Structural Integrity of Hybrid Metal Composite Structures in a Fighter Aircraft

Presented at Flygteknik 2010 – Stockholm, October 18-19, 2010

NFFP – Structural Assessment of Hybrid Structures

Research programme aiming to develop the required methodology and data to certify complex metal/composite hybrid assemblages subjected to in-flight coupled thermo-mechanical load spectra.

Focused on test verification techniques to cover the significant effects of:

Thermal induced stresses - dissimilar thermal expansion - heat transfer into structure - speed & altitude - surrounding temperature

Load sequences - rare high peak loads - frequent small load ranges

Wing – Fuselage Attachment

A/B/C/D - versions

E/F - versions

Full-scale fatigue test of complete airframeand sub assemblages

xyFlight

yFlight y

Temp

P low LT

yFlight

xTemp

xyFlight

P high LT

Coupled thermo-mechanicalload cases

Typical temperatures (MIL-STD-1530C)

Gripen E/F – temperatures for static loads

Sustained – through all structure: -40oC +94oC

85oC 100oC

Example – Super Sonic Fighter Sweep

2

0 211 MTT

yFlight

xTemp

xyFlight

P LT

Flight and temperature loads

Heattransfer

StagnationTemperature To

Detailed FE-analysis of complete wing

156

2032

20

228

1632

64

156

D= 8

10Aluminium

9,4 9,4

2 x composite

2032

16

36

160

70

3650 22

8

232

D = 8

Fatigue testing of specimens exposed to heating

Dissimilar failure mechanisms – metal / compositeLoad sequence effects – retardation / accelerations

1E-7

1E-6

1E-5

1E-4

0.001

0.01

0.1

0.01 0.1 1 10 100

Energy Release Rate Range GI (N/mm)

Cra

ck/D

elam

inat

ion

Gro

wth

Rat

e (m

m/c

ycle

)

CFRP IM7/8552Layup 24/24-0-0Interface 0/0

Al-Alloy 7475-T761

R = 0.05

Sheet, t = 2 mmOrientation L-T

Metal predominating singel crack

Composites matrix cracking delamination fiber breakage interfacial debonding

Truncation or extension of high loads

composites (to verify life also for aircraft exposed to rare high loads)

composites

metals

metals (to verify life also for aircraft not exposed to rare high loads)

Elimination of insignificantload cycles

Fatigue test verification of metal and composite structure

Mean maneuver load spectra forone service life e.g. 8,000 hrs.

Load

rang

es

Log number of cycles

Zlatan KapidzikLars DjärvMartin EkströmHans EllströmJonas WahlbäckHans Ansell

Joakim SchönRolf JarlåsAnders BlomBörje Andersson

Participants – NFFP project