2nd int. conference on buckling and postbuckling behaviour ......buckling and postbuckling behaviour...

Institut für Faserverbundleichtbau und Adaptronik

Improved Material Exploitation of Composite Airframe Structures by Accurate Simulation of Collapse –

The COCOMAT project

2nd Int. Conference on

Buckling and Postbuckling Behaviour of Composite Laminated Shell Structures

R. Degenhardt, D. Wilckens, K. Rohwer, R. Zimmermann, J. Teßmer3 -5 September 2008, Braunschweig, Germany

2Institute of Composite Structures and Adaptive Systems

Outline

1. The EC 6th Framework Programme

2. Forerunner projects (interaction, results)

3. Consortium

4. Structures considered, what is collapse

5. Overall objective, kind of degradation, main results

6. Examples of results

7. Summary


The EC 6th Framework ProgrammeIntegrating and strengthening the European Research Area

Priority 4: Aeronautics and Space

Work Programme:

Area: Strengthening competitiveness

Objective: Reduction of aircraft development and operating costs by 20% and 50% in the short and long term, respectively.

The EC 6th Framework ProgrammeIntegrating and strengthening the European Research Area

COCOMAT contributes to this aim by:

Instrument: Specific Targeted REsearch Project (STREP)

Goal: Reducing structural weight at safe design by exploitation of considerable reserves in primary fibre composite fuselage structures through accurate simulation of collapse


ImprovedPOstbuckling

SImulation for Design of FibreCOmposite

Stiffened FuselageStructures

Improved MATerial Exploitation at Safe Design of COmposite Airframe Structures

by Accurate Simulation of COllapse

Forerunner projects - Interaction

Year

GARTEUR AG 25

POSICOSS

COCOMAT

2000 2001 2006 200720052002 2003 2004

Group for Aeronautical Research and Technology in EURopeAction Group 25:Postbuckling and Collapse Analysis


ConsortiumCOCOMAT Consortium

SMEs Research establishments UniversitiesLarge

industries

PL

IL

E

B

AUS

D

I

GR

D

SS IL

CH

I

D

LV


Next generation –All composite fuselage structure

COCOMAT considers curved CFRP panelswhich are understood as parts of a fuselage section.

Structures considered


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)


degradation (OD)

Current design scenario

Shortening

Not allowed

Safety region

Load

I

II

III

First Buckling Load (1. BL)

Collapse (CL)

Ultimate Load (UL)

Limit Load (LL)

Onset of

Allowed under operating flight conditions

LoadFuture design scenario

1. BL

CL

UL

LL

OD

Shortening

III

I

II

COCOMAT – Main objective (1)


Fast and accurate simulation of the collapse load of

stringer stiffened CFRP curved panels with taking

degradation and cyclic loading into account, in addition to

geometrical nonlinearity.

cyclic loading = repeated static loading

COCOMAT – Main objective (2)


Failure propagation will be taken into account

Skin-stringer separation is considered as the most important and dangerous mode and is investigated in any case.

Delamination in the stringer blade was also observed in the POSICOSS project and is considered.

Delamination in the skin is be considered as less important case, however, is also taken into account.

Kind of degradation


Work plan

WP 1: Benchmarking on collapse analysis of undamaged and damaged structures with existing tools

WP 2: Material characterisation, damage investigationand design of structures for static and cyclic tests

WP 3: Development of improved simulation proceduresfor collapse

WP 4: Manufacture, inspection and testing by static and cyclic loading of undamaged panels from WP2

WP 5: Manufacture, inspection and testing by static and cyclic loading of pre-damaged panels from WP2

WP 6: Design guidelines and industrial validation

WP 7: Management and exploitation

Year 200820072004 2005 2006


Experimental data base Slow certification tools and fast design tools

Mai

n re

sults

Mai

n ob

ject

ive

C O C O M A T

Design guidelines

Future design scenario

COCOMAT – Main results

Personnel resources: 716 person-monthsTotal costs: 6.7 Mio EurosEC funding: 4.0 Mio Euros

