DTIC ADA522795: Structural Health Management in the NAVY

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by  Defense Technical Information Center

Structural Health Management in the NAVY
Ignacio Perez,1,* Michael DiUlio,2 Scott Maley3 and Nam Phan3
1Office of Naval Research, Arlington, VA 22202, USA
2Naval Sea Systems Command, Washington, DC 20376, USA
3Naval Air Systems Command, Patuxent River, MD 20678, USA
There is a critical need for integrated system health management (ISHM) approaches to
asset maintenance. Ideally, ISHM methodologies would track the system usage and the
associated loads, monitor the system degradation and materials state, monitor relevant
environmental parameters and their effects on system degradation, detect insipient
system damage, diagnose failure mode, predict future system performance, and recom-
mend maintenance actions. Even though there has been considerable progress in many
subareasofISHMoverthepastyears,thereisstillampleroomforfutureimprovementsin
all technological aspects affecting ISHM. In fact, progress in ISHM has not been uniform.
Somesubsystemshaveexperiencedafargreaterdegreeofdevelopmentthanothers.For
example,engineandmachineryhealthmonitoringanddiagnostics,duetoitscriticality,has
evolved at a faster pace than structural health monitoring. This article will review some of
theaspectsthatneedtobeaddressedinordertomakestructuralhealthmonitoring(SHM)
ofmilitary systems areality inthe nearfuture.
Keywords integrated condition assessment system (cid:2) comprehensive automated
maintenance environment-optimized (cid:2) sense and response logistics (cid:2) Navy
communities (cid:2) fatigue life expended (cid:2) lifecycle cost.
1 Problem Statement now broadly recognized as being expensive and
unsustainable, especially with regard to the
DoD weapon systems, and especially Navy demands of an increasingly aging fleet. In fact, as
systems, have been designed such that their struc- budgets have been reduced in recent years, some
tures, if properly maintained, will not experience aging asset classes are not being replaced by newer
structural damage (defined as crack initiation) for ones and are therefore being required to operate
the design life of the system. Critical to this design well beyond their original design life. This reality
philosophy is a rigorous maintenance program [1]. makes it ever more important that we explore new
The Navy has accordingly developed a vast main- approaches to asset maintenance.
tenance organization and associated infrastructure There are many points throughout the life
for the sole purpose of assuring fleet readiness. cycle of our systems where the total ownership
This design and maintenance philosophy has cost can be reduced (Figure 1). Better materials
served the Navy well for many years, but it is with improved resistancetodamage areconstantly
(cid:2)TheAuthor(s),2010.Reprintsandpermissions:
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Structural Health Management in the NAVY
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200 StructuralHealthMonitoring9(3)
Maintenance
Minimize will be required
requirements for
maintenance
Minimize
Better materials requirements for Unscheduled events
Corrosion resistant unscheduled will happen
Tougher maintenance
Fatigue resistant
Fire resistant
Mechanics of materials Optimize Parts not
Environmental effects SHM maintenance available
Stress corrosion cracking cycle time
Diagnostics
Corrosion fatigue
Prognostics
Thermo fatigue
CBM
Consumable vs repairable CPI Optimize
CPI Sense and reponse log
up-grades/
Readiness-based sparing
On time supply refurbishments
On site training
Unique ID tagging Obsolescence management
CPI Aging systems
Rapid systems
Rapid prototyping
Reverse engineering, CPI
Figure 1 InreducingsystemLCC,healthmonitoringtechnologiescanassistatmanypointsduringtheusefullifeofthe
component.
being developed to minimize the requirements for centeredonengineandmachinerytracking,andthe
scheduledandunscheduledmaintenance.However, healthandusagemonitoringsystem(HUMS)[3]on
any material system will eventually degrade and most of many Navy helicopters and aircraft) there
maintenancewillberequired.Inordertominimize has been little progress in the area of SHM where
unscheduled maintenance actions, which are the theactualmaterialstateismonitored.
