1. Finite Element Simulation of a Vertical Drop Test of a Boeing 737 Fuselage Section
A. Byar, J. Awerbuch, A. Lau and T. Tan
Drexel University
Department of Mechanical Engineering and Mechanics
Philadelphia, Pennsylvania
Presented at
Third Triennial International Fire & Cabin Safety Research Conference, October 22-25, 2001, Atlantic City, NJ

2. Acknowledgement
This work is sponsored by the FAA William J. Hughes Technical Center under Grant No.99-P-0056, and is part of the FAA-Drexel Fellowship Research Program.
Gary Frings and Tong Vu are the program monitors.

3. Outline of the Presentation
Objectives
Drop Test of B737 Fuselage Section
Finite Element Model and Simulation
Results
Deformation Time Histories of Frames
Acceleration Time Histories of Frames, Seat Tracks, and Overhead Bins.
Load Time Histories of the Supporting Structures of the Overhead Stowage Bins
Conclusions and Summary

4. Objectives
Develop a finite element model and conduct a dynamic simulation of the drop test of a Boeing 737 fuselage section.
Refine the finite element model through a comparison of the simulation and experimental results.
Develop a finite element based methodology to provide guidance for future testing conditions or configurations, and to simulate drop tests of other airframes that may be of interest in the future.

5. Drop Test of the B737 Fuselage Section
With Two Overhead Bins
Performed in November 2000 at the FAA William J. Hughes Technical Center
Ten foot long B737 fuselage section
Seven frames, from FS 380 to FS 500
A cargo door on the right-hand side
Two different overhead stowage bins
18 seats with dummy passengers
Luggage stowed in the overhead bins and the luggage compartment
Fully instrumented with strain gages and accelerometers
30 ft/sec initial impact velocity

6. Drop Test of the B737 Fuselage Section
Front View
Back View
Hitco Bin
Heath Tecna Bin

7. Drop Test of the B737 Fuselage Section

8. Finite Element Model Camera Mounts Hitco Bin Heath Tecna Bin Forward
Right
Left
Forward
Extra Under-
Floor Beams
Under-Floor Beams
Cargo
Door

9. Finite Element Model Camera Mount Heath Tecna Bin Forward Seat Tracks
Right
Left
Floor
Aft
Cargo Door

10. Finite Element Model Camera Mounts Hitco Bin Heath Tecna Bin Forward
FS 500
FS 480
FS 460
FS 380
FS 400
FS 420
FS 440
FS 500
FS 480
FS 460
FS 380
FS 400
FS 420
FS 440
Frame
Reinforcement
Reinforcement
Short Beams
Cargo Doorframe

11. Finite Element Model Hitco Bin Cylindrical Rod Vertical Tie Rod
FS 480
FS 460
FS 420
FS 400
Vertical
Link
Horizontal
Short Beam
Bin is modeled with shell elements
All supporting members are modeled with beam elements

12. Finite Element Model Heath Tecna Bin C Channel Strut Longitudinal
FS 480
FS 460
FS 420
FS 400
Longitudinal
Channel
L Bracket
Bin and C Channels are modeled with shell elements
All other supporting members are modeled with beam elements

13. Finite Element Model
57,589 Nodes, 56,652 Shell Elements, 67 Beam Elements.
Masses of cameras are distributed on the mounts
Masses of seats and passengers are lumped to the seat tracks.
Masses of
luggage in
overhead bins are
distributed in the bins
Masses of luggage in the luggage
compartment are distributed onto the lower frames.

14. Finite Element Analysis
LS-DYNA Explicit Code Used
Reduced-Integration Scheme Used for Shell Elements
Time Steps: Initial t = 410-6 sec., Final t = 110-6
30 ft/sec Initial Velocity, sec. response calculated
Fuselage Skin: 2024-T3 Aluminum
All Other Structural Members: 7075-T6 Aluminum
Bi-Linear Stress-Strain Laws Used
Material
Initial Stiffness
(106 psi)
Final Stiffness
Yield Stress
(103 psi)
2024-T3
10.3
0.61
28.0
7075-T6
0.65
72.0

15. Impact Energy Conversion
Elastic
Response
95% of impact energy converted to internal energy
Alan: Why is there a ~ 2 ms zero energy conversion at the very beginning?

