Effective Modeling of Thin-Film Shells Exhibiting Wrinkling Deformations · PDF fileEffective...
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Effective Modeling of Thin-Film Shells Exhibiting Wrinkling Deformations
David W. Sleight, Alex Tessler, and John T. WangAnalytical and Computational Methods Branch
NASA Langley Research Center
FEMCI Workshop 2003May 7-8, 2003
Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Outline
MotivationObjectivesShell modeling strategiesNumerical and experimental resultsConclusions
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Wrinkling in Solar Sails
Wrinkling- Large displacements- Low strain energy- Rigid-body motion
Detrimental effects- Performance- Stability- Maneuverability- Local heating
Testing difficult- Large size- Gravity- Aerodynamics
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Objectives
Explore nonlinear shell modeling of thin-film membranes using ABAQUSAchieve high-fidelity wrinkling predictions Perform experimental validation
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Shell Modeling
Characteristics- Bending and membrane coupling
effects included- Geometrically nonlinear shell
deformations
Capabilities- Wrinkling amplitude, wave length
and shape- Membrane-to-bending coupling
using imperfections- Buckling modes (Wong &
Pellegrino, 2002)- Trigonometric functions (Lee &
Lee, 2002)Wong & Pellegrino
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Shell Analysis Issues
Wrinkling initiation issues- Shear locking for thin shell elements- Membrane-to-bending coupling in initially
flat membranes- Numerical ill-conditioning of tangent
stiffness matrix- Sensitivity to modeling, loading, and B.C.’s
Modeling and computational strategies- Employ robust shell elements - Introduce computationally efficient,
unbiased random imperfections (w0)- Add fictitious viscous forces to circumvent
numerical ill-conditioning- Remodel sharp corners and concentrated
loads
σ
w0
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Numerical and Experimental Results
Square thin-film membranes- Shear loaded
- Tension loaded
∆
P
P
P
P
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
ABAQUS Shell Modeling
Basic modeling strategies- Use robust, locking-free, shell
element- Add fictitious viscous forces
to circumvent numerical ill-conditioning (STABILIZE)
- Introduce small, unbiased, random transverse imperfections to enable membrane-to-bending coupling
S4R5
0FIPvM cF
v
v A
=−−=
hw random0 ⋅δ⋅α=
10.0=α[ ]1 , 1 random −∈δ≡δ
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Shear Loaded Thin-Film Membrane
∆ = 1 mm
a
a
229Edge length, a (mm)
0.38Poisson’s ratio, ν3790Elastic modulus, E (N/mm2)
0.0762Thickness, h (mm)
Mylar® Polyester Film Properties
Experiment: J. Leifer (2003)
Tested at NASA LaRCPhotogrammetry
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Experiment vs. Simulation
Experimental Observations using Photogrammetry
ABAQUS Nonlinear Shell FEA
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Experiment vs. Simulation
Random imperfections imposedActual initial imperfections not used
+1.18+0.82+0.46+0.09-0.27-0.63-0.99-1.35-1.71-2.07-2.43-2.79-3.15
+0.67+0.36+0.04-0.27-0.59-0.90-1.22-1.53-1.85-2.16-2.48-2.79-3.11
w (mm)w (mm)
ABAQUS Nonlinear Shell FEAExperimental Observations using Photogrammetry
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Tension Loaded Thin-Film Membrane
2.45 N
2.45 N
Kevlar threads
Kevlar threads
a
500Edge length, a (mm)
0.34Poisson’s ratio, ν
2590Young’s modulus, E (N/mm2)
0.0254Thickness, h (mm)
KAPTON® Type HN Film Properties
Experiment: J. Blandino & J. Johnston (2002)
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Simulation from Corner Point Loads
+0.61+0.48+0.35+0.22+0.09–0.04–0.17–0.30–0.43–0.56–0.69–0.82–0.86
w (mm)
Deflection
Von Mises Stress
Corner region 0.10w0.10- FEA ≤≤
Quad elements collapsed into trianglesSevere stressconcentration
+31.74+29.11+26.48+23.86+21.23+18.60+15.97+13.35+10.72+ 8.09+ 5.46+ 2.84+ 0.21
σ (N/mm2)
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Shell Modeling with Truncated Corners
Basic modeling strategiesAdditional enhancements- Remove sharp corners
where loads applied- Represent point loads
as distributed tractions
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Truncated Corners Model
+18.96+17.74+15.83+14.27+12.71+11.15+ 9.58+ 8.02+ 6.46+ 4.90+ 3.33+ 1.77+ 0.21
σ (N/mm2)
• Sharp corners removed• Stress concentration reduced• Good correlation with experimental
results
Von Mises Stress
Corner region
Sharp corners removedSevere concentration reducedWrinkles develop
+0.34+0.24+0.14+0.04–0.06–0.16–0.26–0.36–0.46–0.56–0.66–0.76–0.86
w (mm)Deflection
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Experiment vs. Simulation
ABAQUS Nonlinear Shell FEAExperimental Results(J. Blandino, 2002) W (mm) W (mm)
Random imperfections appliedSymmetric wrinkle pattern
Initial imperfections presentNon-symmetric wrinkle pattern
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Conclusions
Large displacement shell modeling of thin-film membranes to achieve wrinkling deformations- Robust shell elements free of shear locking- Fictitious viscous forces to circumvent numerical ill-conditioning - Unbiased random transverse imperfections to enable membrane-
to-bending coupling- Improved modeling of sharp corner regions subjected to tension
loads
Numerical examples and experimental validation- Square membranes loaded in shear and tension- Numerical results compared favorably with experiments
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Analytical and Computational Methods Br.Structures and Materials CompetencyNASA Langley Research Center
Conclusions (cont.)
Remaining Issues- Element technology- Nonlinear analysis convergence and viscous-force stabilization- Adaptive mesh refinement / robust error estimation- Sensitivity to boundary conditions and applied loading