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Strategien für das Maßschneidern von Faserverbundstrukturen in der Luft- und Raumfahrt
Strategies for the design of CFRP structures in aerospace and space applications
Prof. Richard Degenhardt2,3, Prof. Axel Hermann1,Dr. Andreas Baar1
1CFK-Valley, Stade2DLR, Institut für Faserverbundleichtbau und Adaptronik 3Private Fachhochschule Göttingen (Standort Stade)
2
1. Introduction
2. Example 1 (Space):
Future design concept for unstiffened CFRP structures
3. Example 2 (Aerospace):
Exploitation of reserve capacities in the postbuckling area of CFRP fuselage panels
4. Private University of Applied Sciences Göttingen
5. CFK-Valley Stade
Overview
3
Examples for future structures made of CFRP
Transport / Energy
Space
Ariane 5 Int. space station ISS
Aerospace
4
Year
CFR
P
787 = 50%
A380 = 22%
Source: NASA, Airbus und Boeing
Composite structures in aerospace
A350 > 50%
5
1. Introduction
2. Example 1 (Space):
Future design concept for unstiffened CFRP structures
3. Example 2 (Aerospace):
Exploitation of reserve capacities in the postbuckling area of CFRP fuselage panels
4. Private University of Applied Sciences Göttingen
5. CFK-Valley Stade
Overview
Ariane 5 Int. space station ISS
6
Task: Maximal buckling load for 2 double layers
R = 250 mm
L = 510 mm
t1 = t2 = 0,25 mm
Fmax = 31,39 kN
Fmin = 17,59 kN
Optimisation of an unstiffened CFRP cylinderunder axial loading
7
Future design concept for unstiffened CFRP structures
Guideline NASA-SP 8007 based on empirical methodsvery conservative knock-down factorsNo guidelines for composite structures
State of art
8
Radial perturbation load
Position and magnitude are variableSeveral tests with different imperfections
Test procedure:1. radial perturbation load2. axial compression
Future design concept for unstiffened CFRP structures
9
0
5
10
15
20
25
0 2 4 6 8 10
Perturbation load P (N)
Buc
klin
g lo
ad N
(kN
)
0
10
20
0 0,1 0,2 0,3
Displacement (mm)
Load
(kN
)
Test results for cylinder Z07 and one perturbation position
Future design concept for unstiffened CFRP structures
10
0
5
10
15
20
25
0 2 4 6 8 10Perturbation load P (N)
Buc
klin
g lo
ad N
(kN
)
0
10
20
0 0,1 0,2 0,3
Displacement (mm)
Load
(kN
)
Test results for cylinder Z07 and one perturbation position
Each dot marks one testUnexpected horizontal curve progression
Future design concept for unstiffened CFRP structures
11
0
5
10
15
20
25
0 2 4 6 8 10Perturbation load P (N)
Buc
klin
g lo
ad N
(kN
)
P1
N1
N0line (a)
line (b)
line (c)
Test results for cylinder Z07 and one perturbation position
New approach:Idealization of curve progression by three linesLower boundary limit of buckling load for imperfect shells:„Load carrying capability N1“
Future design concept for unstiffened CFRP structures
12
Evaluation of the Knock-Down Factor
500
Classical Buckling Load
Measured Buckling Loads
ρ
0.32
0.650.5% Quantile
NASA
Project cylinder propertiesTotal length = 540 mmFree length = 500 mmRadius = 250 mmPly orientation = +24,-24,+41,-41Thickness = 0.5 mm
MCS Simulations
Buckling Load with Single Perturbation Load
13
Summary / Conclusions
The NASA SP 8007 guideline is very conservative if composite structures shall be designed.The Single-Pertubation load approach is a promissing alternative.The knowledge of the minimum pertubation is needed.A new empirical formula for the critical pertubation load P1, which is a good assumption for the minimum pertubation load, was developed. This formula was in a first step developed for metallic structures.In future work it will be extended for composite materials.
5.10 ≤< t
14
1. Introduction
2. Example 1 (Space):
Future design concept for unstiffened CFRP structures
3. Example 2 (Aerospace):
Exploitation of reserve capacities in the postbuckling area of CFRP fuselage panels
4. Private University of Applied Sciences Göttingen
5. CFK-Valley Stade
Overview
15
Next generation –All composite fuselage structure
The current research considers curvedCFRP panels which are understood as parts of a fuselage section.
Structures considered
16
Scale factor: 10
Scale factor: 8
Scale factor: 5
Scale factor: 3
1st global (stringer-based) buckling
1st local buckling
Scale factor: 5
Shortening
Load
Real curve
Collapse load
Simplified curve
What is collapse(Example: Axially compressed curved stiffened CFRP panel)
17
FBL
Collapse
OD
I
II
III
Shortening
Load
UL
LL
Future Design Scenario
Design Scenarios for Stiffened Panels
Ultimate Load (UL)
First Buckling Load (FBL)Limit Load (LL)
Collapse
Onset ofDegradation (OD)
I
II
III
Allowed underoperating flightconditions
Safety Region
Not allowed
Shortening
Load
Current Design Scenario
18
WP 1 Benchmarking - Example
0
20
40
60
80
100
120
140
0 0.5 1 1.5 2 2.5 3 3.5 4Shortening [mm]
Load
[kN]
Experiment P12Abaqus, Nominal, No ImperfectionsSOL 106, Compdat, No ImperfectionsSOL 106, Compdat, With ImperfectionsSOL 600, Compdat, No ImperfectionsLS-Dyna, Compdat, No Imperfections
Not correct because 1) Degradation is not considered2) Sensitive for modelling of the lateral boundary conditions
Collapse
19
0
20
40
60
80
100
120
0 0,5 1 1,5 2 2,5 3 3,5
Shortening [mm]
Load
[kN
]
Cycle 0001Cycle 0401Cycle 0801Cycle 1201Cycle 1601Cycle 2001Cycle 2401Cycle 2601Cycle 2801Cycle 3001Cycle 3201Cycle 3401Cycle 3601Cycle 3801 Collapse
WP 4 - Test Panel P29 – Load shortening curve with Thermography
20
Analysis
Fast toolsTools with analytical and semi-
analytical approach
For design process For certification
Slow toolsCommercial FE tools (e.g.
SAMCEF, NASTRAN, ABAQUS ,etc.)
Simulation Tools
21
0
20
40
60
80
100
120
140
0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0Shortening [mm]
Load
[kN
]
ABAQUS - No degradation
ABAQUS - With skin-stringer separation
Test results
Comparison Simulation - Test
22
1. Introduction
2. Example 1 (Space):
Future design concept for unstiffened CFRP structures
3. Example 2 (Aerospace):
Exploitation of reserve capacities in the postbuckling area of CFRP fuselage panels
4. Private University of Applied Sciences Göttingen
5. CFK-Valley Stade
Overview
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