur are given in Table 3.12
Table 3.12: Theoretical buckling and failure values
Failure mode
Load F [kN]
Inter rivet buckling
Thin sheet buckling
Column buckling
Panel yielding
Panel failure
44.0
41.0
65.5
52.3
66.4
4
Manufacturing of the Panel
In this chapter, the manufacturing process of the panel is briefly described and analysed. First, a
general description of the production plan will be given in section 4.1. Followed by the analysis of
the manufacturing of the panel in Section 4.2. This analysis contains deviations between the design
of the panel and the panel that was manufactured, feedback from the manufacturing department
and finally, deviations between the estimated and actual hours spent on manufacturing the panel.
4.1. General Description of Production Plan
The production plan starts with the required tools and materials for the assembly of the compression panel. This is a simple list with all the parts that are included in the panel followed by a list of
tools necessary in each step of the manufacturing process.
The tools list is followed by a new chapter which is the step-by-step guide on how to manufacture
the panel. This chapter starts with describing the necessary safety precautions both for general work
safety and for the current COVID regulations.
The first section in the actual manufacturing process describes the measuring and marking of all
the dimensions on the panel and the stringers. The section illustrates where to mark the lines and
points that will eventually become the outer dimensions of the panel and the holes for the rivets.
This section also contains some figures which help in portraying the dimensions. This should take
about 20 minutes.
After marking all the dimensions the layout of the parts should be checked. The section for layout in
the production plan gives the layout for the finished panel again providing dimensions and a figure.
Going over these steps should take about 5 minutes.
Now the holes in preparation for the rivets need to be made and all edges need to be finished. In
this section it is outlined in detail how to finish the edges using a hand reamer; how to drill the holes
and how to finish these holes using deburring tools. Figures are also included showing the best way
to fix parts together for precise drilling. Overall this should take up around 55 minutes
Lastly the parts of the panel should be riveted together. In the last section of this chapter and consequently of the production plan, the steps for clamping and riveting the plate and stringers together
are described. Following these steps should take about 30 minutes. A detailed description of how to
use the riveting equipment is also provided.
13
4.2. Post Manufacturing Analysis
14
4.2. Post Manufacturing Analysis
4.2.1. Deviations Between Design and Built Panel
Due to the detailed nature of the provided production plan, there were no manufacturing irregularities that lead to a different panel than the one that was designed.
4.2.2. Feedback from Manufacturing Department
After the manufacture of the compression panel, the manufacturing department provided some
feedback on the production plan :
• The material for the L-stringers was missing and should have been given in Section 2.1 of the
production plan, see Appendix B.
• The manufacturer was instructed to band saw the aluminium sheet to size. This is not necessary because the sheet was already cut to size. Also, using a band saw to cut aluminium sheet
is not appropriate due to the difficulty in obtaining accurate cuts.
• In Subsection 3.2.2 of Appendix B (the Production plan), it should have been specified which
long side of the L-stringer is meant, because an L-stringer has two long sides.
• The orientation of the rivets was missing. It should have been specified at which side of the
plate the heads of the rivets are visible.
• The manufacturer was instructed to drill the holes in the plate and the stringers separately.
This is not the preferred method, as drilling the holes in the plate and the stiffeners at once is
much more accurate.
• In Section 3.2 of Appendix B (the Production Plan), the tolerances during manufacturing were
taken into account. This was very convenient for the manufacturer.
4.2.3. Deviations Between Estimated and Actual Hours
In the production plan for the compression panel (Appendix B), each manufacturing step was given
an estimated time to complete the step. The estimated time for each manufacturing step adds up
to a total time of 110 minutes. The actual time that the manufacturer spent on the manufacturing of the compression panel was roughly 90 minutes. This difference is mainly caused due to an
overestimation of time needed for the clamping and riveting step.
5
Testing of the Panel
In this chapter, the set-up of the test used to analyze the panel is described. In Section 5.1 the
ultimate goal of this test is outlined. After this, Section 5.2 describes the set-up of the test and the
machinery used. Following this is Section 5.3. This section describes what the test is going to look
like and some of the observations made during the test. Finally, Section 5.4 gives a set of graphs
portraying the raw data obtained in the test.
5.1. Description of Test Objective
When producing a part of a complex assembly like a launch vehicle, the design cannot go directly
from Excel calculations to production to being the official part for the launch vehicle; the part has
to undergo testing. The point of testing is to make sure that there are no unexpected failure modes
and unseen production errors.
In the case of a compression panel, the test will display data describing the failure modes and the
strength limits of the panel. This data can then be used to eliminate errors and further improve the
design of the panel to ensure the success of the mission. The testing process can be iterated as many
times as necessary until there is certainty that it will not fail under any expected circumstances.
5.2. Description of Test System
To explore the compression failure loads of the panel, an MTS 311.51 test system will be used. This
system is capable of applying a compression force of up to 3500[kN ], while using an integrated
load cell for measurements of the compression load. The strain suffered by the panel under the
compression loads will be recorded using Laser Displacement Sensors (LDS) for in plane and out
of plain displacement of the panel. This information could aid in the understanding of the failure
modes of the panel (buckling or pure compression failure). A simplified over can be seen in Figure
5.1 from [5].
