Jegley, Dawn

Velicki, Alexander

NASA Technical Reports Server

National Aeronautics and Space Administration 
www.nasa.gov 
Status of Advanced Stitched Composite Aircraft Structures  
AIAA Aero Sciences Meeting 
January 4-7, 2011 
Dawn Jegley          Alexander Velicki 
NASA Structures Lead          Boeing PI 
Environmentally Responsible Aviation 
Integrated Systems Research Program 
https://ntrs.nasa.gov/search.jsp?R=20110011740 2019-08-30T15:48:23+00:00Z
Challenges of Hybrid Wing Body Center Section"
•  Pressurized non-circular center section"
–  Compound curvature"
–  Almost 90-degree angles at joints"
–  Fatigue"
•  Bi-directional in-plane loading "
–  Continuous load paths in both direction"
–  Integral design without shear clips"
•  Manufacturable"
–  Large integral components"
–  Out-of-autoclave process"
•  Economical"
–  Hard metal tooling on OML only"
–  Simplified bagging process for IML"
–  Fabricate entire cover panel in one cure"
•  Damage Tolerant"
–  Arrest damage resulting from discrete source damage "
–  Minimal delamination"
•  Acceptable acoustic response"
2 
Spanwise 
Loading 
Nx 
Internal 
Pressure 
Streamwise 
Loading 
Nz 
Ny 
Pultruded Rod Stitched Efficient Unitized Structure"
3 
Stitched Structure Development"
LAIRCM Fairing"
Gear Doors"
Integral Fuselage"
Lightly-Loaded 
Secondary Structure!
Moderately-Loaded 
Structures!
Highly-Loaded 
Structures!
Unitized!
Structure! Complex 
Integration!
C-17 Prototype !
Nose 2005!
Large Panel Air Force 2006!
Fairing!
First Flight 2003!
NASA/Boeing!
ACT Technology!
1990-2000!
Hybrid 
Wing 
Body!
C-17 Production!
Main 2006!
Curved 
Panel 2008!
4 
Initial Objective:  Develop concept for HWB center"
5"
Subcomponents"
Verify improvements with!
vehicle-level analysis and 
refine analysis codes!
Element-level Specimens"
Combined Load:!
!- Spanwise Axial!
!- Chordwise Axial!
!- Internal Pressure!
Trades Studies"
•   Stringer and Frame Directions!
•   Static Axially Loaded (Fx and Fy)!
•   Pressure Box (Fn)!
•   Analytical Predictions!
•   Stringer and Frame Directions!
•   Static Axially Loaded!
•    Analytical Predictions!
•   Test Loads!
•  Panel 
Geometry!
TRL 4 -  Validation by Test!TRL 3 - Proof of Concept!
Buckling of large 
unsupported 
spans!
Damage arrestment 
for minimum gauge 
panels!
Bending and out-of-plane 
loading for minimum gauge 
panels!
HWB Vehicle Sizing"
6 
Aeroelasticity 
NASTRAN 
Solution 200 
Constant Set of Running Loads 
Panel Optimization 
Global Analysis 
Local Analysis 
Stiffness 
Mass Distribution 
Linear Aero 
(NASTRAN Sol 144) 
Local Panel Sizing Req'mts 
  • Strength and Stability 
  • Local Geometry Effects 
  • Material and Mfg Constraints 
Fuselage 
Design Region 
Panel Geometry 
Vehicle Level 
Requirements 
Material Properties 
Property 
Update 
Panel Level Requirements 
Fuselage 
Concept 
Updated Design Allowables in 
Phase II based on Phase I Testing 
Embedded Sizing Equations 
Bottoms-up Wts 
Vehicle FEM 
Updated HyperSizer Code 
Tailored for PRSEUS in
Phase II 
Flat PRSEUS Panel Fabrication"
•  Insert text here"
7 
Tear Straps Placed Skins Placed Automated Preform Stitching 
Preform on Mold Tool Resin Infusion Cured Panel 
Manufacturing, Coupons, Design and Mechanics"