highest cost drivers and readiness degrader in any
fleet, the need for monitoring all systems compo-
2 Why SHM?
nents for health is important. Investments in tech-
nologies such as condition based maintenance
(CBM),structuralhealthmonitoring(SHM),prog- A properly designed SHM system (one that in
nosticsandhealthmanagement(PHM),andothers addition to monitoring loads, also monitored
arecriticaltobotheffectivenessandaffordabilityat actual system degradation through pre-crack incu-
this juncture. But even with improved monitoring bation, nucleation and growth, corrosion detec-
systems, damage will always happen and unsched- tion, and that also monitored relevant
uled maintenance will eventually be required. environmentalparameterssuchascorrosivity,tem-
Therefore it is important to optimize the mainte- perature, altitude, and others, and their effects on
nancecycle by aligning these monitoring technolo- the acceleration of system degradation) could sup-
gieswiththelogistics,operations,andmaintenance port the fleet in many ways beyond just determin-
communities to appropriately and effectively ing the fatigue life expended (FLE) for tracked
respondtotheseevents.Additionalsavingsandeffi- structural components. Some of these added bene-
ciencies can be achieved by optimizing the refurb- fits include:
ishmentsandupgradesasoursystemsapproachthe
endoftheirusefullife.Despitemanyyearsofdevel- . Providingabetterunderstandingoftheresponse
opmentinallthesetechnologies,andsomesuccess- of the structure under real operational condi-
fulimplementationofsophisticatedsystemsaboard tions. This would also allow validation of the
Navyshipsandaircraft(suchastheintegratedcon- structural design throughout the entire life of
ditionassessmentsystem(ICAS)[2]whichismostly the structure.
Perezetal. Structural Health Management in the NAVY 201
. Allowing for more streamlined structural The business case is also intimately tied to the
designs (lighter weight) since the degradation state-of-the-art of the systems used for SHM, fea-
of critical components would be continuously sibility of technology for new capabilities needed,
monitored during the pre-crack incubation the type of information provided, its reliability,
phase, crack nucleation, and slow crack growth and the level of integration provided. This article
phase allowing for their safe removal or recon- will examine some of these factors.
ditioning well before any defect approached its
critical stage.
3.1 Understanding Customer Requirements
. Enhancing confidence levels and reducing oper-
ational risk when introducing new materials, There are many customers in DoD that could
new designs, or new repair concepts into the benefit from an SHM system. These customers
structure [4]. belong to a number of military communities that
. Monitoring stresses on repaired structures and in most cases are not collocated and in some case
the stress redistribution around patches and do not interact directly, but they all have the
repairs. common goal of supporting the war fighter in an
. Facilitating the day-to-day management of the effective and efficient manner. These communities
platform by supporting operational and mainte- include the acquisition community; the require-
nance decisions, especially during a surge situa- ments community; the operations planning com-
tion where resources become limited. munity; the logistics community; the maintenance
. Providing knowledge of where to inspect the community; the design and manufacturing com-
structure when damage develops through envi- munities; the user community, and others. An
ronmental effects or from foreign object SHM system could benefit all these communities
impacts, therefore reducing inspection time and in more ways than one. If we are to implement
maintenance costs. SHM into military systems, a credible business
. Aiding in the decision process of life extension case needs to be articulated to as many of these
programs or sales to commercial companies or communities as possible. The benefits that SHM
foreign governments. could provide to different communities include:
. Providing monitoring capability for damage in
hard to reach areas or inside hidden structures, . Acquisition community – by better asset life
therefore minimizing the need for expensive tracking and long term force planning.
tear-down inspections. . Requirements community – by having more
accurate insight into the true health of existing
Despite all these potential benefits of a perma- weapon systems, and better plan for retirement
nentlyinstalled SHM system, the fact remainsthat ofonesystemandtheacquisitionandfieldingof
few platforms incorporate them into their struc- its replacement system.