15
5.3. Description of Test Events
16
Figure 5.1: Compression test machine MTS 311.51 [5]
5.3. Description of Test Events
Firstly, the panel will be inserted into the MTS 311.51 test system. The LDS’s need to be calibrated
to the initial height of the panel to make sure the measurements of the displacement are accurate.
When the test system is turned on it will increasingly load the panel with a compression force. While
the panel is being loaded, the strain of the panel will be measured using laser displacement sensors.
They will measure the in and out of plane displacement. These measurements will be processed
into graphs that later can be used for the analysis of the panel. The loading will continue either until
the panel has compressed 30[mm] or until the test system measures a reaction force equal to 20%
of the max compression force the panel can support, after the panel has failed (how the maximum
force on the panel was calculated as shown in Chapter 4). The test panel will then be removed from
the MTS 311 test system, after slowly unloading.
During the actual test, no signs of failure showed until around a 28[kN ] compression. At this point,
the skin shows signs of inter-rivet buckling and at the maximum load the panel is subjected to
45[kN ] compression. This creates a sharp edge running perpendicular to the stringers and bulging
outward. Apart from the phenomena mentioned above, no signs of failure could be seen and all
rivets survived the test.
5.4. Plots of Received Test Data
Using the received test data, several graphs have been plotted. These graphs can be found on the
pages below; Figure 5.2 (a) shows the values of the laser displacement sensors versus the time. Figure 5.2 (b) shows the difference between LDS 50[mm] number 1 and 2 versus time. Lastly Figure 5.3
shows the compression force versus the displacement in the out of plane direction.
5.4. Plots of Received Test Data
17
(a) LDS measurements
(b) LDS relative accuracy
Figure 5.2: Laser Displacement Sensors measurements vs. time (a) and Difference in measurements from LDS number 1 / 2
(b) (own work).
5.4. Plots of Received Test Data
Figure 5.3: Compression force versus displacement (own work). The insert on the top right is Figure 5.1 from [5].
18
6
Analysis of the Panel Test
The purpose of this test analysis is to give an insight into what can be improved in the compression
panel design. Data analysis allows the responsible researchers to draw conclusions from the data
by representing the data in different ways: table, graphs et cetera. Using this analysis, the design
of the panel can be iterated to better fit the requirements of the mission. This chapter starts off by
describing where the panel failed (Section 6.1), then goes on to explaining how and why the panel
failed (Section 6.2). Next, the test data is compared to the calculations performed previous to the
testing (Section 6.3). Lastly, the production quality of the panel is reviewed with the aim of explaining why the panel failed and what factors possibly influenced the panel failure (Section 6.4).
If the test shows that the panel has not reached the required strength, we can then analyse the location and type of failure of the panel. This information allows for the strengthening of the panel
in appropriate areas. Once this is implemented, the panel is retested until there is absolute confidence that the panel will not fail under the given loads. In addition if the panel over-performs some
corrections can be made to the design with the goal of saving weight.
6.1. Description and Explanation of Failure Area/Location
The failure happened in three main areas:
1. Middle of the panel, in between 2 rows of rivets;
2. Top of the panel, near the clamping;
3. Bottom of the panel, also near the clamping.
The expected outcome was that the middle of the panel would fail, as the middle point on the panel
is the furthest away from the clamps. When the load is not applied perfectly through the center of
mass of the panel, a moment will be created. This moment, is what makes the panel buckle, and the
region of maximum moment is at the maximum distance from the region of loading; in this case this
region is the the middle of the panel. The moment thus led to column buckling. As the whole panel
was bending, it contracted one side of the panel, leading to the inter-rivet buckling. As a result, the
strips experienced plastic deformation as seen in Figure 6.1.
Secondary buckling locations at the top and the bottom near the clamping sites were also visible, as
seen in Figure 6.1. Those were most probably, a result of the secondary bending that happens at the
ends of a clamped plate once it buckles. Once the free middle part of the panel has deformed to an
arc shape, a reaction bending moment is created near the clamped area, due to the inability of the
clamped ends to follow the curve.
19
6.2. Description and Explanation of Failure Type
(a) Full
20
(b) Zoomed
Figure 6.1: Failure Areas of Panel After Testing (own work).
6.2. Description and Explanation of Failure Type
Now that the failure area and location are identified, an analysis and explanation will be done on
the type of failure.
After the test, pictures were taken of the compression panel. From these photos, combined with
the video of the test [8], the mode of failure can be determined.
In the beginning of the test , the plate stays intact (see Figure 6.2 [8]) up to a load of 28[kN ].
When looking at the video, one can see that from a load of approximately 28[kN ], column buckling
starts at the stringers, causing the whole panel’s top plate to "fold" in the middle (start of thin sheet
buckling), see also Figure 6.3 [8]. This column buckling increases the compression force on the inner side of the curvature (the panel’s top plate). Due to the increase in compression force on the
top plate, the critical buckling load of the plate is reached and the plate buckles permanently (fully
developed thin sheet buckling occurs).