•  Material characterization"
•  Thermal effects on properties"
•  Fatigue studies"
•  Rod-wrap interface improvements"
•  Positioning aids to improve dimensional tolerance"
•  Ideal stitching pattern"
•  Improved bagging methodology"
•  Simplified analysis methodologies"
8 
Compression Panel"
9 
Measured Full Field Axial Strain IML Specimen Surface 
Possible 
Edge 
Effects 
Max Strains 
Panel 
CL 
Axial Strain 
Frame 
CL 
Frame 
CL 
C C
 Failure 
Region 
Predicted  
Critical 
Locations 
Damaged Tension Panel Test"
•  Insert text here"
10 
Stringer 
Failure "
Stringer 
Failure"
Skin 
Failed"
Paint 
Mismatch 
Stringer 
Shifted"
Broken 
Stitching"
Frame 
Flange 
Separation"
Free 
Edge 
Effects"
Rod Pulled 
Out"
Rod Pulled 
Out"Wrap Failed"
Wrap 
Failed"
Free 
Edge 
Effects"
Flat PRSEUS Pressure Panel"
•  Minimum gage skin (.052 in.)"
•  Met 2P (18.4 psi) requirement with no damage"
•  20 ft-lb internal damage to rod-stiffener"
•  Sustained 3P with damage"
•  Failure in rod-stiffener but continued to hold pressure to 30 psi"
11 
!"#$%&'()#*'(
+,,&-./(0(#1/(
23)45)(3-6(
)*&#17'&(
8'9(
)*&#17'&(
!$"17'(
0.5 in."
w"
0.1 in."
18 psi"
PRSEUS Progress"
12 
NRA Phase I Specimens 
Trades 
Studies 
•  Panel 
Geometry 
28 psi with no damage 
PRSEUS 
10.4% 
lighter.  
improved buckling 
stability.  
Combined 
axial & pressure 
loading test at NASA 
COLTS Facility 
•  Weight 
Goals •  Test 
 Loads 
10% better than sandwich. 
test stability 
failure 
75% higher than 
strength design 
allowable. 
withstand 2P 
(18.4 psi) load case.  
arrested 
damage at 1.5 
times 
initiation load.  
within 5% of static 
results after 2 
fatigue lives.  fatigue failures 
within 5% of static 
test results. 
Arrested damage at 3 
times higher than 
initiation load level. 
general panel buckling 
at -5,000 lbs/in.  
Compression 
panel test 73 
kips/frame. 
Pressure Cube Multi-bay Box 
NRA Phase I Trades 
Stringer 
Frame  
Curved Pressure Panel"
•  IM7-VRM-34"
•  127 inches long"
•  75 inches wide (with doublers)"
•  90-inch radius"
•  24-inch frame spacing"
•  7.8-inch rod-stiffener spacing"
13 
Panel delivered to NASA Dec. 2010 "
Testing scheduled for summer 2011"
Curved Pressure Panel Test"
•  Pristine panel"
–  apply 18.4 psi"
–  apply 9.2 psi and DLL tension"
•  Panel with barely visible damage"
–  apply 9.2 psi and DLL tension"
–  apply 13.8 psi and DUL tension"
•  Panel with Discrete Source Damage"
–  apply 9.2 psi with DLL"
–  apply axial load to failure with no pressure"
•  Tests planned for summer 2011"
14 
FAA FASTER Facility"
(Full scale Aircraft Structure Test 
Evaluation and Research facility)"
Repair Concepts"
15 
•  Design, Testing and Analysis"
–  Requirements: (1) Restore load carrying capability of a pristine structure  
(2) Minimize need for specialized equipment/methods"
–  Bolted metallic repair; "
–  DSD tension panel used as a baseline"
Stress Finite 
Element 
Analysis 
Repair Assembly 
Tension-Loaded 
Crack-Arrestment 
Test Panel 
Baseline 
Interior repair"
plates"
External "
strap"
Acoustics"
16 
•  Experimentally characterize PRSEUS panel without acoustic treatment"
•  Validate finite element (low freq.) and statistical energy (high freq.) analyses"
•  Propose effective acoustic treatment with minimal weight penalty"
