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Microbolometer Thermoelastic Evaluation (MiTE) – Evolution of a Cracking ASI

Management Tool

Nik Rajic & Chris Brooks

Airframe Diagnostic Systems

Aircraft Health & Sustainment Branch

© 2016 Australian Defence Science and Technology Group

2

UNCLASSIFIED – cleared for public release

Outline

ASI dividends from MiTE

– Evolution of a transformative capability for ASI management

The next installment

– A new experimental capability for automated crack detection and crack-growth monitoring.

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UNCLASSIFIED – cleared for public release

Separating FEM Fiction from FEM Fact

Finite Element Modelling (FEM) underpins airframe certification/lifing but has a patchy record on predicting failure in FSFT’s, e.g. F-35 – Prediction based on assumptions, assertions and approximations.

Validation relies on strain gauge (SG) readings – SGs provide limited measurements, and

– never in high stress gradient locations where fatigue normally initiates.

Full-field stress imaging is the answer (can resolve stress-gradients) but – Digital image correlation (DIC) not sensitive enough

– Electronic speckle pattern interferometry not robust enough

– Photoelasticity impractical

– Thermoelastic stress analysis (TSA)

Measuring temperature gets you stress

Temperature variations are small – 3 mK/MPa.

For 30 years conventional wisdom said only cooled photon infrared detectors were up to the job.

Expensive and bulky – major deterrents

)( 321 KT

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UNCLASSIFIED – cleared for public release

Evolution of a Transformative Capability

1982 2005 1993

1995

Commercial

release of

SPATE begins

the modern TSA

era (Ometron,

U.K.)

DSTG unveils

FAST - the first

TSA system to use

a staring-array

detector.

Commercial release

of a staring-array

based system called

DeltaTherm (Stress

Photonics Inc., USA)

DSTG develops

MiTE, the first

thermal detector

based TSA system.

ASI use of TSA

accelerates.

Photon detector era (TSA technology bulky and expensive …. primarily an R&D

instrument)

Thermal detector era (TSA transformed into a low cost, miniature, and robust engineering tool

….. stress imaging everywhere all the time!)

5

UNCLASSIFIED – cleared for public release

Evolution of a Transformative Capability

1982 2005

1993 1995

Commercial

release of

SPATE begins

the modern TSA

era (Ometron,

U.K.)

DSTG unveils

FAST - the first

TSA system to use

a staring-array

detector.

Commercial release

of a staring-array

based system called

DeltaTherm (Stress

Photonics Inc., USA)

DSTG develops

MiTE, the first

thermal detector

based TSA system.

ASI use of TSA

accelerates.

Photon detector era (TSA technology bulky and expensive …. primarily an R&D

instrument)

2008

In situ TSA

pioneered on

F/A-18 centre

barrel FSFT

Thermal detector era (TSA transformed into a low cost, miniature, and robust engineering tool

….. stress imaging everywhere all the time!)

6

UNCLASSIFIED – cleared for public release

Evolution of a Transformative Capability

1982 2005

1993 1995

Commercial

release of

SPATE begins

the modern TSA

era (Ometron,

U.K.)

DSTG unveils

FAST - the first

TSA system to use

a staring-array

detector.

Commercial release

of a staring-array

based system called

DeltaTherm (Stress

Photonics Inc., USA)

DSTG develops

MiTE, the first

thermal detector

based TSA system.

ASI use of TSA

accelerates.

Photon detector era (TSA technology bulky and expensive …. primarily an R&D

instrument)

2008

In situ TSA

pioneered on

F/A-18 centre

barrel FSFT

Largest ever in

situ full-field

stress survey

of an airframe,

F-35A (AJ1)

2015

MiTE

demonstrated

on F-35C &

then F-35B

FSFTs

2014

Thermal detector era (TSA transformed into a low cost, miniature, and robust engineering tool

….. stress imaging everywhere all the time!)

7

UNCLASSIFIED – cleared for public release

Evolution of a Transformative Capability

1982 2005

1993 1995

Commercial

release of

SPATE begins

the modern TSA

era (Ometron,

U.K.)

DSTG unveils

FAST - the first

TSA system to use

a staring-array

detector.

Commercial release

of a staring-array

based system called

DeltaTherm (Stress

Photonics Inc., USA)

DSTG develops

MiTE, the first

thermal detector

based TSA system.

ASI use of TSA

accelerates.

Photon detector era (TSA technology bulky and expensive …. primarily an R&D

instrument)

2008

In situ TSA

pioneered on

F/A-18 centre

barrel FSFT

Largest ever in

situ full-field

stress survey

of an airframe,

F-35A (AJ1)

2015

MiTE

demonstrated

on F-35C &

then F-35B

FSFTs

2015 2014

HOWSAT - first

TSA scan of a

full-scale aircraft

composite

structure

Thermal detector era (TSA transformed into a low cost, miniature, and robust engineering tool

….. stress imaging everywhere all the time!)