Some details:


pre-damagedpanelsWP 5

Validation of the improved

tools

undamagedpanels Manufacture,

inspection and testing by static and cyclic loading of

WP 4

Degradation models for

the improvedtools

Investigation of degradation by tests and development of degradation models

WP 2.2

Material properties

Characterisation of material propertiesWP 2.1

ObjectiveKind of structureWorkpakage

Panels

Stiffened strips

SpecimensGFRP layer

Experimental data base


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


Outline

1. The EC 6th Framework Programme

2. Forerunner projects (interaction, results)

3. Consortium

4. Structures considered, what is collapse

5. Overall objective, kind of degradation, main results

6. Examples of results

7. Summary and conclusions


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


WP 2 - Material properties, degradation models and panel designs

Material properties: - IM7/8552 UD- 985-GT6-135 UD- 950-GF3-5H-1000 carbon fabric

Degradation models (experiments and mechanical models)Designed panels which should be manufactured and tested(85 designed, 6 selected)


WP 3 - Improved simulation procedures for collapse -Slow certification tools

Commercial software'sIn-house software's

ABAQUS

MARC

NASTRAN

FEAP

SAMCEF

STRIPE

Stress based

Fracture based

Degradation models

Tsai Hill, Maximum stress, Minimum strain, Puck

VCCT energy release rates


WP 3 - Improved simulation procedures for collapse -Fast design tools

Seconds Minutes Hours Days

Full FEM

Computing Time

Prec

isio

n

DLR

RTUTraining

RWTH

TECHNION

RTUFast tool

SMR UKA


WP 4 / WP 5 Buckling tests until collapse


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


0

20

40

60

80

100

120

0 0,5 1 1,5 2 2,5 3 3,5

Shortening [mm]

Load

[kN

]

1

2

3

4

5

6

WP 4 - Panel P29 – Load shortening curve


WP 4 – Panel P29 – Measurements after collapse

ARAMIS Ultrasonic inspectionThermography1

1In co-operation with Institut für Kunststoffprüfung und Kunststoffkunde Universität Stuttgart


WP 5 – Test Results TECHNION


Comparison Test and Simulation

Selcected highlights

Institute of Composite Structures and Adaptive Systems

• A 1D-element with adhesive layer, linear softening model and a mixed mode fracture criterion has been developed

• The approach was validated with simulations of DCB, ENF and MMB tests

Comparison of test results and simulations MMB test

• A 1D-element with adhesive layer, linear softening model and a mixed mode fracture criterion has been developed

• The approach was validated with simulations of DCB, ENF and MMB tests

Comparison of test results and simulations MMB test

Partner: RWTH


Highlights

Rib-Stiffened DCB Test

Small-Scale PanelsSmall-Scale Panels Large-Scale Panels

Rib-Stiffened 3PB Test

FE tool for composites:• Delamination / skin-stringer separation:

Cohesive interface elements

• Ply failure: Shell elements with Tsai-Wu or Hashin criteria (optional) and ply discountmodel for degradation

• Applicability proven by various simulations

0

10

20

30

40

50

60

70

0 5 10 15 20Crack Opening [mm]

App

lied

Load

[N]

DCB Test

Partner: University of Karlsruhe


Partner: CRC-ACS

Aernnova panel (D2), comparison with intact panel test1-2

fibre failure

D2 intact panelFE analysisDebond prediction

520

260

1.92 mm axial compression

Experiment Numerical

ExperimentNumerical

Experiment Numerical

0 0.5 1.0 1.5 2.0 2.5 3.0

250

200

150

100

50

0

Load

[kN

]

Displacement [mm]

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5Displacement [mm]

120

100

80

60

40

20

0Lo

ad [k

N]

1) Orifici, A.C. et al., Composites 2007, Porto, Portugal, 12-14 Sep., 2007.2) Orifici, A.C. et al., Composite Structures, 86: 186-193, 2008.

DLR panel (D1), comparison with panel after cyclic loading (producing pre-damage)1


Partner: SMR

Improved post-buckling analysis of composite with the B2000++ finite element simulation environment

New fast and robust family of shell elements with finite rotation with 5 or 6 degrees of freedom and pre-integration of the material equations, Assumed Natural Strain and Enhanced Assumed Strain to reduce locking.New parallel static and dynamic non-linear FEM solvers.