Structural Acoustics Loads 
and Transmission facility 
(SALT) 
Finite Element 
Model 
Fundamental 
Mode 
LaRC SALT facility 
Panel test in 
2011 
Damage"
•  Damage arrestment at stitch lines"
–  experimental evidence"
–  corresponding analytical predictions"
•  Structural Health Monitoring"
–  damage around stitches"
–  Rod-overwrap region"
•  Fatigue and damage growth"
•  Stitching/damage suppression and arrestment opens the door to more efficient 
design"
17 
Multi-bay Test Article Development Approach"
18 
Test 
Region 
BWB 
Baseline 
Combined Loads 
Test Facility 
(NASA-LaRC) 
Pressure 
and Axial 
Loading 
Pressure 
Cube  
(~48" wide) 
Large-Scale Test 
Article 
(80% scale) 
Pressure Cube - Risk Reduction"
Large-scale 
Test Article  
Cube 
Floor 
Pressure Cube Design  
(52" x  48” x  56” Tall) 
Crown 
Panel 
Rib 
Panel 
Integral 
Caps 
Bkhd Panel 
Removed for 
Clarity 
•  PRSEUS panels on all sides"
•  Evaluate joint behavior"
•  Load in pressure only to 2P 
(18.4 psi)"
•  Impact at critical joint location"
•  Supports multi-bay box design"
19 
Pressure Cube Benefits"
•  A build up of highly integrated structural panel 
assemblies"
•  Integrated structures eliminates fit-up issues 
during assembly"
•  Stitching increased pull-off capability and 
enables a fail-safe design approach"
•  PRSEUS concept reduces panel fabrication 
tooling costs"
•  No final assembly tooling required"
•  Drastic part reduction"
•  Reduced assembly time"
20 
Multi-bay Box Overview"
Center Keel 
Panel 
(PRSEUS) 
Floor Panel 
(PRSEUS) 
Center Ribs 
(Honeycomb) 
Crown 
Panel 
(PRSEUS) 
Fwd & Aft 
Bulkhead Panels 
(PRSEUS) 
Outer Rib 
Panels 
(PRSEUS) 
Intercostals 
(Aluminum) 
Note: Fwd Bulkhead 
Panels Removed for 
Clarity 
Adapter 
Boxes 
(Aluminum) 
Side Keel 
Panels 
(PRSEUS) 
•  Multibay Box overall dimensions "
–  ~30ft x 7.3ft x 18.3ft"
•  Approximate Volume = 2350 ft3"
21 
Multi-bay Test in NASA LaRC COLTS Facility"
22 
•  Test conditions"
–  Pressure loading to 2P (18.4 psi)"
–  Axial Bending to 2.5G"
–  Combined Axial loading and 1P (9.2 psi)"
•  Analysis including loads as applied by 
COLTS"
•  Delivered and tested in 2010"
Future Plans"
•  Pressure cube test:  April 2011"
•  Multi-bay box test:  2012"
•  Circular fuselage development  2011-2015"
•  Damage tolerance studies  2011-2015"
•  PRSEUS wing development"
•  Flight vehicle  "
24 
Summary of PRSEUS development"
25 
•  PRSEUS development supported by NASA, Boeing, FAA and AFRL"
•  Stitching is used to suppress interlaminar failures, arrest damage and turn 
cracks"
•  Damage arrest design principles already demonstrated in flat panels"
•  PRSEUS allows for non-circular pressurized center section to withstand 
repeated pressure and flight loads"
•  Unitized structure simplifies final assembly"
•  Out-of-autoclave processing allows for cheaper fabrication and quicker 
and easier changes to designs"
•  Validation of predictions for built-up structure still needed"
•  Combined axial and pressure loading will be achieved by a near-full-scale 
30-foot multi-bay box representing the center section of a HWB vehicle"


Status of Advanced Stitched Composite Aircraft Structures

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