tures program. The few that do, limit their use to . Operations planning community – by identify-
loadmonitoringinsupport offatiguelife tracking. ing, and selecting for use, those weapon systems
which require the least amount of structural
3 Obstacles to SHM maintenance activities during the period of
deployment
ArecentpaperbyDerrisoetal.[5]pointedout . Logistics community – by allowing them to
someofthereasonsforsuchalackoffieldedSHM more accurately project out component usage
systems in DoD. The two main reasons were: rates (at an aircraft, squadron, or fleet level)
developingacrediblebusinesscaseandthetechno- and helping them to anticipate replacement
logical feasibility for SHM. Factors that will help rates, stocking requirements, and budget alloca-
create the business case include understanding the tions. This information is of particular impor-
customer needs and requirements and performing tance to the success of PBL contracts.
a credible cost and risk analysis (reliability, . Design and manufacturing community –
maintainability, scalability, and other factors). because the actual response of the system to
202 StructuralHealthMonitoring9(3)
real multi-axial loading conditions (especially ICAS include:
from extreme loading conditions due to maneu-
vering, weather or combat) could be monitored . CDS – A core piece of ICAS is the CDS. Each
and used for future system upgrades or designs. workstation accommodates a unique CDS to
This is especially true for large platforms (ships, identify tolerant and out of tolerant ranges for
subs, tankers, etc.) where full article testing is monitored equipment. The raw data is trended
not possible. and provides plant status information that is
. Maintenance community – could benefit from useful to the operator/maintainer. ICAS also
better prognostics of upcoming structural main- contains links to digital logistic products such
tenance activities for planning their workload. as the engineering operational sequencing
Being aware of developing structural issues system (EOSS), planned maintenance system,
also enables ‘opportunistic’ maintenance, and integrated electronic technical.
where a maintainer could investigate or repair . Manuals – These integrated electronic technical
a detected condition when already working manuals(IETMs)allowformaintenancerecom-
inthatsectionoftheaircraftforotherpurposes, mendations to be linked automatically and
reducing redundant efforts to gain access to directly to the appropriate section or card as
certain areas and increasing maintainer well as browsing the entire library.
efficiency. . Maintenance engineering library server (MELS)
. User community – from increased system avail- – Maintenance engineering library server is a
ability due to more proactive maintenance and common shore side data repository of ICAS
lower frequency of unexpected structural issues data/information where statistical analysis can
which may cause a mission abort, or simply be accomplished to further maintenance savings
make a system nonmission-capable and unable and to gain a better knowledge of equipment
to begin the mission in the first place. operation in a marine environment.
. Integrated performance analysis report (IPAR)
As an example of an integrated system for – Integrated performance analysis report is a
asset maintenance, the Navy has implemented the generated performance analysis report that
integrated condition assessment system (ICAS) on represents the health of monitored shipboard
more than 100 ships [2]. ICAS gathers and pro- systems for a particular ship.
cesses real-time equipment data from system inter- . Enterprise performance analysis report (ePAR)
faces and machinery sensors and periodic data – Enterprise performance analysis report is a
from hand held devices (i.e., palm pilots), for eval- fleet-wide analysis report for a particular
uating the operational condition of monitored system across all ship classes.
equipment. ICAS functionality provides the bene-
fits of time saved over manually collecting and ICAS coupled with distance support (DS 2.0)
analyzing data, of unplanned failure avoidance to enables remote monitoring (RM). In short we are
reduce the occurrence of catastrophic failures and gathering shipboard data, transmitting from
potential secondary equipment damage, of redu- ship-to-shore,generatinghealthassessmentreports
cing unnecessary ‘open and inspect’ and (IPARs) and disseminating that information to
time-directed repairs, and of providing data for maintenance brokers and decision makers, such
failure analysis, expert system alerts, remote assis- as regional maintenance centers (RMCs), port
tance for deployed ships as well as feedback data engineers, CLASSRONs, and the recently created
forRCManalysis.AtypicalUSNavyICASinstal- surface ship life cycle management activity
lation consists of four to five workstations, one in (SSLCM).