Dynamic post-bucking analysis of industrial panel


Partner: RTUDCB test for rib stiffened panel

Ultrasonic inspection of COCOMAT tested panels


Partner: DLR

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

]

Simulation - No considaration of degradation

Simulation with degradation of the adhesive (Reduction of E to 0.1%)

Test on Design 1

0

20

40

60

80

100

120

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0

Shortening [mm]

Load

[kN

]

No degradation UMAT implicit standardUMAT implicit advancedFirst von Mises failureFigure 1Figure 2Figure 3Figure 4

Simulation of DLR Design 1 panelReduction of E->0.1%

Max Strength of the adhesive layer 48 MPa

DLR Design 1 panel -USDFLD

DLR Design 1 panel – UMAT implicit


Simulation of buckling and post buckling with adhesive and ply

degradation.

0

50

100

150

200

250

0 20 40 60 80 100Opening (mm)

Load

(N)

Eperiment 1 Eperiment 2



Smax = 3.6 Gc = 0.96 Smax = 3.1 Gc = 1.1

0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5Shortening [mm]

TEST P29Elastic Ply - Elastic Interface

Elastic Ply - Damage InterfacePly Degradation - Elastic Interface

Ply Degradation - Damage Interface

Simulation of Skin-Stringer separation

Partner: SAMTECH


0

5

10

15

20

0.00 0.50 1.00 1.50 2.00

Rotation [deg]

Torq

ue [k

Nm]

FE - Damaged box

SN4

100 200 300 400 500 600 700 800

Horizontal axis [mm]

500

600

700

800

900

1000

1100Ve

rtica

l axi

s [m

m]

-10.00-9.00-8.00-7.00-6.00-5.00-4.00-3.00-2.00-1.000.001.002.003.004.005.006.007.008.009.0010.00

Partner: POLIMITests and analyses of pre-damaged panels

Damagedareas

Zone A

Zone B

Zone C

Zone A Zone B Zone C

Tsai-Wu failure


1st Buckling & Collapse Load vs Damage Length

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00

Characteristic Damage Length [mm]

Nor

mal

ized

Loa

d

collapse: test

collapse: analysis

buckling:test

buckling: analysis

absent stringer

absent stringer

Conventional design is not too sensitive to damage size.

Even with detached or completely absent central stringer, the buckling and collapse loads do not change dramatically.

WP 6 – Design guidelines


Rib A

Rib B

Different (from COCOMAT) manufacturing process:

cobonded stiffeners instead ofcocured ones.

Different (from COCOMAT) material :

250°F per IAI MS instead ofCOCOMAT 350°F IM7/8552

WP 6 – IAI contribution - structure for industrial validation

Composite Stiffened Panel for A/C Stabilizer.Carbon/Epoxy Stiffened skin structure.Industrial validation, both analytical and experimental, for the section bounded by Ribs A & B. Test specimen has been manufactured by IAI and tested by TECHNION.


Summary

2004 20082004 2008


ProgrammTime Time Time

9.00

10.45 8.30 - 10.00 8.30 - 10.00

11.00 - 12.30 10.30 - 12.10 10.30 - 12.10

13.30 - 15.1012.10 - 15.00

13.10 - 14.50

15.40 - 17.40 15.00 - 17.00 15.20 - 17.00

18.00 17.15

18.30-22.30 18.00 - 20.0017.00

20.00

Registration

Transfer University - Dinner

3rd September (Day 1) 4th September (Day 2)

DLR - Technical visiting tour (Finger food available)

2) Dinner speech: Prof. Joachim Block (ROSETTA Lander - a challenging mission to the origins of the solar system)

Conference Dinner (Dornse)

1) Welcome by Mr. Lehmann (Chief city councilor of the City of Braunschweig)

Transfer DLR - Hotels

Semi-analytical concepts

Unstiffened structures II / Analysis and validation II

Analysis and validation I

Unstiffened structures I

End of Conference

Optimisation

Transfer University - DLR

5th September (Day 3)

Keynote lectures

COCOMAT - Workpackage summaries

Degradation I

COCOMAT - Achievements of the PhD students (Fast simulation tools, tests)

Structure tests

Keynote lecturesKeynote lecturesR. Degenhardt Welcome

Degradation II

Keynote lectures: Design handbooks

COCOMAT Workshop

Conference Venue:Technical University of Braunschweig,Pockelsstrasse 4 (Altgebäude), Braunschweig, Germany


Internet: www.cocomat.de

2nd int. conference on buckling and postbuckling behaviour ......buckling and postbuckling behaviour...

Documents