Figure 6.2: The panel at the beginning of the test, it is not yet deformed. On the left side the side view of the panel can be
seen, on the right the front view of the panel. From: [8]
6.2. Description and Explanation of Failure Type
21
Figure 6.3: The panel at 28 [kN] loading, the first column buckling of the stringers has already taken place, now thin sheet
buckling of the top panel starts. On the left side the side view of the panel can be seen, on the right the front view of the
panel. Note the −28.7[kN ] indication on the bottom left. From: [8]
Then, at approximately 44[kN ], the whole panel fails to withstand the applied loads. The thin sheet
buckling of the top plate and the column buckling are at their maximum, see Figure 6.4 [8].
When the machine stops compressing at the end of the test, the stringers have a "spring-back" tendency and partially regain their original shape, whereas the top plate remains deformed, see Figure
6.5 [8]. This means that the stringers have not failed entirely, as it does not show complete plastic
deformation after the compression test. Therefore, it is likely that the panel could not withstand the
loads anymore due to top plate failure. It is thus concluded that the panel failed due to thin sheet
buckling of the top plate.
Figure 6.4: The panel at 44 kN (see bottom left indication): the thin sheet buckling is permanent and is visible on the right
side of the image. The stringer column buckling also reached its maximum (left side of the image). From: [8]
6.3. Comparison of Test Data with Failure Load/Mode Calculation
22
Figure 6.5: The panel after testing. Notice how the thin sheet buckling of the top plate (right side of the image) is
permanent and how the stringers experienced partial spring back (left side of the image) and have therefore not failed.
From: [8]
6.3. Comparison of Test Data with Failure Load/Mode Calculation
As expected, the results of the test show an underperformance of the real panel in comparison to
the theoretical one. The real loading mode and the manufacturing imperfections do not perfectly
match the theoretical conditions, which automatically led to an implicit error in the calculations.
Table 6.1: Requirements vs Calculated vs Testing results.
Parameter
Required
Calculated
Testing Results
Buckling Load [kN ]
Failure load [kN ]
34.5
40
41
44
28
45
As we can see in Table 6.1 the buckling occurred at a force of about 13[kN ] less than expected or
about 70% of the calculated buckling load. This does not satisfy the requirements given by the IAC,
as the requirements asked for buckling only after 34.5[kN ] [5]. This means that our safety factor
was not big enough to account for all the errors created by the assumptions made during the design process and the aforementioned real life conditions. According to our calculations, the stress
in the plate will reach the ultimate strength of the material at loading of around 61.5[kN ] which is
well above the maximum load achieved during the test and thus we have no information to confirm
neither deny this claim.
The failure mode for our compression panel was excessive buckling (mainly thin sheet and column
buckling), which was expected by the team. With calculated failure load just 1[kN ] off the predicted
one (well within the margin of error), it can safely be argued that the prognosis made before the
test was accurate to a quite high degree, at least concerning the failure load. An increase in the
thickness of some of the stringers should be able to combat the bucking load problems that the
panel encountered.
6.4. Assessment of the Production Quality in Relation to Testing Outcome
The production quality greatly affects the performance of the compression panel. The manufacturing method and the complexity of the design are mainly responsible for the production quality.
Since the manufacturing method of the compression panel is done by hand, the presence of manufacturing imperfections is likely. A slight displacement of a rivet can already cause in a change the
6.4. Assessment of the Production Quality in Relation to Testing Outcome
23
internal shear flow distribution and thus leading to an uneven shear concentration in the panel.
This can lead to the compression panel failing earlier than expected. An ideal compression panel
would fail in a straight horizontal line in the middle of the panel. As can be seen from the formula
for shear flow:
VQ
q=
(6.1)
I
Since Q is largest in the middle of the panel and the other variables do not change the shear flow will
be largest there and it is expected to fail at that location. Additionally during bending and buckling
normal stresses are created in the panel.
My
σ=
(6.2)
I
In this equation "y" and "I " stay constant, but "M " changes and is greatest in the middle of the
panel. From this it follows that normal stresses are most severe at the middle of the panel, which is
the other reason for an ideal plate to be failing there.
6.4.1. Visual analysis of riveting error
To register the locations and magnitudes of the imperfections in the production process of the
panel, a first-order visual analysis has been conducted. In this visual analysis the deviations from
the horizontal and vertical reference lines have been mapped out using photo-editing software to
indicate where to measure the most significant imperfections of rivet placement.
In Figure 6.6 and Figure E.1, the analysis of the whole panel is visible. A more detailed view of the
buckled section can be seen in Figure 6.7. In Figure 6.6, each horizontal row was given a letter from
top to bottom (A to L), and each vertical row a number from left to right (1 to 7). This gives each
rivet an unique letter-number combination. Next to that, the vertical green lines are the reference
lines. These lines start in the midpoint of the rivets in row "A" and end in the midpoint of the rivets
in row "L". The orange lines are also reference lines. These start at the lower edge of each rivet in
row 1 and end at the lower edge of each rivet in row 7. Like this, the deviation from the orange lines
is marked in yellow and the deviation from the green lines in blue. For a more detailed view of the
panel analysis and the locations of deviation see Appendix E.
