Transcript Slide 1

Challenges Associated with Implementing
an Integrated Structural Health/Life
Management System for Aerospace
Structures
J.P. Gallagher
Consultant
Retired ASC/EN, USAF
937-848-4372
[email protected]
Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08
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Integrated Structural Life Monitoring
On-Board
Usage Monitoring
Structural
Modelling
(operational parameters)
Aging
Damage
Monitoring Actual State
of Aircraft
Structural
Health
Off-Board
Damage Monitoring
(inspection results)
On-Board
Damage Monitoring
(damage event sensors)
Integrated
Airframe Monitoring
(combined usage estimates
of damage &
observed damage)
Prognosis (assessments or
predictions) can take place
on-board or off-board
Ref: J.P. Gallagher et al., “Future Airframe Lifing Methods”, NATO AVT-125 report, RTO,, in press (2008)
Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08
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Challenges for On-board Sensing
• Cracking in safety-of-flight critical structure typically occurs later
in the airframe life, so on-board systems must last for the
airframe’s lifetime (20-40 years)
• Airframe inspection system reliability is less than anticipated for
multiple reasons - on-board systems may solve some issues
• The key to success – must have accurate and reliable
models/systems for anticipating “surprises”
– Unconservative answers cause structural losses
– Can not cry wolf when no wolf exists
• Usage monitoring suffers due to lower budget priorities for
upgrading/replacing equipment required to collect operational
parameters that affect damage evolution
Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08
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Cracking Damage Counts
The Crack Size Population & Its Contributing Elements Evolve with Time
Freq.
Typical Material and
Manufacturing
Defects
Service Induced
Defects, caused
by other damage
mechanisms
Abnormal
Material and
Manufacturing
Defects
Size of Defect (at some time, T)
High end, rare
damage
dictate
structural
maintenance
for safety
The bigger cracks in the population are those that are most likely to cause
premature structural failure & dictate when maintenance action is required
Ref: J.P. Gallagher, ICAF 2007
Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08
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Rogue Damage Does In Fact Exist
Comparing Observed Damage to Anticipated Damage
0.6
Cracks found during Inspections
Crack Size (inch)
.
0.5
Rogue defects
X
0.4
0.3
Design assumption –
growth from rare
event (10-7)
0.2
0.1
Typical Safety
Design assumption
for cold worked hole
X
0
0
2000
4000
6000
8000
10000
12000
Flt Hrs
Evidence that bigger (rogue) cracks do exist comes from comparison of crack
findings to anticipated crack growth life curves for each FCL
Ref: J.P. Gallagher, ICAF 2007
Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08
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Challenges for Interpreting Sensor Info
• Damage in older aircraft systems does not always occur
where it was anticipated nor according to the design
scenario
• Cracking in lug regions found
on F-22 FSFT
Ref: Gen C.D. Moore, 2007 ASIP
Conference
• These locations are
considered “hot spots.”
Where else might cracking occur that was not
observed on the FSFT? Will the cracking
observed in service have the same characteristics
as that of the FSFT?
Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08
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Concluding Remarks
• Structural health/life monitoring - a key component of Aircraft
Structural Integrity Program (ASIP*) and the integrated
structural health/life management system
– Problem: Lack of attention to executing ASIP requirements and
evaluating structural cracking problems
– Cause: Priorities (capabilities vs. sustainment) and budget pressures
– Result: Unanticipated loss in availability, aircraft groundings, higher
sustainment costs (structural “surprises”)
• Recommendations for Targeted Action:
– Ensure an integrated structural life monitoring capability plan
supports the structural health/life management system
– Demonstrate assessment and prediction via on-board hot spot
sensors
* See references for more detail on ASIP and its applications for sustainment
Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08
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References
1.
2.
3.
4.
5.
Department of Defense Standard Practice, Aircraft Structural Integrity
Program (ASIP), MIL-STD-1530C, 1 Nov 2005.
J.P. Gallagher, “A Review of Philosophies, Processes, Methods and
Approaches that Protect In-Service Aircraft from the Scourge of
Fatigue Failures,” Proceedings of the 24th ICAF Symposium 2007,
Naples, IT (May, 2007).
L.M. Butkus, et al., “U.S. Air Force Efforts In Understanding And
Mitigating The Effects Of “NDI Misses,” Proceedings of the 24th ICAF
Symposium, Naples, IT (May, 2007).
J.P. Gallagher, et al., “Demonstrating the Effectiveness of an
Inspection System to Detect Cracks in Safety of Flight Structure,”
Proc. of the 10th DoD/FAA/NASA Aging Aircraft Conference, Palm
Springs, CA (April, 2007)
J.P. Gallagher, “Damage Tolerant Aircraft Design and its Relationship
to Inspections,” Presentation at the G.R. Irwin Memorial Conference,
U. of Maryland, College Park, MD (March, 2007).
Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08
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