8

UNCLASSIFIED – cleared for public release

Evolution of a Transformative Capability

2015

Miniaturised

autonomous stress

imaging cores –

proof of concept

established – world

first

1982 2005 1993

1995

Commercial

release of

SPATE begins

the modern TSA

era (Ometron,

U.K.)

DSTG unveils

FAST - the first

TSA system to use

a staring-array

detector.

Commercial release

of a staring-array

based system called

DeltaTherm (Stress

Photonics Inc., USA)

DSTG develops

MiTE, the first

thermal detector

based TSA system.

ASI use of TSA

accelerates.

Photon detector era (TSA technology bulky and expensive …. primarily an R&D

instrument)

2008

In situ TSA

pioneered on

F/A-18 centre

barrel FSFT

Largest ever in

situ full-field

stress survey

of an airframe,

F-35A (AJ1)

2015

MiTE

demonstrated

on F-35C &

then F-35B

FSFTs

2015 2014

HOWSAT - first

TSA scan of a

full-scale aircraft

composite

structure

Thermal detector era (TSA transformed into a low cost, miniature, and robust engineering tool

….. stress imaging everywhere all the time!)

9

UNCLASSIFIED – cleared for public release

Looking Ahead

2005

Thermal detector era (TSA transformed into a low cost, miniature, and robust engineering tool

….. stress imaging everywhere all the time!)

2015

Miniaturised

autonomous stress

imaging cores –

proof of concept

established

Future FSFT

programs will

probably look

something like

this

DSTG develops

MiTE, the first

thermal detector

based TSA system.

ASI use of TSA

accelerates.

Historical record of stress state. Continuous real-time trend analysis - detection

of load path variations, crack growth tracking etc.

201?

miniMiTE stress imaging

core (wireless comms.)

miniMiTE network accessible via tablet or smart phone

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UNCLASSIFIED – cleared for public release

Crack Detection & Crack Growth Monitoring

Automated crack

detection and

crack growth

monitoring

2005

Thermal detector era (TSA transformed into a low cost, miniature, and robust engineering tool

….. stress imaging everywhere all the time!)

2015

Miniaturised

autonomous stress

imaging cores –

proof of concept

established

DSTG develops

MiTE, the first

thermal detector

based TSA system.

ASI use of TSA

accelerates.

2016

𝜎𝑏 = 𝜎1 + 𝜎2 =2𝐾𝐼

2𝜋𝑟cos

𝜃

2−

2𝐾𝐼𝐼

2𝜋𝑟sin

𝜃

2

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UNCLASSIFIED – cleared for public release

CGM - State of the Art

Current Crack Growth Monitoring Technologies

• Travelling Microscope

• Needs polished surface

• Hard to automate

• Compliance method

• Readily automated

• Calibration required – standard specimens

• Infers crack length, does not measure

• Average crack length not crack tip position

• PD methods

• As for Compliance

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UNCLASSIFIED – cleared for public release

𝜎𝑏 = 𝜎1 + 𝜎2 =2𝐾𝐼

2𝜋𝑟cos

𝜃

2−

2𝐾𝐼𝐼

2𝜋𝑟sin

𝜃

2

1. Thermoelastic response is a function of the effective stress intensity factor

2. Signal peak is at the crack tip

CGM using Thermoelastic Response Measurements

Can (i) locate a crack tip and (ii) determine effective stress intensity factors

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UNCLASSIFIED – cleared for public release

A Fully Automated System

microbolometer

vertical

stage

horizontal

stage

edge-notched

coupon

microscope load signal Infrared data

Correlate data

Detect Crack Tip

Move Stages Image Crack

Tip

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UNCLASSIFIED – cleared for public release

Comparison to Visual Tracking

10mm

5mm

10mm

5mm

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.080

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

TSA (m)

Vis

ua

l (m

)

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UNCLASSIFIED – cleared for public release

Crack Growth Rate

10-8

10-7

10-6

10-5

10-4

10-3

da

/dN

(m

/cycle

)

Visual TSA

ΔK (MPa m)10

110

2

10-9

10-8

10-7

10-6

10-5

10-4

10-3

da

/dN

(m

/cycle

)

Visual TSA

ΔK (MPa m)10

110

2

10-9

10-8

10-7

10-6

10-5

10-4

10-3

da

/dN

(m

/cycle

)

Visual TSA

ΔK (MPa m)10

110

2

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UNCLASSIFIED – cleared for public release

Advantages

Full automation

No polishing

No calibration

No geometry limits

Can be applied to real structure

Profiling of the crack front – i.e. tunneling

Effective stress intensity factor

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UNCLASSIFIED – cleared for public release

Questions?

MiTE Freeware available at: http://www.dsto.defence.gov.au/opportunity/mite