Figure 6.6: Full panel analysis (own work).
6.4. Assessment of the Production Quality in Relation to Testing Outcome
(a) With Panel
24
(b) Without Panel
Figure 6.7: Close look at manufacturing error (own work).
6.4.2. Visual analysis limitations
This method is not a hundred percent accurate and merely a tool to make a first-order visualisation
to find the location of the errors on the compression panel.
The following limitations might have an influence on the outcome of the results:
• The visual analysis is done on the panel after the compression test, which permanently deformed the panel locally and thus might caused for particular dislocations of some rivets;
• The image used has a HD quality which has its limitations in accurately depicting the possible
dislocations;
• The picture was taken without a proper camera stand. This introduces a slight angle into the
picture influencing the accuracy of the grid;
• The boundary reference rivets could also have been placed in inaccurately, which results in
inaccurate reference lines;
• The grid was made by hand. This means that there could exist some imperfections in it.
6.4.3. Visual analysis results
The possible limitations discussed in Section 6.4.2 cause some uncertainty in the analysis. That is
why ’possible error’ was used instead of ’small error’. It is uncertain if these are actual errors, until
proper measurements have been made. The large errors are too big to be caused by the inaccuracy
of the analysis and can be used for further analysis. note that most large deviations are centered
around the same area, visible in figure 6.7 and Appendix E. This related to the local change of plastic
deformation.
As seen in Table 7.2, rivets G3 and E3 have the greatest imperfections. Coincidentally rivet G3 is also
in the middle section of the panel. This section experiences the most internal forces as stated in the
introduction of Section 6.4. Since the internal forces are highest here, this is also where the effects
of a imperfection are expected to be noticed first. There are also several other large imperfections in
the region left to rivet G3. The effect of the imperfections can be clearly seen in the pictures of the
tested panel. The panel yields in a horizontal line until rivet G3. After G3 the yield line moves down
a row.
6.4. Assessment of the Production Quality in Relation to Testing Outcome
25
Table 6.2: Rivet location deviation from theoretical design.
Row
Large error
Possible error
No error
A
B
C
D
E
F
G
H
I
J
K
L
7
2, 3, 4, 7
2, 7
2, 3, 7
3
5
-
2, 3
2, 4, 6, 7
2, 5, 6
5, 6
3, 4, 5
6
2, 3, 6
1, 2, 4, 5, 7
1, 4, 7
1, 2, 3
4, 5, 6
1, 4, 5, 6, 7
All
1, 3, 5
1, 3, 4
1
1, 6
1, 4, 5
1, 4, 5, 7
6
2, 3, 6
4, 5, 6, 7
1, 2, 3, 7
6.4.4. Measured results
For the rivets near the buckled parts of the plate and of which was estimated that they contained the
largest relative displacement error (using the visual analysis from Section 6.4.3, Table 6.3) the actual
production inaccuracy of the rivet placement was measured. The results can be found in Table 6.3.
Table 6.3: The measured inaccuracies of relative rivet placement.
Rivet
positive y [%]
negative y [%]
positive x [%]
negative x [%]
F2
G2
G3
F7
G7
8
0.0
8.1
1.5
2.5
0.0
2.5
0.0
1.5
5.5
-1
1
-2.5
3.5
2.5
0.0
0.0
2.5
-1.5
-2.5
There are a few remarks to be made with regard to this table:
• The measurements were taken after the panel test, meaning the panel had been deformed
and the measurements are thus a bit inaccurate;
• The measuring was done by hand. This introduces inaccuracy as well;
• A coordinate system has been set up to describe the position of one rivet relative to another.
These distances were measured with the "E10E"-inscription above and the "-0.95"-inscription
down (as in Figure 6.6). These distances are defined as follows: positive y (distance of rivet
relative to the rivet above), negative y (distance of rivet relative to the rivet below), positive x
(distance of rivet to the rivet on the left or the panel side, whichever is applicable) and negative x (distance of rivet to the rivet on the right side or the panel side, whichever is applicable).
A positive y value of for example 2 would indicate that the distance between the indicate rivet
and the rivet above is 2 percent larger than what it should have been according to the production plan (37[mm]).
Most likely, the small relative placement errors of especially rivets F2, G2 and G3 led to the characteristic horizontal S-shaped buckle between rows F, G and H, see Figure 6.6.
7
Conclusion and Recommendations
This project investigated the purpose and design process of a Launcher Compression Panel for the
G.E.O.R.G.E launcher from DELTA. The purpose of this project is to explain the function of the side
panels of a launcher and to design the panel itself. The ideal configuration for the panel involved
meeting desired strength at minimum weight possible.
The compression panels of a launcher experience compression forces due to the high amount of
thrust during lift-off. The function of the compression panels is to withstand these high compression forces without failing. For this project, a compression panel has been designed that was required to meet the following requirements:
• The panel must only buckle above 34.5[kN ];
• Failure of the panel must occur at 40[kN ];
• The panel design must be optimised for minimum weight.
By strengthening the panel with stiffeners riveted to the thin plate the design parameters in Table
7.1 have been concluded.