each major machinery compartment as depicted in Another system being developed and imple-
Figure2,connectedbyanactivelocalareanetwork mented by the Navy is the comprehensive auto-
(LAN). Each workstation accommodates a unique mated maintenance environment – optimized
configuration data set (CDS), which contains the (CAMEO) system (Figure 3) which is an adapt-
engineering information. The main components of able, open source set of automated logistics
Perezetal. Structural Health Management in the NAVY 203
CCS MER 1 MER 2 AMR 1 CSMC
HP Laserjet 4
HP Deskjet 1200C
Interfaces
Equipment
3M coordinator Sensors DAS-64
SNAP
Expert Data bus DMS/CISE
analysis Interface
Digital
Library Trending Plot logs PDA
ATIS
Maintenance alerts/
advisories PDT
CD-ROM “Juke box”
Figure 2 Typical ICAS installation aboard Navy ships. Each room with an engine (mechanical engineering room
(MER), auxiliarymechanical room(AMR)) has anICAS workstation aswellas thecontrol center(CCS).
environment (ALE) capabilities that support con- . Integrated usage based fatigue tracking (SAFE/
tinuousintegrationandautomationofoperational, FLE) for airframes and life limited dynamic
maintenance, and logistical processes to improve components, providing greatly extended fatigue
aircraft readiness and significantly decrease sus- lives and significant cost avoidance in replace-
tainment costs for the war fighter community [6]. ment parts over the life of the program.
Primary integrated capabilities currently available . Electronic PMIC/parts life viewer which is a
or in development include: dynamicallyupdatedviewofallupcomingmain-
tenance actions on a given aircraft. This allows
. A Type II/Class IV integrated electronic techni- the user to visualize upcoming requirements
cal manual (IETM) providing maintenance and when some of the maintenance requirements
troubleshooting procedures, illustrated parts have changed from a fixed time interval to vari-
breakdown (IPB), electronic wiring suite able usage based actions. This same tool facili-
(EWS), and a number of labor savings capabil- tates the inclusion of and planning for other
ities from integration with the rest of the ALE. CBMþ or SHM health indicators upon which
The current IETM is not S1000D based, but an the maintainer may need to take action.
S1000D version of the IETM is in development. . Automated statistical data mining is also in
. Ground station capabilities to provide conduit development to facilitate detection of meaning-
for post flight download and viewing/analysis fultrendsinrecordeddata,eitheronanindivid-
of aircraft usage data, aircrew debrief, genera- ual aircraft basis over time or by comparing
tion of needed work orders, and automated individual aircraft to others in the fleet. This
transmission of data to/from other information providesthe‘trigger’forengineerstoinvestigate
systems. data of interest and facilitate identification and
204 StructuralHealthMonitoring9(3)
CAMEO operational capability
Maintenance flight debrief
(cid:129) Download/process aircraft flight data
(cid:129) Collect support data (aircraft configuration, NAVFLIR)
(cid:129) Perform calculations (usage, FLE QA)
(cid:129) Review data (maintenance, VSLED, usage)
(cid:129) Identify/enter maintenance actions (work orders)
(cid:129) Archive aircraft flight data package
Base Afloat Maintenance action
(cid:129) Retrieve/distribute work order (s)
MIS (cid:129) Review work order, IETM (IPB, tools, parts), supply
(NALCOMIS/IMDS) (cid:129) Perform maintenance (work order, IETM, supply)
Maintainer
(cid:129) Close work order
CAMEO
PEMA Support activity
Aircrew CAMEO
Detachment Unit Server (cid:129) FLE analysis/SAFE report distribution
(cid:129) Fleet support user access
Maintainer Administration
(cid:129) Aircraft constants upload
CAMEO (cid:129) Aircraft/engine transfer
Aircrew PEMA (cid:129) User, server, PEMA management
NIPRNET/Internet
Fleet support
Fleet support team
WWeebb cclliieenntt users
OEM CAMEO
Fleet support user Training Fleet server
Depot (OSC) Aircraft maintenance
Major commands (AFSOC, MALS, TYCOM) data archive FST engineer
System command (NAVAIR, SAFE, ASIP, MFOQA) Web client
Figure 3 CAMEOarchitecture.
