Future challenges in the design of structures made of CFRP Workshop presentatio… · Future challenges in the design of structures made of CFRP ... TransportTransport EnergyEnergy

Future challenges in the design of structures made of CFRP

Richard Degenhardt, Martin Wiedemann

DLR, Institute of Composite Structures and Adaptive Systems, Germany

ICAS Workshop, 5 September 2011, Stockholm

Institute of Composites Structures and Adaptive Systems

DLR Institute of Structures and Design, Institute of Materials ResearchInstitute of Composite Structures and Adaptive Systems

Example 1 (Space):Proposal for a new design concept of unstiffened CFRP structures

Example 2 (Aeronautics):Exploitation of reserve capacities of stiffened CFRP in the postbuckling area

Content

Ariane 5 Int. space station ISS


DLRGerman Aerospace Center

Research InstitutionSpace AgencyProject Management Agency


Locations and employees

7000 employees across 31 research institutes and facilities at

15 sites.

Offices in Brussels, Paris, Singapore and Washington. Koeln

Oberpfaffenhofen

Braunschweig

Goettingen

Berlin

Bonn

Neustrelitz

Weilheim

Bremen Trauen

Dortmund

Lampoldshausen

Hamburg

Stuttgart


Aeronautical Research at the DLR

Politik

Flight Physics

ATM &Airports

Air TransportConcepts

Engine

AircraftStructures

Weather &Climate

Systems& Cabins

Aerodynamic Systems and Flight Guidance, Virtual Aircraft

and new ConfigurationsFlexible Aircraft

Virtual Engines Propulsion Techniques

Turbines, Fans, Combustion Technology,

ValidationAir Transport ManagementHuman FactorsAirport Security

Low emission Noise impact, Wake vortex

Efficient airport traffic

Materials, Structures,Simulation and Validiation

Rotorcraft

DLR-Research Program


Research Institutes I


Research Areas

Institute of Composites Structures and Adaptive Systems 8

Our Profile

We are experts for the design and realization of innovative lightweight systems.Our research serves the improvement of:

• Safety• Cost efficiency• Functionality• Comfort• Environmental protection

Institute of Composite Structures and Adaptive Systems

Director: Prof. Dr.-Ing. M. Wiedemann


Our Professional Competences in theInstitute of Composite Structuresand Adaptive Systems

Our Professional Competences


We orient ourselves along the entire process chain for building adaptable, efficient manufactured, lightweight structures.

For excellent results in the basic research and industrial application.

CompositetechnologyCompositetechnology

AdaptronicsAdaptronics Composite Process

Technology

Composite Process

Technology

CompositedesignCompositedesign

Our Professional Competences – Bricks of theProcess Chain of High Performance Lightweight Structures


The The aimaim: : adaptable, tolerant, adaptable, tolerant, efficient manufactured, efficient manufactured, lightweight structureslightweight structures

StructuralmechanicsStructuralmechanics

Multifunctionalmaterials



Our Fields of Research

Our Fields of Reseach

Upstream ResearchBasic resarch

AeronauticsAeronautics SpaceSpace

TransportTransport EnergyEnergy

Downstream ResearchApplication related research

Our research and development on material systems and lightweight structures aims atSafety • cost efficiency • functionality • comfort • environment protection

Hig

h Pe

rfor

man

ce L

ight

Wei

ghtS

truc

ture

s

CompositetechnologyCompositetechnology

AdaptronicsAdaptronics Processtechnology

Processtechnology

CompositedesignCompositedesign

Structural mechanicsStructural mechanics




Multifunctional MaterialsDr. P. Wierach

Structural MechanicsDr. A. Kling

Composite DesignDr. C. Hühne

• Fiber- and nanocomposites• Smart materials• Structural health monitoring • Material characterization

• Global design methods• Stability and damage tolerance • Structural dynamics• Thermal analysis• Multi-scale analysis• Process simulation

• Design and Sizing• Structure concepts and

assessment• Multi-functional structures• Shape-variable structures• Hybrid structures

From materials to intelligent composites

From requirements via concepts to multi-functional structures

From the phenomenon via modeling to simulation


Our design for your structures!With high fidelity to virtual reality for the entire life cycle!We increase the ability of the materials!


Composite TechnologyDr. M. Kleineberg

AdaptronicsDr. H. P. Monner

Composite ProcessTechnologyDr. M. Meyer

• New technologies for manufacturing

• Hybrid manufacturing• Assembly• Repair• Process automation

• Automated FP und TL

• Online QA within Autoclaves

• Automated Manufacturing for mass-production

• Simulation methods for maximum process reliability und process assessment

From the idea via processes to prototypes

For sustainable processesFrom functional composites to adaptive systems

• Simulation and demonstration of adaptive systems

• Active vibration control• Active noise control• Active shape control• Autarkic Systems

Tailored Manufacturing Concepts Research with industrial dimension


The adaptronics pionieers in Europe!










• Fuselage design• Large cut-outs• Manufacturing technologies

• Savety relevant aeronauticstructures and UAVs

• Multifunctional compositestructures

• Demonstration of design and technology

• Flexible leading edge• Morphing of high lift systems• Structural integration of active flow

control

Our Fields of Research | Applied Research

FocusHigh Lift | M. Kintscher

Applied Research | Our Foci of Product Oriented Research

FocusFuselage Technologies | T. Ströhlein

FocusSpecial structures | M. Hanke


• Lander structures• Deployable space structures• Upper stage

• Next generation train• Novel vehicle structures

Our Fields of Research | Applied Research

FocusTransport | J. Nickel

FocusSpace | Ch. Arlt

In order to deal with strength, stability and thermo-mechanical problems we operate unique experimental facilities like thermo-mechanical test facilities, buckling facilities with the special feature of dynamic loading. Manufacturing facilities like preforming, filament winding, liquid composite moulding or microwave curing enable us to develop novel manufacturing techniques und the realization of innovative composite structures.

