1 The Witness Sample Approach to Prognosis A. F. (Skip) Grandt School of Aeronautics and Astronautics Purdue University Currently USAF Academy Department of Engineering Mechanics AFOSR Workshop on Prognosis of Aircraft and Space Devices, Components, and Systems Cincinnati, OH, 19-20 February 2008
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1 The Witness Sample Approach to Prognosis A. F. (Skip) Grandt School of Aeronautics and Astronautics Purdue University Currently USAF Academy Department.
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The Witness Sample Approach to Prognosis
A. F. (Skip) GrandtSchool of Aeronautics and
AstronauticsPurdue University
Currently USAF Academy Department of Engineering Mechanics
AFOSR Workshop on Prognosis of Aircraft and Space Devices, Components, and Systems
Cincinnati, OH, 19-20 February 2008
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OutlineObjective: Review simple technique to evaluate
structural usage in context of potential for fatigue/corrosion damage
Describe “serial number” tracking concept
Topics:Overview witness sample approachReview prior work
Gage measures severity of structural loads (fatigue damage
potential)
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Summary: Research Needs
• Gage attachment • Develop/evaluate attachment for long
term performance• Side-groove consistency
• Control machining and/or stress relief• “Tweak” design parameters• Remote measurement of gage crack
length• Develop/evaluate inspection method
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Summary• Other potential prognosis applications
• Corrosion monitoring feasible• Potential for fatigue crack “nucleation”
and/or total life applications
• Key idea: actual damage (fatigue, corrosion, creep . . .) in redundant component can tell much about severity of parent structural usage
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References
J. P. Gallagher, A. F. Grandt, Jr., and R. L. Crane, “Tracking Crack Growth Damage in US Air Force Aircraft,” Journal of Aircraft, Vol. 15, No. 7, July 1978, pp. 435-442.
N. E. Ashbaugh and A. F. Grandt, Jr., “Evaluation of a Crack-Growth Gage for Monitoring Possible Structural Fatigue Crack Growth,” Service Fatigue Loads Monitoring, Simulation and Analysis, ASTM Special Technical Publication 671, pp. 94-117, 1979. Also published as AFML-TR-77-233, February 1978.
R. L. Crane, A. F. Grandt, Jr., and J. P. Gallagher, "Assessment of Flaw Growth Potential in Structural Components," United States Patent No. 4,107,980, August 22, 1978.
J. A. Ori and A. F. Grandt, Jr., “Single-Edge-Cracked Crack Growth Gage,” Fracture Mechanics, ASTM Special Technical Publication 677, 533-549, 1979.
J. P. Hess, A. F. Grandt, Jr., and A. Dumanis, “Effects of Side-Grooves on Fatigue Crack Retardation,” International Journal of Fatigue of Engineering Materials and Structures , Vol. 6, No. 2, 1983, pp. 189-199.
Dumanis and A. F. Grandt, Jr., “Development of a Side-Grooved Crack Gage for Fleet Tracking of Fatigue Damage,” Engineering Fracture Mechanics, Vol. 26, No. 1, 1987, pp. 95-104.
A. Dumanis and A. F. Grandt, Jr., “Development of a Double Crack Growth Gage Algorithm for Application to Fleet Tracking of Fatigue Damage,” Proceedings International Committee on Aeronautical Fatigue 21st Conference, 15th Symposium, Jerusalem, Israel, June 1989.
M. D. Gates and A. F. Grandt, Jr., “Crack Gage Approach to Monitoring Fatigue Damage Potential in Aircraft,” 1997 Society for Experimental Mechanics Spring Conference on Experimental and Applied Mechanics, June 2-4, 1997, Bellevue, Washington (2 pages). Extended version of paper (7 double-column pages) also accepted for publication in the 1997 SEM Spring Post-conference Proceedings, 1998.
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Crack Gage Overview• Crack gage is an “analog computer” that
measures/evaluates severity of structural loading
• Growth of gage crack gives potential for structural crack growth
• Crack gage is a “prognosis sensor”
Adhesive
a S
Crack GageL
a
u
G
Structural Member
LT W
Ps
Ps
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U. S. Patent 4,107,980August 22, 1978
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42Fig. 7.6
Fatigue Crack Retardation(7075-T6 aluminum)
max /min = 18.3/55.2 Mpa max = 99.3 Mpa 1/4001 cycle block
Reference: Bucci, EFM, v 12, No. 3, 1979
No overload
With overload
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Alon Dumanis-ModanEvaluation of the Crack Gage as an Advanced Individual
Tracking Concept, Ph. D. Thesis, Purdue University, Dec. 1982
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Matthew D. Gates A Crack Gage Approach to Monitoring Fatigue
Damage Potential in Aircraft, M.S. Thesis, Purdue University, May 1997.
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Joseph A. OriExperimental Evaluation of a Single Edge Crack Crack
Growth Gage for Monitoring Aircraft Structures, M.S. Thesis, Air Force Institute of Technology, Dec 1977.