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Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Buckling & Post-buckling Behavior of
Thin Composite Panels
CSIR-NALCSIR
Ashwin Rai, S Nadeem Masood, S R Viswamurthy,
Saurabh Chandrakar, Arun Kumar Singh,
Kodukula Swapna & Kotresh M Gaddikeri
Advanced Composites Division
National Aerospace Laboratories
Council of Scientific & Industrial Research
Bangalore, India
International Digital Image Correlation Conference & Workshop, September 15-18, Dublin
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
About NAL-CSIR
Established in 1959
CSIR-NAL mandate
Develop Aerospace Technologies with Strong ScienceContent
Support all National Aerospace Programmes
Design and Build Small and Medium–sized Civil Aircrafts
HANSA: 2 seat, all-composite, trainer aircraft
SARAS: Multi-role, light transport aircraft (14 seat)
CNM-5: Five seat general aviation aircraft
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
About Advanced Composites Division (ACD)
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Composites usage in Aircrafts
Source: Teal Group, Boeing, Airbus, Composite Market Reports
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Buckling as a Design Limitation
Current Design Scenario
First Buckling Load = 150% LL and above
Load
End Shortening
UltimateLoad (UL)
LimitLoad (LL)
Final collapse
Unused reserved strength of panel
First Buckling Load
End Shortening
UltimateLoad (UL)
LimitLoad (LL)
Final collapse
Improvement in structural efficiency
Future Design Scenario
Skin stiffener construction commonly found in aircraft structures
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Compression Testing of Large Composite Panels
Lanzi & Giavotto, 2006
Test Simulations
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Compression Testing of Large Composite Panels
Pevzner et al., 2008
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Composite Test Panel
800 m
m
130mm 130mm 130mm
Stringers
450 mm
Layup Sequence for skin: [+45/-45/0/90]s
(t=1.52 mm)
Layup Sequence for stringers : [+45/-45/0/0/
+45/-45/0/90]s (t=3.04 mm)
Stringer height, h = 20mm
Prepreg Material :
Hexply M21/34%/UD194/IMA-12K/300mm
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Post-Buckling Test Setup
Panel stringer side instrumented with
linear SGs & SG Rosettes
17 locations on skin
18 SGs on stringer web
One SG on stringer flange
Panel skin side is speckled for DIC
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Post-Buckling Test Setup
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Post-Buckling Test
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
DIC Set up
3D DIC measurements using Vic-Snap
AOI: 680 x 450mm (full exposed panel)
Camera: PointGrey 5MP Grasshopper 15 fps
firewire: 2 nos.
Lenses: Schneider 17mm
Image acquired every 2 sec
Calibration grid: 12x9 grid with 35mm spacing
Subset size: 55 by 55 Pixels
UTM loading rate: 0.12 mm/min
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Vertical Displacement ContoursComparison Test and Simulations
End Shortening= 0.35mm Load = 41.35kN
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Vertical Displacement ContoursComparison Test and Simulations
End Shortening= 0.65mm Load = 76.98kN
Near Horizontal Bands
Imply Uniform Loading
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Load vs End-shortening
0
20
40
60
80
100
120
140
160
0 0.5 1 1.5 2 2.5
Load
(kN
)
End Shortening (mm)
Numerical Simulation
Test 17
Simulations
Local Skin Buckling
Load = 93.20 kN
ES = 0.84 mm
Test
Local Skin Buckling
Load = 94.66kN
ES = 0.82 mm
FE Analysis Test – DIC Measurements
OUT OF PLANE DISPLACEMENT ‘W’
LOAD (FE) = 0 kN
LOAD (Test) = 0 kN
END SHORTENING = 0 mm
FE Analysis Test – DIC Measurements
OUT OF PLANE DISPLACEMENT ‘W’
LOAD (FE) = 22.22 kN
LOAD (Test) = 24.42 kN
END SHORTENING = 0.2 mm
FE Analysis Test – DIC Measurements
OUT OF PLANE DISPLACEMENT ‘W’
LOAD (FE) = 49.94 kN
LOAD (Test) = 53.10 kN
END SHORTENING = 0.45 mm
FE Analysis Test – DIC Measurements
OUT OF PLANE DISPLACEMENT ‘W’
LOAD (FE) = 77.61 kN
LOAD (Test) = 82.33 kN
END SHORTENING = 0.7 mm
FE Analysis Test – DIC Measurements
OUT OF PLANE DISPLACEMENT ‘W’
LOAD (FE) = 103.77 kN
LOAD (Test) = 107.25 kN
END SHORTENING = 0.95 mm
FE Analysis Test – DIC Measurements
OUT OF PLANE DISPLACEMENT ‘W’
LOAD (FE) = 124.68 kN
LOAD (Test) = 128.73 kN
END SHORTENING = 1.2 mm
FE Analysis Test – DIC Measurements
OUT OF PLANE DISPLACEMENT ‘W’
LOAD (FE) = 144.04 kN
LOAD (Test) = 139.71 kN
END SHORTENING = 1.45 mm
FE Analysis Test – DIC Measurements
OUT OF PLANE DISPLACEMENT ‘W’
LOAD (FE) = 154.33 kN
LOAD (Test) = 143.56 kN
END SHORTENING = 1.7 mm
FE Analysis Test – DIC Measurements
OUT OF PLANE DISPLACEMENT ‘W’
LOAD (FE) = 152.26 kN
LOAD (Test) = 144.37 kN
END SHORTENING = 1.95 mm
FE Analysis Test – DIC Measurements
OUT OF PLANE DISPLACEMENT ‘W’
LOAD (FE) = 152.60 kN
LOAD (Test) = 144.16 kN
END SHORTENING = 2.20 mm
Buckling Load (FE) = 93.20 kN
Buckling Load (Test) = 94.66 kN
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Strain Measurements
-5000
-4000
-3000
-2000
-1000
0
1000
2000
0 20 40 60 80 100 120 140
Mic
rost
rain
s
Load (kN)
S4 '0' Deg RSG
S4 '0' Deg DIC
-5000
-4000
-3000
-2000
-1000
0
1000
0 20 40 60 80 100 120 140
Mic
rost
rain
s
Load (kN)
S13 RSG
S13 DIC
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Summary
DIC is used to capture buckling and post-buckling behavior of
large composite panel subjected to compressive loads
DIC is ideal for capturing buckling modes & resulting out-of-
plane displacements
Provides very useful insight in the transition regime from local
skin buckling to global buckling of panel
DIC provides information on the uniformity of load distribution
Number of strain gages reduced drastically
Next, we plan to use DIC to study stiffener deformation deep in
the post-buckling regime
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
References
1. Lanzi & Giavotto, Composite Structures, Vol.73, 2006, pp.208-220.
2. Zimmermann, Klein & Kling, Composite Structures, Vol.73, 2006, pp.150-161.
3. Degenhardt, Kling, Klein, Hillger, Goetting, Zimmermann & Rohwer, InternationalJournal of Structural Stability & Dynamics, Vol.7, No.2, 2007, pp.337-358.
4. Pevzner, Abramovich & Weller, Composite Structures, Vol.83, 2008, pp.341-353.
5. Ghilai, Feldman & David, International Journal of Structural Stability & Dynamics,Vol.10, No.4, 2010, pp.917-926.
Aerospace Electronics and Systems Division
CSIR-National Aerospace Laboratories, IndiaInternational Digital Image Correlation Conference & Workshop, September 15-18, Dublin
CSIR-NALCSIR
Acknowledgments
M/s Pyrodynamics
M/s Correlated Solutions
Director, NAL
Head, Advanced Composites Division
Aeronautics Research & Development Board, India
