fgs general presentation june 2011

8/4/2019 FGS General Presentation June 2011

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The Fatigue Growth Sensor (FGS) System:Background, Improvements, Steps Forward

Prepared By

Non Invasive Technologies, Inc

Los Angeles, CA 90049310-384-2428


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FGS System Background The FGS system is a nondestructive fatigue crack

inspection system.

FGS System includes: twoelectrolyte-filled sensors, aPotentiostat Data Link (PDL), and special software.


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The FGS System - Background Developed in the early 1990s, in part through sponsorship by

the US Air Force.

Internal and external verification (Rockwell Scientific);Validation studies conducted in both laboratory and field(including the AAR FRA TTCI facility).

Can detect cracks as small as 0.001 in. in lab.

Part of SIPS program.

Detects crack growth activity and crack growth precursors.

Adds value to all inspection and predictive maintenanceprograms, as well as provides better information for models.


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Similar to an EKG

Like an EKG:

EKG (electrocardiogram) - a test that records theelectrical activity of the heart, shows abnormal rhythms.

FGS The Fatigue Growth Sensor

Constant voltage applied between structure andelectrode

Current response due to mechanical loading -> FGSsignal

A crack changes how the current flows


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Normal EKG

Abnormal EKG

Normal FGS

Abnormal FGS


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Fundamentals of FGS Uses passivation of the metallic surface to measure

fatigue damage:

Sensor polarizes area, creates passive film.

In growing cracks, cyclic loadingbreaks down passive layer.

Micro-plasticity at crack tip changes amount of exposedmetal.

As new metal is exposed,new, additional passive filmforms which changes FGSsignal.


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The Differential FGS Set-up

An FGS sensor array is applied to an area

of interest and crack detection occurs under

or around the sensor.

The Crack Measurement Sensor (CM) is

placed over the tip of the crack. TheReference Sensor (R) is placed in the same

stress field, but where there is no crack.


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The FGS System Hardware FGS Sensors

Measurement & Reference

Customizable size, shape, geometry

PDL (Potentiostat Data Link).

Precisely controls FGS sensor array voltage

Measures the current flow for the two sensors(indicator of crack condition)

Controls Data Acquisition Rate

Controls Data Collection Times

Stores Data Locally

Wireless and battery powered


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Surface Preparation Sensor Installation Hardware Installation

Wireless Access Point Data Acquisition

Typical Bridge Installation


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Example Installations


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Basics of Data Interpretation Differential FGS used.

Comparison of CM and R Sensors.

Ratio of the CM sensor and R sensor data used as firstdecision metric -> Energy Ratio.

Special software uses specially designed algorithm todetermine growth activity.

Possible Output

No Growth

Microplasticity (Future Initiation)

Active Growth


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The FGS System - Software

Frequency content and

magnitude differencesindicate crack condition.

Algorithm

preliminarilyindicates crackactivity status.

Results = Energy Ratio

No growth


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Predictive Capabilities:Threshold Lab Verifications

Controlled environment

Precise measurements

Dynamic Input

Theoretical comparisons


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Experimental Setup

Crack


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Fatigue Data

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Crack Growth Data

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Fracture Surface


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FGS and Threshold Bridge Loading

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FGS and Threshold

20


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Energy Ratio

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Energy Ratio = Ratio of Areas Under Crack Measurement and

Reference Measurement Curves

Energy Ratio = 1.16

DK = 2.54 ksi in

Energy Ratio = 2.4

DK = 17.25 ksi in


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Improving the Standard of Care Federal Highway Administration -

Reliability of Visual InspectionStudy of 49 State DOT bridge inspectors.

Multiple fatigue crack indications at multiple locations

All at obviously fatigue sensitive locations

Inspectors correctly identified the crack indications lessthan 10% of the time.

That means 90 out of every 100 fatigue cracks aremissed by conventional methods

Also repairs are being made 4 out of 5 times at areaswhich do not require it (80% false positives).


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Frequency Domain Output

Location 1a: No Significant Activity, ER=1.3

Typical Active Sample

Energy Ratio = 3.1


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Predictive information available for fatigue criticallocations.

Integrate with FASTRAN II.

Find hotspots in all structures

Bridges, aircraft, offshore platforms, ships, shipping cranes

Obtain additional, more useful, more accurateinformation for decisions.

Almost immediate repair verification.

Conclusions


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Next Steps for Product Improvement

Shift Focus to 7075 AL.

Polarizing voltage

Threshold correlation curves

Crack growth rate.

Localized excitation method.

Develop fracture mechanics methodology totransfer FGS into FASTRAN based code.

Long term sensor/electrolyte change.


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Approximate Inspection Costs

Costs are based on number of areas to be

inspected.

Inspection crew can cover up to ten cracklocations in one shift, depending on ease of

access.

For a simple two span bridge cost will beapproximately US$15,000.

fgs general presentation june 2011

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