Analysis of Fastener Disbond Arrest Mechanism for...
Transcript of Analysis of Fastener Disbond Arrest Mechanism for...
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The Joint Advanced Materials and Structures Center of Excellence
Analysis of Fastener Disbond Arrest Mechanism for Laminated Composite Structures
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The Joint Advanced Materials and Structures Center of Excellence 2
FAA Sponsored Project Information
• Principal Investigator:
• Dr. Kuen Y. Lin, Aeronautics and Astronautics, UW
• Research Scientist: Dr. Andrey Styuart, UW
• PhD Student: Chi Ho “Eric” Cheung, UW
• Undergraduate Research Assistant: Phillip Gray, UW
• FAA Technical Monitors: Lynn Pham, Curtis Davies
• Other FAA Personnel: Larry Ilcewicz, Peter Shyprykevich (Ret.)
• Industry Participants: Gerald Mabson, Eric Cregger, Marc Piehl, Cliff Chen, Lyle Deobald, Alan Miller, Steve Precup (All from Boeing)
• Industry Sponsors: Boeing
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Accomplishments
Work Accomplished: Phase 1 (“Development of Reliability-Based Damage Tolerant Structural Design Methodology”)
Developed the methodology to determine the reliability and maintenance planning of damage tolerant structures.
Developed a user-friendly software (RELACS) for calculating POF and inspection intervals.
Developed software interface (VSTM) with Nastran to facilitate stochastic FEA. Implemented stochastic FEA to obtain initial/damaged residual strength
variance.
Current Research Develop analytical methods to analyze disbond and delamination arrest
mechanisms in bonded structures under mixed mode loading. To apply probabilistic methods to assess reliability of bonded structures with
fasteners.
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Analysis of Disbond/Delamination Arrest Mechanisms
Objectives - To understand the effectiveness of delamination/disbond arrest mechanisms - To develop analysis tools for design and optimization
Tasks 1). Establish FE models in ABAQUS
2). Develop 1-D (beam) and 2D (plate) analytical capabilities 3). Implement reliability analysis capability 4). Conduct sensitivity studies on fastener effectiveness and stacking sequence effects
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Bonded Skin/Stiffener with Fasteners
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Laminate Configuration (16 plies)
0-ply Lay-up Ex C (in/lb)
(joint compliance) 25.0% (45/0/-45/90/45/0/-45/90)s 7.42×106 7.73×10-6
37.5% (45/0/-45/0/45/0/-45/90)s 9.29×106 6.57×10-6
50.0% (45/02/-45/02/902)s 1.10×107 5.85×10-6
62.5% (45/03/-45/02/90)s 1.30×107 5.25×10-6
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The Joint Advanced Materials and Structures Center of Excellence
Results: Applied Moment Only
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The Joint Advanced Materials and Structures Center of Excellence
Mode Decomposition with Fastener: Applied Moment Only
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The Joint Advanced Materials and Structures Center of Excellence
Results: Applied Tension Only
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Mode Decomposition: Applied Tension Only
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Friction and Fastener Preload
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Mode II Test Specimen
• Classical “bending type” specimen not suitable, e.g. SLB, ENF – Relatively thick compared to specimen length; specimen
dimension coupling – Limited space for crack to propagate
• We want “axial type” specimen to test crack arrest behavior – Symmetric, 3-beam model, load applied to the center beam
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The Joint Advanced Materials and Structures Center of Excellence
Mode II Test Specimen Preliminary Findings
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Mode II Test Specimen in 3-D
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Analytical Approach
• Uses Rayleigh-Ritz method and the energy principle. • Two beams, fastener (two springs), and an elastic foundation layer
between beams. • Elastic layer is composed of N individual springs where k is very
large in compression and zero in tension, for contact and separation.
• Solve system for the state of minimum potential energy iteratively. • SERR mode decomposition by Wang/Qiao.
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Rayleigh-Ritz Method (PMPE)
Beam Energy Terms
Elastic Layer Energy
Fastener/Spring Energy
Work Terms
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Shape Functions
• Shape functions must satisfy geometric boundary conditions. – Shape functions considered for transverse displacement.
• Shape functions considered for axial displacement
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Mode I: FEM vs. Analytical Fracture Analysis
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Mode II: FEM vs. Analytical Fracture Analysis
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Analytical Model Enhancements
• Opposite axial forces causes a bending moment that counteracts the relative displacement of the beams at the location of the fastener.
• Traction acting on intact portion of the beams contributes to moment coupling through equilibrium requirements.
• Use piece-wise adaptive shape functions to model the entire beam
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Work in Progress / Future Work
• Develop analytical solutions • Consider all alternate failure modes • Model crack propagation around the fastener in 3-D • Consider multiple fasteners • Design validation experiments • Generate design curves • Identify key variables for design and optimization • Perform parametric/sensitivity analyses
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A Look Forward
Benefit to Aviation – Provide analysis tools for fastener arrest mechanism – Provide a fail-safe path to the design of integrated
composite structures – Optimization can lead to weight savings while
properly addressing safety issue – Integrating with probabilistic analysis method can
properly address design uncertainties
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[back up] Model Description
16-ply CFRP ( t = 0.0075” x 16 = 0.12” ) Lay-ups
Percentage of 0-deg: 25% / 37.5% / 50% / 62.5%
Fastener Ti-Al6-V4 (E = 16.5x106psi) d = 0.25 in
Fastener Flexibility (H. Huth, 1986)
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[back up] Material Properties (AS4/3501-6)
• E1=127.5GPa • E2=11.3GPa • G12=6.0GPa • ν=0.3 • Xt=2282MPa • Xc=1440MPa • Yt=57MPa • Yc=228MPa • Sxy=71MPa • GIC=0.2627N/mm • GIIC=1.226N/mm • η=1.75
• E1=18.5Msi • E2=1.64Msi • G12=0.871Msi • ν=0.3 • Xt=331ksi • Xc=208.9ksi • Yt=8.3ksi • Yc=33.1ksi • Sxy=10.3ksi • GIC=1.5lb/in • GIIC=7.0lb/in • η=1.75