Foam Reinforced Aircraft Fuselage Study

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Foam Reinforced Aircraft Fuselage Study
Narasimha Harindra Vedala, Tarek Lazghab, Amit
Datye, K.H. Wu Mechanical And Materials
Engineering Department Florida International
University Miami, Florida
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Overview

• Propose a strategy to reduce the effect of
  fatigue failure
• Simulate the failure behavior of fuselages due
  fatigue using finite element analysis
• Determine the effect of reinforcement on fatigue
  life due to the new proposed strategy

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Fatigue Failure
It is defined as the failure of a metal
structure due to cyclic loading. Fatigue
Failure occurs at load amplitudes much lower than
the breaking load of the material
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• Fatigue Failure in Aircrafts
• Aging aircrafts fatigue analysis
• Pressurization and Depressurisation of the
  fuselage results in cyclic stresses

Aloha incident in 1988 caused due to fatigue
failure
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• How to reduce the effect of fatigue failure?
• Using composite materials for manufacturing
  fuselages.
• Using Reinforcement to the fuselage
• Pantherskin
• Research on polyisocyanurate foam at FIU since
  1988. Nicknamed as Pantherskin

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Why Pantherskin?

• Inexpensive foam
• Light weight Density 2 to 4 lb/ft3
• High fire resistance

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Fracture in metals

• Modes of Cracking in flat bodies
• (based on Linear Elastic Fracture Mechanics)
• Mode I
• Mode II
• Mode III

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Objective

• Study the effect of adding foam layer to stress
  distribution in the fuselage
• Generate a Finite Element model to conduct
  fatigue analysis on fuselage with foam
  reinforcement
• Compare with results from previous methods

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Fracture parameters

• Stress Intensity Factors
• It is defined a quantity that characterizes the
  severity of the crack situation
• For flat plate with infinite width
• Strain Energy Release Rate
• E Elastic modulus

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Verification study

• Procedure Verification
• Flat plate with central crack
• Results were compared with
• Rybickis (1977) model

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Finite Element Analysis

• Model Definition
• Aircraft fuselage can be considered as a cylinder
  with equal spaced cracks
• Considering
• symmetric
• geometry
• a section of the
• fuselage is used for
• finite element analysis

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Verification study Unstiffened curved panel

• Procedure
• Verification
• Compared
• with Youngs model
• using STAGS FE
• package
• Longitudinal crack configuration

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Bulging of crack in the fuselage
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FEA of Aircraft Fuselage

• Boeing B737
• obtained
• Configuration
• R74.018?
• t 0.036?
• Aluminum
• EA10.5 Msi vA 0.33
• Foam
• EF 3000 psi vF 0.3

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Components of fuselage
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Finite Element Model
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Boundary Conditions and loading
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Von Mises Stress
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Stress distribution in the panel when 2? foam is
added
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Fatigue Analysis

• Coffin-Manson equation

Cycles until failure.
Strain range

Slope of elastic strain amplitude vs. fatigue
life.
One reversal intercept of plastic strain vs. life
line.
On reversal intercept of elastic strain vs. life
line.
Slope of plastic strain amplitude vs. fatigue
life
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Fatigue Analysis
Fuselage panel with Longitudinal Crack 4.5?
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Global model and Submodel

• A submodel is generated to study the stress
  distribution near the crack
• Results for the global model are used for the
  nodes at the boundary of the submodel

Location of submodel in the global fuselage panel
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Von mises stress Distribution in Submodel
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Conclusion

• Reinforcement of the fuselage skin with foam help
  to reduce the stresses distribution
• 18 for 2 " foam layer
• 25 for 4 " foam layer
• A maximum of 32 reduction in stress intensity
  factor is possible for 4" foam addition
• A 3.7 fold increase in life of the aircraft is
  achievable if 4" foam is used
• A parametric is developed which can be used for
  different fuselage configurations

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References

• Chen, D.,(1991), Bulging of Fatigue Cracks in a
  Pressurized Aircraft Fuselage, Ph. D.
  Dissertation, Department of Aerospace
  Engineering. Delft, The Netherlands Delft
  University of Technology
• Rybicki, E.F., Kannien, M.F.,(1977) A Finite
  Element calculation of stress intensity factors
  by a modified crack closure integral.
  Engineering Fracture Mechanics, Vol. 9, pp.
  931-938
• Ahmed, A.A, Backukas, J., Jr. and Paul W. Tan,
  Awerbuch J., (2002) Initiation and distribution
  of multiple-site damage (MSD) in fuselage lap
  joint curved panel, Sixth Joint FAA/DoD/NASA
  Conference of Aging Aircrafts, Albuquerque, San
  Francisco, CA.
• Torres, M.J. and Wu, K.H., (1993), A New
  Approach to solve aging airplane problems using
  Polyisocyanurate, Journal of Cellular Plastics,
  Vol. 29, N4, p.p 380.
• Rahman, A., Backukas J.G., Jr., Paul W. Tan, and
  Catherine A. Bigelow,(2002), Bulging Effects on
  longitudinal cracks in lap joints of pressurized
  aircraft fuselage, Sixth Joint FAA/DoD/NASA
  Conference of Aging Aircrafts, Albuquerque, San
  Francisco, CA.

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Future Research

• Several modeling issues were encountered
• Numerical formulation for defining fracture
  parameters for composite materials is not yet
  available
• Results have to be verified by experimental tests

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Questions