Table 7.1: Design Parameters
Design Parameter
Value
Face Sheet Thickness [mm]
Stringer Type [-]
Number of Stringers [-]
Stringer Spacing [mm]
Number of Rivets [-]
Rivet Spacing [mm]
0.8
L-3
7
57
12
38
After the design was made, the compression panel needed to be manufactured. For this, a production plan was written to instruct the manufacturer how the panel needed to be made. The manufactured panel was made mostly identical to the designed panel. However, small production mistakes
led to slightly different panel behaviour.
To check if the manufactured panel would meet the requirements, it was tested using a MTS 311.51
test system. This test system operates by clamping the compression panel and applying a compression force up to the point when the panel has compressed 30 mm or when the test system measures
a reaction force equal to 20% of the maximum compression the panel can support after it has failed.
The test has led to results which are compared to the calculated values for the design in Table 7.2.
26
27
Table 7.2: Calculated vs Testing results
Parameter
Required
Calculated
Testing Results
Buckling Load F [kN ]
Failure load [kN ]
34.5
40
41
44
28
45
The test results imply that the panel was capable of resisting column buckling at the stringers until a
load of approximately 28[kN ]. This is lower than the first requirement provided by the IAC. Furthermore, the panel failed to withstand the applied loads at a load of approximately 45[kN ]. This means
that the designed compression panel was almost successful in meeting the requirements provided
by the IAC as it did not quite meet the buckling load of 34.5[kN ].
By analyzing the obtained test results, it was pointed out that the panel failed due to thin sheet
buckling of the top plate, combined with a deteriorated load-carrying capacity of the stringers due
to column buckling. A possible cause for the earlier-than-expected buckling of the panel could lie
in the fact that small manufacturing errors were made, which was the case for a few rivets.
Recommendations
Due to the ultimate strength of the design not being reached in testing, further optimisations for
lower ultimate strength could be considered to allow a weight saving. Furthermore, different materials for the compression panel including the stringers can be investigated to determine whether
these materials will be more optimal for the design.
Bibliography
[1] T. Woinowsky-Krieger, Theory of Plates and Shells. McGraw-Hill, 2 ed., 1959.
[2] J. Wijker, Spacecraft Structures. Springer, 1 ed., 2008.
[3] L. Abbas, X. Rui, and P. Marzocca, “Aerothermoelastic analysis of panel flutter based on the absolute nodal coordinate formulation,” Multibody system dynamics, vol. 33, pp. 163–178, 2015.
[4] V. Dawson and M. Bowels, Taming Liquid Hydrogen: The Centaur Upper Stage Rocket 1958-2002.
NASA, 1 ed., 2004.
[5] TUDelft, “Compression panel reader,” 2021.
[6] “Astm e9 – compression testing of metals.” https://www.trl.com/astm_e9_compression_
testing_of_metals/. Accessed: 1-3-2021.
[7] M. Niu, Airframe Stress Analysis and Sizing. Hong Kong Conmilit Press LTD, 2 ed., 1999.
[8] E10E Panel Test Video. IAC Testing Department, 2021.
28
A
Gantt Chart
29
30
Work Done per Session
1
Writing introduction of production plan
Writing tools and materials list
Describing each manufacturing step
Writing time estimates
Making CATIA model
Making relevant technical drawings
Finishing production plan
Handing in production plan
Making first design
Writing chapter on design
Writing description of production plan
Doing post manufacture analysis
Updating production plan based on feedback
Describing test
Plotting Received Data
Writing test analysis method
Analyzing test and data
Analyzing production quality
Writing introduction of report
Writing conclusion and recommendations
Doing literature search
Editing and finishing
General formatting overleaf
Handing in design report and drawings
2
2.5
3
4
5
6
7
8
31
Activity
People
Writing introduction of production plan
Writing tools and materials list
Writing safety precautions
Writing steps for measuring and marking
Writing steps for layout and sizing
Writing steps for drilling and finishing
Writing steps for clamping and riveting
Making CATIA model
Making relevant technical drawings and renders
Checking production plan
Handing in production plan
Writing introduction of report
Doing literature search
Making first design
Writing chapter on design
Writing description of production plan
Doing post manufacture analysis
Updating production plan based on feedback
Describing test procedure
Describing test events
Plotting Received Data
Writing test analysis method
Analyzing test and data
Analyzing production quality
Writing conclusion and recommendations
Editing and finishing
General formatting overleaf
Handing in design report and drawings
Theophile, Lucas
Aleksei, Bart
Aleksei
Aleksei, Ewan
Mike, Theophile
Didier, Dragomir, Robin
Aleksei, Lucas, Morris
Dragomir, Bart, Aleksei
Time
spent
(min)
25
240
15
75
75
180
240
240
Dragomir, Aleksei
200
Bart, Aleksei
Robin
Theophile, Lucas
Lucas, Morris, Robin, Theophile
Didier, Ewan, Mike, Dragomir
Didier, Ewan, Mike, Bart
Robin
Mike, Didier, Ewan
Mike, Didier, Ewan, Dragomir
Lucas, Theophile
Lucas, Morris, Robin
Lucas, Morris, Dragomir, Robin
Lucas, Morris, Aleksei
Aleksei, Bart, Dragomir, Theophile, Lucas
Aleksei, Bart, Lucas
Didier, Ewan, Mike
Bart, Morris, Robin
Robin
Dragomir, Robin
105
15
35
240
240
240
60
60
180
15
60
180
200
200
180
90
120
240
15
Table A.1: The task division and time spent on each task
Session 2.5 in the Gantt chart indicates when we all worked on the production plan outside of
project hours for about an hour. For the rest every block corresponds to a planned session.