association of trends with known component ashore) and support of USMC enhanced company
failures or detected anomalies. Once a positive operations.TheoverarchingS&RLsystemcompo-
correlation is identified, the specific trend or nents are; a dynamic and real time networked
combination of trends can be incorporated as a situational awareness and knowledge creation
health indicator for display to the operational system for assets ashore, an information architec-
user in future situations. ture that will dynamically acquire, parse, process,
store, distribute, create knowledge, transmit and
Finally, the sense and respond logistics present information in a shared data environment,
(S&RL) program is a 5-year effort sponsored by and predictive and adaptive logistics decision sup-
the Office of Naval Research enabling Logistics port and planning tools to be used to generate
Modernization for the United State Marine courses of support (CoS) and courses of action
Corps. S&RL will invest in science andtechnology (CoA).
(S&T) that will automate the detection and the The S&RL program will also develop a plat-
consumption of logistics resources of a marine form interface prognostic framework that will col-
expeditionary brigade (MEB) ashore in combat lect, interpret, and coordinate health data from
operations. S&RL will also provide automation USMC ground vehicles, to evaluate mission readi-
for logistics planning and assessment, supporting ness, recognize trends of equipment degradation,
thecognitiveprocessesofthelogisticsplanner.Key and predict probabilities of remaining useful life
conceptsofthislogisticstransformationareopera- for vehicle subsystems. The prognostics embedded
tions from the Sea Base (vice the iron mountain health management capability helps fulfill the
Perezetal. Structural Health Management in the NAVY 205
‘objective’requirementtofurtherlocalizethefault/ In determining the cost of the new technology
failuredowntothesubsystemorcomponentlevels. one has to include not only the actual cost of the
In addition to identifying impending failures the separate components, but also the more intangible
systemmustbecapableofestimatingtheplatform’s costs such as the sensor placement studies, surface
capability to perform the next mission. The prog- preparation,installationcosts,costoftrainingper-
nostics embedded health management capability sonneltooperateandmaintainsystem,repaircost,
enables the processing traditionally done centrally sensor removal, and cost of disposal at the end of
in a shared data environment to be distributed to life. In order for the adoption of SHM to be justi-
the platform level. This approach dramatically fied, the sum of these costs should be small and/or
reducesbandwidthrequiredforfrequentdatatrans- the benefits should be substantial. Sensors should
mission without sacrificing the ultimate fidelity of have low cost with minimal or no maintenance
theshareddataenvironment.Situationalawareness requirements over the life of the platform, with
ateverylevelofthehierarchyisimprovedbyremov- high reliability and no false calls. Probably the
ingdependenceonanupstreamanalysis. toughest challenge is demonstrating reliability of
the SHM system so that the system itself does
3.2 Cost Analysis not become a maintenance driver and reducer of
weapon system availability.
In addition to understanding the customer
needs and requirement, it is important to provide
a credible cost/benefit analysis that can be used to 3.3 Technology Maturity
decide if it is worth investing in the new technol-
Ultimately what defines SHM technology
ogy. Superficially, at least in the case of the Navy,
maturityisitsreliabilityintermsofboth,thehard-
itmightappeartobedifficulttoprovideacredible
ware used and the information provided in the
costbenefitjustificationfornewSHMtechnologies
appropriate operational environment. In general,
since Naval weapon systems are designed so that
the hardware needs to be robust, durable, light
their structures will not crack or corrode through-
out their entire life if properly maintained and weight, with small footprint, and with minimum
operated. Put in simple terms, Naval structures power and wiring requirements. With respect to
are designed so that they will not damage over the reliability of the information provided by the
their life time, therefore why monitor them? That SHM system, reliability needs to be quantified in
is, there is no clear benefit, but there are clearly terms of the probability with which a given SHM
added costs. The key assumption is ‘if properly system will detect a pre-specified defect with a
maintained and operated’. The fact is that despite given confidence level. It is very difficult to specify
all of our design conservatism, maintenance infra- thelevelofmaturityofSHMtechnologyingeneral