We transfer our scientific and technical expertise in the field of design and manufacture of lightweight composite structures and adaptronics as partners in an international network of research and industry.





Content



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

Collapse load

Scale factor: 10Scale factor: 10






1st local buckling1st local buckling

Scale factor: 5Scale factor: 5Scale factor: 5

Shortening

Load

Collapse loadCollapse load

Simplified curveSimplified curveSimplified curve0

10

20

0 0,1 0,2 0,3

Displacement (mm)

Load

(kN

)

Comparison: Stiffened and unstiffened structures

Light weight structures endangered by buckling can be divided into the following two groups:

Imperfection tolerant structures: Imperfection sensitive structures:

Maximum load > first buckling load Postbuckling area is exploited for designDesign load independent of imperfections

Maximum load = first buckling load No exploitable postbuckling areaDesign load highly dependent of imperfections

Stiffened panel

Unstiffened cylinder


Valid for metallic structuresNo guidelines for composites structures

Radius / Thickness

Kno

ck d

own

fact

or

Buckling load of the perfect cylinder, scaled to 1

State-of-the-art - NASA-SP 8007 Design guideline


Radius / Thickness

Kno

ck d

own

fact

or


FDesign load = FPerfect * r NASA

FDesign load = 32 * 0.32 = 10.2 kN

500

0.32

NASA-SP 8007 - Example

Example: CFRP cylinderTotal length = 540 mmFree length = 500 mmPly orientation = +24,-24,+41,-41 Radius = 250 mmThickness = 0.5 mmR/t = 500FPerfect = 32 kN


Radius / Thickness

Kno

ck d

own

fact

or



FDesign load = 32 * 0.32 = 10.2 kN

500

0.32



Experiments


Radial perturbation load

Position and magnitude are variableSeveral tests with different imperfections

Test procedure:1. radial perturbation load2. axial compression

Single Perturbation Load Concept (SPLC)



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

)


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

)

Each dot marks one testUnexpected horizontal curve progression



New approach:Idealization of curveLower boundary limit of bucklingload for imperfect shells:„Load carrying capability F1“

0

5

10

15

20

25


Buck

ling

load

N (k

N)

P1

N1

N0line (a)

line (b)

line (c)

Perturbation load P (F)

F1

F0

Buc

klin

g lo

ad F

P1 = Minimum single perturbation load



Questions

What are the limits of the single perturbation concept? Especially with respect to different kinds of structures.What is the minimum required single perturbation load P1 which is needed for the calculation?Are there any cases the single perturbation load is not leading to the worst imperfection?Applicable to stiffened structures?What kind of influence damages or holes will have on the buckling load?How does one model the structure in order to achieve reliable results?How broad is the bandwidth determined by stochastic approach?

0

5

10

15

20

25


Buc

klin

g lo

ad N

(kN

)

P1

N1

N0line (a)

line (b)

line (c)

Perturbation load P (F)

F1

F0

Buc

klin

g lo

ad F


Radius / Thickness



FDesign load = 32 * 0.32 = 10.2 kN

500

0.32


Experiments

Buckling load with the Single Pertubation Load Concept

0.58

FDesign load = FPerfect * r SPLC

FDesign load = 32 * 0.58 = 18.5 kN



Radius / Thickness


500

0.32


Experiments

Buckling load with the Single Pertubation Load Concept

0.58

Conclusion: The SPLC allows in this example to increase the load

carrying capacity by 82 %.



Next step:

EU project DESICOS (2012 - 2014)


The NASA SP 8007 guideline is very conservative if composite structures shall be designed.The Single-Perturbation load approach is a promising alternative.However, a lot of new questions are not answered (e.g. minimum perturbation load).First steps were performed (e.g. a new empirical formula for thecritical perturbation load P1 for metallics).

Summary and Conclusions





Content



Dynamics in Aircraft Engineering Design and Analysis forLight Optimized Structures

EU projects

More AffordableAircraft Structure through

eXtended,Integrated, &Mature

nUmerical Sizing

2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

COCOMAT (FP 6, STREP)

MAAXIMUS (FP 7, Level 2)

DAEDALOS (FP 7, Level 1)

Improved MATerial Exploitation at Safe Design of COmposite Airframe Structures

by Accurate Simulation of COllapse


FBL

Collapse

OD

I

II

III

Shortening

Load

UL

LL

Future Design Scenario

COCOMAT: Designs on panel level

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


Virtual PlatformInnovative & Integrated

Simulation-Based Design

Physical PlatformFull-scale Composite Fuselage

Manufacturing, Assembly & Test of 2 one-shot sections

Fast Development & Right-First Time Validation of a highly-optimized New Generation Composite Fuselage by a huge step in Simulation-based design

Development of two platforms

MAAXIMUS project– Strategy


Future work should facilitate full applicability of analysis methodsin preliminary design.

Speed of postbuckling analysis of stiffened panels needs to beincreased.

For collapse simulation degradation must be taken into account.

Conclusions and perspective


Thank you for your attention

Documents

Future challenges in the design of structures made of CFRP Workshop presentatio… · Future challenges in the design of structures made of CFRP ... TransportTransport EnergyEnergy