The time spent in Table A.1 is the time people spent on this task on average.
B
Production Plan
32
"This is the Production Plan in Appendix B"
Summary
For the manufacturing of components it is important to know what parts and tools are required and how
these parts must be assembled. This is the purpose of this production plan; to describe in clear steps
what the method of manufacturing is for a compression panel used in a rocket by the DELTA Company.
Without this clear description it is hard for a manufacturer to know the exacts of a manufacture. Other­
wise, the component might not end up as required. Calculations and technical drawings are made in
this report to ’freeze’ the design of the compression panel. Also, a list of materials, a list of tools and a
step­by­step procedure are given for the manufacturing of the panel.
i
"This is the Production Plan in Appendix B"
Contents
Summary
i
1 Introduction
1
2 Tools and Materials needed for Compression Panel Assembly
2.1 List of required Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 List of required Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.1 Tools for Measuring and Marking . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.2 Tools for Punching, Drilling and Finishing . . . . . . . . . . . . . . . . . . . . . . .
2.2.3 Tools for Clamping and Riveting . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
2
3
3
4
4
3 Manufacturing Steps needed for Compression Panel Assembly
3.1 Safety Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Steps for Measuring and Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.1 Marking the Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.2 Marking of the L­Stringer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Steps for Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4 Steps for Punching, Drilling and Finishing. . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.1 Deburring the Plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.2 Drilling the Plate and the Stringers . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.3 Finishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5 Steps for Clamping and Riveting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
5
5
5
6
7
8
8
8
9
9
Bibliography
10
A Technical Drawings
12
ii
"This is the Production Plan in Appendix B"
1
Introduction
In this report, a detailed production plan is given on how to manufacture a rocket side panel for the new
launch vehicle designed by DELTA: the GEOspace Rocket for Gravity (GEORGE). A launch vehicle
essentially is a tube with an engine and a fuel tank inside of it. To make sure the launcher is aerody­
namically shaped and protects its interior components, it needs a shell which maintains the cylindrical
shape of the rocket. This shell is composed of many smaller, reinforced panels. This report gives the
production plan of these panels.
The panels are composed of three main parts:
• The panel;
• The stringers;
• The rivets.
The panel is a relatively thin sheet of metal, in this case aluminium. The aluminium stringers act as
reinforcement to the panel, as the panel on its own cannot support all compression loads during use.
The stringers are long, L­shaped pieces of metal which are there to give extra support by increasing
the average thickness of the panel without increasing the weight of the panel as much as when the
thickness of the panel itself would be doubled or tripled, for example. The rivet is a headed bolt which
is passed through holes in two pieces of metal and is then deformed, keeping the two pieces together
firmly. In this case, rivets are used to assemble the plate and the stringers.
This plan will first detail the tools and materials used to build the panel as well as the manufacturing
methods to build the sample panel in Chapters 2 and 3 respectively. To finish off the plan, 2D drawings
of the panel will be displayed. This is done throughout the chapters and in Appendix A.
"When in doubt about the interpretation of the assembly procedure in Chapter 3, please refer
to the drawings in Appendix A!
1
"This is the Production Plan in Appendix B"
2
Tools and Materials needed for
Compression Panel Assembly
To manufacture the compression panel the materials and tools in the lists below are needed. The tools
and materials described below will be used in the assembly process that can be found in Chapter 3.
This list mostly comes from the project reader [1].
2.1. List of required Materials
• 1x Metal sheet
• 7x L­profile metal stringers
• 90x Rivets
The dimensions and material for the sheet and stringers are as specified in Table 2.1. Additionally,
table 2.1 contains specifications for the rivets. The specifications for the sheet, stinger and rivets were
obtained from [1, pg. 5­6]. The dimensions for the stringers are visually presented in Figure 2.1 (own
work). The dimensions for the metal sheet are shown in Figure 2.2 (own work).
Table 2.1: Dimensions of the required materials. From [1, pg. 5-6].
Sheet type
Dimensions [mm x mm]
Thickness [mm]
Material
F-1
400 x 495
0.8
Aluminium
L-profile stringer type
Dimensions [mm x mm]
Length [mm]
Material
L-3
15 x 15 x 1.5
495
Aluminium
Rivet Head Shape
Diameter Ø[mm]
Length [mm]
Material
Mushroom head
3.2
6
Steel
2
"This is the Production Plan in Appendix B"
2.2. List of required Tools
Figure 2.1: Dimensions of the stringer (own work)
Figure 2.2: Dimensions of the sheet (own work)
2.2. List of required Tools
2.2.1. Tools for Measuring and Marking
For measuring and marking, the following tools are required:
• Pencil;
• Permanent marker;
• Try square;
• Steel ruler;
• Tape measure .