structure, and safe operational envelopes, damage terms because it depends on many factors such as
in the form of cracks and corrosion does happen. theSHMmodalitybeingused(seeTable1),onthe
Mission changes, weather effects, combat opera- sensorsandtransducers used,onthetypeofdefect
tions, overloads, design modifications, repairs, beingsought,anditslocationrelativetothesensor
hard landings, material variability, design errors, nodes,onthestructuralmaterialsbeingmonitored,
and a multitude of other controllable and uncon- on the environmental condition and on the
trollablefactorsovercomeourbesteffortstoavoid required metrics for success. For example, below
damage. Therefore, in developing the cost/benefit are a few parameters that could render a mature
analysis it is important to document as accurately technology immature:
as possible the actual inspection hours and cost,
maintenance hours, repair intervals, mission and . The parameters being monitored could be of a
readiness impact history, number of defects and global nature (velocity, altitude, acceleration,
defect types. This will provide a solid baseline to outside temperature, and humidity) or a local
compare with new technology in terms of cost and nature (stress at key structural points, corrosiv-
operational benefits. ity at specific location);
206 StructuralHealthMonitoring9(3)
Table 1 SHMmodalityoptions.Ingeneral,anoptimalSHMmodalitywillliesomewhere
in betweenthe twocolumnsshown inthistable.
Mechanical modeling Physical sensors
Global monitoring Local monitoring
Known damage site Unknown damage location
Passive sensors Active monitoring
Long term monitoring (cradle-to-grave) Short term monitoring
Battery operated Energy harvesting
Off-board data management On-board data management
Model based analysis Model independent methodologies
Wired sensors Wireless sensors
Fixed sensor network Scalable architecture
Permanently installed Removable sensors
Mechanically fastened Adhesively mounted
Continuous monitoring Intermittent monitoring
Data centrally stored Data stored locally
Sensors inside the structure Outside the structure
Repairable sensors Redundant sensors
Static (quasistatic) signals Dynamic signal monitoring
Surface Mounted Embedded
. The phenomena being monitored could be of a for instance an SHM system that passively sought
static nature (such as cracks and corrosion) or dynamic signatures from hidden point sources of
dynamic (such as impact event, wave slamming, unknown origin using wireless technology.
flutter, acoustic emission); Unfortunately, it is the later system, the one that
. Damagelocationscould beknown(fromhistor- would be more desirable since cracks have a habit
ical trends, components critical loading path) or of appearing when least expected, hidden from
unknown (corrosion, paint degradation, view or in unexpected locations and we cannot
cracking); afford to instrument the entire platform with
. Damages could be surface breaking (surface sensors.
cracks, paint discoloration) or subsurface and
hidden from view (second layer cracks, hidden
4 Summary
corrosion);
. Interrogation methods could be active
The Navy, for the most part, manages the
(acousto-ultrasonic, eddy current) or passive
(AE monitoring, environmental excitation); health of its structures by using safe life principles.
. Sensors used could be wired or wireless. Structures and components are retired well before
cracks initiate (defined as a 10 mil crack) as deter-
Other factors that will affect the level of mined from full scale or component fatigue test.
maturity of a specific SHM modality are listed in Large factors of safety are introduced to account
Table 1. for material property variability, environmental
The only broad SHM technology maturity variability,andassumptionsmadeintheanalytical
statement that can be expressed is that the SHM models used to estimate time to crack initiation.
modalitiesshownontheleftcolumnofTable1are The Navy uses the FLE as the main parameter to
(for the most part) more mature than those on the determine asset retirement time. This requires
right column. Therefore an SHM system that real-time tracking of the loads experienced by the
sought to perform global monitoring of static or structure, which the Navy accomplishes by using a
quasistatic parameters, looking for surface break- few sensors (accelerometers, strain gauges) and
ingdamageinknownlocations,andthatuseactive parametric data combined with sophisticated
interrogation methods with wired sensors would global models of the mechanical response of the
have far more mature technologies available than structure. This approach has served the Navy
Perezetal. Structural Health Management in the NAVY 207
well as demonstrated by low historical failure rate References
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