Effective State Awareness Information is

Enabling for System Prognosis

Mark M. Derriso

Advanced Structures Branch

Air Vehicles Directorate

Air Force Research LaboratoryWorkshop on Prognosis of Aircraft and Space

Devices, Components, and SystemsFebruary 19-20, 2008 – Cincinnati, OH

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Overview

Workshop Topics: “…In the future, the USAF would like to develop

state awareness monitoring capabilities that could enable accurate prediction of the remaining service life and future performance capability of critical components as well as be used to take specific corrective actions to assure mission completion and minimize operating cost and risk.”

This is Integrated Systems Health Management!

Determine Ability to Perform MissionDetermine Ability to Perform Mission

Assess DamageAssess Damage

Detect DamageDetect Damage

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Critical ComponentsMeasurands

Structural Health Management

Controls Health Management

Engine Health Management

Electronics Health Management

Sub-systems

HM Data

HM Data

HM Data

HM Data

Multiple 0.02 inchCracks in fuselage

Flight Control Actuator

Frozen at 20 degrees

Bearing Spalling

LRU is Malfunctioning

Data Analysis Damage

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System Performance

Multiple 0.02 inchCracks in fuselage

Flight Control Actuator

Frozen at 20 degrees

Bearing Spalling

LRU is Malfunctioning

Data Analysis Vehicle-Level Health Status

Alt

itu

de

Mach

CL max

T max

q max

System Performance Bounds

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Airframe Design

MATERIAL STRUCTURE(Device, Component, or System)

Materials ProcessingManufacturing

Materials PropertiesLoads, Boundary Conditions,

Operational Environment

UNCERTAINTYassociated with each of these

areas that propagates through to the system level

Uncertainty_Total = U_material + U_manufacturing + U_operational

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Design for UncertaintySafe-life design

The Safe-life design technique is employed in critical systems which are either very difficult to repair or may cause severe damage to life and property. These systems are designed to work for years without requirement of any repairs.

Damage-tolerant design

Damage-tolerant is the property that enables a system to continue operating properly in the event of the failure of (or one or more faults within) some of its components. If its operating quality decreases at all, the decrease is proportional to the severity of the failure

F-4 F-16

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Failure Mode, Effects, & Criticality Analysis (FMECA)

FMECA The objective of FMECA is to

identify the components of products and systems most likely to cause failure, so that these potential failures can then be designed out.

FMECA allows the identification early in the product development process of potential problems or safety hazards which are inherent in a product design.

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V&V of Airframe DesignStructural Design

Full- Scale Fatigue Testing

Problem Areas Identified

Front Spar

Main Spar

Rear Spar

Closure Spar

F-15 Wing

Conduit Hole (hot spot)

Inspection Schedule Constructed

Airframe Prognosis: No Failures Throughout Design Life

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Airframe Prognosis

However, requirements changes Vehicles asked to perform different missions Vehicles modified to fulfill new purposes Vehicles asked to serve past original design life

What is the prognosis then?

Vehicle prognosis based on airframe prognosis

1111

Operational UncertaintyOperational Uncertainty

External LoadingExternal Loading maneuvers, gusts, taxi-loadsmaneuvers, gusts, taxi-loads

Internal LoadingInternal Loading bending, torsion, shearbending, torsion, shear

Environmental ConditionsEnvironmental Conditions temperature, humiditytemperature, humidity

All are Factors the Effects Fatigue Life

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State Awareness

State awareness refers to knowledge regarding the current condition or capability

For airframe subsystems, state awareness is from the diagnostic portions of the structural health monitoring (SHM) system which detect, localize and assess any damage

State awareness allows subsystem prognosis which enables overall system prognosis

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Definition of SHM

SHM refers to automated methods for determining adverse changes in the integrity of mechanical systems

SHM system capability is typically broken into the following levels of increasing difficulty: damage detection damage localization damage assessment life prediction

diagnosis

prognosis

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SHM Development Process

Identify Item of Interest

Identify Relevant Failure Modes of Item– Dependent on operating environment

Characterize Failure Modes that Result in System Degradation

– Identify physics of degradation mechanisms – Identify precursors that indicate imminent degradation– Identify mechanisms which can be sensed and are

correlated to system degradation

Design Sensor System to Capture Degradation

Mechanisms– Direct, inferred, virtual– On-board, off-board

ComponentLevel

ReasonerObtain Initial Sensor Output

Real Time and

Updated Sensor Output

Assess Current State of Component

Predict Remaining Capability– Assumed operating conditions

Output to SystemLevel Reasoner

Identify Item of Interest

Identify Relevant Failure Modes of Item– Dependent on operating environment

Characterize Failure Modes that Result in System Degradation

– Identify physics of degradation mechanisms – Identify precursors that indicate imminent degradation– Identify mechanisms which can be sensed and are

correlated to system degradation

Design Sensor System to Capture Degradation

Mechanisms– Direct, inferred, virtual– On-board, off-board

ComponentLevel

ReasonerObtain Initial Sensor Output

Real Time and

Updated Sensor Output

Assess Current State of Component

Predict Remaining Capability– Assumed operating conditions

Output to SystemLevel Reasoner

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Understand the structure.

Understand available

technologies and methods.

Develop system-level SHM

requirements.

Develop candidate SHM system

designs.

Develop potential benefits for

applying SHM.

Compare each design to the requirements.

Understand the costs of the SHM

systems.

Does the design meet the

requirements?

Remove the design from

consideration.No

Yes

Implement the lowest cost SHM system design.

Structural design

SHM Development Framework

Requirements and knowledge of structural

behavior and loads

Sensing technology and sensing system design+

SHM System Design

Ultrasonic wave propagation model

Damage detection sensor

Maintenance Benefit

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State Awareness Architecture

MeasurandsData

AnalysisReasonin

gProcess

Experience&

Knowledge

Predictions(physics-based models,

trending)

Current State Information

The Real World

Based on Col Boyd’s OODA Loop

Loads, damage, etc..

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The ISHM Goal

“I don't care about what anything was DESIGNED to do, I care about what it CAN

do”.