3
"This is the Production Plan in Appendix B"
2.2. List of required Tools
2.2.2. Tools for Punching, Drilling and Finishing
For Punching, drilling and finishing, the following tools are required:
• Hearing protection;
• Safety glasses.
• Centre punch;
• Hammer;
• Drill bit Ø=2.5 [mm] (for the pre­drilling pilot­hole);
• Drill bit Ø=3.2 [mm] (for final drilling finish);
• Hand reamer (for plate deburring);
• Handheld counter sink (for hole deburring);
• File (for removing minor irregularities).
2.2.3. Tools for Clamping and Riveting
For clamping and riveting, the following tools are required:
• Clamp screw (for temporary clamping of stringers to the plate);
• 6x Rivet clamp Ø=2.5 [mm] (for temporarily fastening a hole after pre­drilling);
• 6x Rivet clamp Ø= 3.2 [mm] (for temporarily fastening a hole after final drilling);
• Hand riveter.
4
"This is the Production Plan in Appendix B"
3
Manufacturing Steps needed for
Compression Panel Assembly
To manufacture the compression panel correctly, the manufacturing steps listed below apply. The list
is derived from the project reader [1] and the available videos [2] and [3].
3.1. Safety Precautions
Before starting manufacturing, make sure to follow the following safety measurements:
1. Adhere to all COVID­19 regulations that are applicable during the session;
2. Wear safety glasses at all times during manufacturing;
3. Abide by all safety rules.
3.2. Steps for Measuring and Marking
The first step of manufacturing is to mark the right dimensions on the aluminium panel and L­stringers
as shown in Figure 3.1.
3.2.1. Marking the Panel
(Time Estimate: 10 min.)
1. Put the pre­cut F­1 aluminium panel (0.8 [mm] thickness) horizontally on a workbench;
2. To mark the locations of the centre lines for the lines of rivets for the stringers on the aluminium
panel, mark a point on the short edge of the panel 29 [mm] from the long edge. Continue marking
points at a spacing of 57 [mm] until there are 7 points. Use a set square to mark lines from these
points to the opposite edge of the panel;
3. Repeat Step 2 for the opposite end of the panel.
5
"This is the Production Plan in Appendix B"
3.2. Steps for Measuring and Marking
6
Figure 3.1: Dimensions for rivet holes on sheet F-1 (own work)
3.2.2. Marking of the L­Stringer
(Time Estimate: 10 min.)
1. Put all 7, unmodified, type L­3, aluminium stringers (with a length of 495 [mm]) horizontally on a
workbench;
2. Mark the centre line on one face down the long side of one stringer (7 [mm] from the long, unbent,
edge), using a set square;
3. Along the centre line mark a point 44 [mm] from the bottom from the stringer. Repeat the point
with spacing 37 [mm] until there is 12 marks, no marks should be present closer than 35 [mm] to
the upper or lower edge;
4. Repeat this procedure for the other six stringers;
Figure 3.2: Dimensions for rivet holes on the Stringer (own work)
"This is the Production Plan in Appendix B"
3.3. Steps for Layout
7
3.3. Steps for Layout
(Time Estimate: 5 min.)
1. Place the Stringer centre line aligned with the two marked points on the opposite ends of the
panel;
2. Repeat Step 1 for each of the 7 stringers;
3. The edge stringers should be 29 [mm] ±1 [mm] away from the nearest long side of the aluminum
sheet;
4. Ensure that the L­direction of the stringers is consistent, i.e. the L­sides of the stringers are
oriented the same way.
5. Clamp all the stringers in place in preparation for drilling. To do that you need to use the clamp
screws to fix the stringer and the plate together at both ends of the stringer as shown in Figure
3.4. Place them together in the position that they will eventually be secured in;
The final lay­out of the panel (ignoring the rivets) should be as depicted in 3.3
Figure 3.3: Lay-out of Compression Panel (own work)
"This is the Production Plan in Appendix B"
3.4. Steps for Punching, Drilling and Finishing
(a) Clamping Method front view
8
(b) Clamping Method side view
Figure 3.4: Clamping method (own work)
3.4. Steps for Punching, Drilling and Finishing
"Warning: use sacrificial metal plates during the following steps to protect the workbench from being
damaged especially during drilling.
3.4.1. Deburring the Plate
(Time Estimate: 5 min.)
Before starting the drilling process, the burrs on the edges of the plate created during the cutting process
need to be removed.
1. Remove the burrs on the edges of the plate using a hand reamer. This is done by first positioning
the hook­end of the hand reamer against the plate edge;
2. Pull the hand reamer along the plate edge with one firm motion;
3. Repeat this process for every burred plate edge.
Now the holes for the rivets need to be drilled. This will be done by drilling the holes through the
stringers and the plate at the same time.
3.4.2. Drilling the Plate and the Stringers
(Time Estimate: 30 min.)