16. Energy Absorption
60% of total
internal energy absorbed by frames

17. Results Deformation Time History of Frames
With Contour of Effective Plastic Strain

18. Plastic deformation at the bottom of the frames
Deformation Time History of Frames with Contour of Effective Plastic Strain
Plastic deformation at the bottom of the frames
Flanges of the bottom frames show plastic deformation

19. Deformation Time History of Frames with Contour of Effective Plastic Strain
Buckling of flanges at the lower left & right corners
Plastic deformation at lower left & right corners

20. Aft doorframe has very little deformation
Deformation Time History of Frames with Contour of Effective Plastic Strain
Aft doorframe has very little deformation
Flanges buckled

21. Plastic deformation in frames near the bin outboard supports
Deformation Time History of Frames with Contour of Effective Plastic Strain
Plastic deformation in frames near the bin outboard supports
Plastic deformation
Kinks formed in the LHS frames
Plastic hinges formed
Fuselage section tilts to the left
Energy mostly absorbed by the plastic hinges
Little deformation occurs in the upper portion

22. Deformation Time History of Frames with Contour of Effective Plastic Strain
Plastic deformation caused by camera mounts
Upper doorframe between FS 460 and FS 480 subject to high shear force
Beam/Frame Joints
Stiff aft doorframe causes RHS to deform more gradually
Plastic hinges hit the ground, set off a 2nd impact, primarily affecting LHS

23. Deformation Time History of Frames with Contour of Effective Plastic Strain

24. Deformation Time History of Frames with Contour of Effective Plastic Strain
Plastic deformation mostly occurs in lower frame
Lower left corner crushed
Lower right corner deforms much less
No plastic deformation in frame reinforcement above the doorframe
High shear force exerted by aft doorframe on upper doorframe
Load transmit to upper frame differently through front and aft doorframes
Little deformation occurs in aft doorframe

25. Deformation Time History
Simulation at 100 ms
Actual Drop Test

26. Acceleration Time History - Frames
Results
Acceleration Time History - Frames

27. Acceleration Time History - Frames
Aavg=58.0
Aavg=43.5

28. Acceleration Time History - Frames
LHS first peak value slightly higher
Plastic hinges delay the 2nd peak of LHS
Damping
2nd impact set off by LHS plastic hinges hitting the ground results in high acceleration on LHS
Elastic response after 100 ms

29. Acceleration Time History – Seat Tracks

30. Acceleration Time History – Seat Tracks
Aavg=13.6
Aavg=16.0
Aavg=16.6
Aavg=20.2

31. Acceleration Time History - Bins
Where?
Hitco Bin
Heath Tecna Bin
Accelerations calculated at the forward end,
the aft end, and the c.g. of each bin.

32. Acceleration Time History - Bins
Hitco Bin
Heath Tecna Bin
First peak accelerations
Range: 14.5 G to 15.5 G
Average = 15.0 G
Range: 9.7 G to 20.0 G

33. Load Time History - Bins
Secondary (outboard) supporting members.
Vertical and Horizontal Links
L Brackets
Primary vertical supporting structure
Tie Rods
Struts
Hitco Bin
Heath Tecna Bin

34. Load Time History – Bins Primary Supporting Structures
Hitco Bin
Heath Tecna Bin

35. Primary vs. Secondary Supporting Structures
Load Distribution
Primary vs. Secondary Supporting Structures

36. Load Distribution – Hitco Bin

37. Load Distribution – Heath Tecna Bin

38. Effect of Camera Mounts

39. Conclusions
Finite element prediction of the deformed fuselage configuration compared very well with that of the drop test.
95% of the impact energy converted to internal energy at approximately 90 ms.
60% of the internal energy is absorbed by the frames.
The stiff cargo doorframe on the right-hand side causes the fuselage to deform in an unsymmetrical manner and has a significant effect on both the overall response of the fuselage section and components such as overhead bins.
Under the current test condition the primary supporting members of Hitco bin (tie rods) carry approximately 55% of the total vertical load. Those of Heath Tecna bin (struts) carry approximately 75% of the total vertical load.
Cameras and camera mounts cause substantial plastic deformation in the frames, and have some effects on the responses of overhead bins.

40. Summary and Future Work
A finite element model has been developed to simulate the drop test of a B737 fuselage section. Preliminary results, in terms of the deformed configurations, compared very well with those of the drop test.
The finite element model will be further refined as the experimental data become available for comparison - work is underway.
Frames mesh needs to be refined
Luggage needs to be modeled more realistically for energy absorption.
Other issues include employing more accurate material laws, better damping models, failure criteria, etc.
Overhead bin certification can be greatly enhanced through a series of parametric studies using the finite element model.
Knowledge gained in this work can be used to develop a finite element based methodology to provide guidance for future testing conditions or configurations, and to simulate drop tests of other airframes that may be of interest in the future.