1. Grab the hammer and the centre punch and use it to make small indents at all the places pre­
viously marked for drilling on the stringer. One can do this by holding the centre punch upright
over the mark with the sharp end being placed right on top of it and then hammering the centre
punch softly at the flat end. Those indents will be used as a lead for drilling the holes;
2. Drill a pilot hole straight down through both the plate and the stringer at the same time at the
location where each indent was made using the 2.5 [mm] drill bit. Begin with one of the holes
at the center of the stringer to prevent clamp slippage. After drilling every hole a 2.5 [mm] rivet
clamp can be used to secure the plate and stringers together preventing further slippage. To drill
the holes, the drill needs to spin clockwise at the highest power setting. Remove all the rivet
clamps once you are done with drilling the pilot holes;
3. Finish these holes by drilling straight down through the pilot holes using a 3.2 [mm] drill bit. Here
the 3.2 [mm] rivet clamps can be used in the same capacity as the 2.5 [mm] ones in Step 2.
Again, to drill the hole the drill needs to spin clockwise at the highest power setting.
4. Repeat Steps 1 ­ 3 for all holes in all 7 stringers.
"This is the Production Plan in Appendix B"
3.5. Steps for Clamping and Riveting
9
Now that the holes are made, the burrs created during the process need to be removed.
3.4.3. Finishing
(Time Estimate: 20 min.)
1. Use the counter sink tool to remove the burrs from the holes in the plate and the stringers. To do
this, start by putting the sharp end of counter sink tool into the hole on each burred side;
2. Turn the counter sink tool clockwise around its own axis while pushing it into the hole until the
burr is removed;
3. Repeat Step 1 and Step 2 for every hole made in the plate and the stringers;
4. Remove the remaining burrs on the edges of the stringers using a file by holding the file against
the edge and move it back and forth using long strokes until the edge is smooth;
5. Repeat Step 4 for all the burred edges of the stringers;
6. If any other work piece material remains either on the plate or the stringers, use the file to remove
it using the same motion as described in Step 4. If there is no remaining work piece material, this
step can be skipped.
3.5. Steps for Clamping and Riveting
(Time Estimate: 30 min.)
Figure 3.5: Riveting Setup (own work)
1. Align the L­stringer with the drilled holes from 3.4;
2. Fasten the L­stringer to the panel using rivet clamps by putting them through the pre­drilled holes
that are oriented with the L­stringer’s pre­drilled holes;
3. Mount the nose piece onto the rivet gun that can fit rivets of 3.2 [mm] in diameter;
4. Connect the pneumatic rivet gun to an air supply unit and turn the unit on;
5. Insert a blind rivet into every hole, from the stringer side, that does not have a rivet clamp in it
from the side of the panel. Make sure the mandrel of the rivet sticks out like in Figure 3.5;
6. Put the rivet gun on one of the rivets, squeeze the gun down tightly and push the trigger to rivet
it;
7. Repeat this for the other rivets;
8. Remove the rivet clamps and rivet the non­riveted holes;
"This is the Production Plan in Appendix B"
3.5. Steps for Clamping and Riveting
10
9. When all the holes without rivet clamps have been riveted, take out a rivet clamp and rivet that
hole. Repeat this until all the rivet clamps are gone and all the holes have been riveted;
10. Now repeat Step 1 through 9 of this Section 3.5 until all 7 L­stringers have been riveted to the
panel. The compression panel is now ready for further assembly into the launch vehicle.
"This is the Production Plan in Appendix B"
Bibliography
[1]
TU Delft. “AE1222-I Design and Construction Project Manual Part II-Launcher Compression Panel
Design”. 2020.
[2]
TU Delft. AE1222-II Design and Construction: How to Use a Drill. Film. TU Delft. URL: https:
//brightspace.tudelft.nl/d2l/le/content/292963/fullscreen/2089219/View.
[3]
TU Delft. AE1222-II Design and Construction: Tools and Assembly Tips. Film. TU Delft. URL:
https://brightspace.tudelft.nl/d2l/le/content/292963/fullscreen/2089204/
View.
11
"This is the Production Plan in Appendix B"
A
Technical Drawings
12
"This is the Production Plan in Appendix B"
13
Figure A.1: Technical Drawing of the Stiffener. (own work)
"This is the Production Plan in Appendix B"
14
Figure A.2: Technical Drawing of the Sheet. (own work)
"This is the Production Plan in Appendix B"
15
Figure A.3: Assembly Drawing of the Compression Panel. (own work)
C
Aluminium properties
The properties of aluminium are (according to the project reader [5]):
Table C.1: The properties of aluminium. From [5]
σul t [M P a]
σ y [M P a]
E [M P a]
ρ [g /cm 3 ]
127
100
63500
2.78
50
D
Rivet properties
In the following table from the project reader [5] the rivet properties can be found.
Table D.1: Available rivet properties. From: [5]
Parameter
Value
Diameter [mm]
Length [mm]
Grip range [mm]
Head shape
Material body/mandrel
Shear load [N]
Tensile load [N]
3.2
6
3.0-4.6
Mushroom head
Steel
1060
1285
51
E
Panel Analysis Image
52
53
Figure E.1: Full panel analysis(without panel).
54
Figure E.2: Full panel analysis (own work).