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Improving In-Service Inspection of Composite Structures

CACRC Inspection Task Group Update Application of Advanced NDI to Composite NDI

Improving In-Service Inspection of Composite Structures

CACRC Inspection Task Group Update Application of Advanced NDI to Composite NDI

All rights reserved. Disclosure of this document or any part thereof

to third parties or the use of any information therein is not permitted

except with prior written permission from the author or Sandia Labs.

Dennis RoachSandia National Labs

FAA Airworthiness Assurance Center


ITG Team ParticipantsITG Team Participants

CACRC Inspection Task Group Members:

John Hewitt – Airbus (Co-chair)

Jim Hofer - Boeing

Jeff Kollgaard – Boeing

Kirk Rackow - Sandia Labs AANC

Dennis Roach - Sandia Labs AANC (Co-chair)

Glae McDonald - US Airways

Darrell Thornton – UPS

Richard Watkins - Delta Air Lines

Bob Stevens – United Airlines

Eric Bartoletti – American Airlines

Alex Melton - Northwest Airlines

Ana Tocalino - Embraer

Dave Galella, Al Broz, Rusty Jones, Larry Ilcewicz – FAA


• Industry wide NDI Reference Standards

– Complete (SAE ARP5506 & 5507; DOE report distributed

in June 2004)

• NDI Assessment: Honeycomb Structures

– Experiments completed in early 2007

– DOT report in progress

• NDI Assessment: Solid Laminate Structures

– In process (specimen fabrication completed; exp.

protocols & final implementation planning remains)

• Miscellaneous Ongoing and Planned Studies

– Detection and quantification of weak bonds

– Affect of porosity, repairs & other impediments on NDI

– As required to support main tasks

– Can be initiated to support other task groups

CACRC Inspection Task Group ActivitiesCACRC Inspection Task Group Activities


Composite Inspections &

Reference Standards

Composite Inspections &

Reference Standards

• Industry-wide composite reference standards developed to support damage assessment & inspection

• SAE Aerospace Recommended Practices (ARP 5605 & 5606) - adopted into Boeing and Airbus NDT Manuals

• Improve inspections of composite structures via introduction of advanced NDI methods

• Provides consistent approach to composite inspections - harmonized approach by OEMs worldwide

Optimized NDT

Reference Standards

Composite Structures on Boeing 787 Aircraft


Goals of Composite Honeycomb

Flaw Detection Experiments

Goals of Composite Honeycomb

Flaw Detection Experiments

1) how well current inspection techniques are able to reliably find flaws in composite structures

2) the degree of improvements possible through the integration of more advanced NDI techniques and procedures.

Utilize airline inspectors to establish industry-wide performance curves that quantify:

• Statistically relevant and realistic flaw profiles

• Blind application of techniques to study hits, misses,

false calls, and flaw sizing


What typ

e of flaw

s can

we expe

ct to find

?Myriad of Tap

Test Devices

Tap Testing at Maintenance DepotsTap Testing at Maintenance Depots


Boeing Manual Tap HammerAirbus Manual Tap Hammer

S-9 Sondicator (LFBT)V-95 Mechanical Impedance Analysis

Conventional NDI Devices


Wichitech Digital Tap Hammer

Mitsui Woodpecker withDigital Readout

Automated Tap Test Devices

CATT Instrumented

Tap Test System


CATT Results on 6 Ply Fiberglass

0.25 1

1.75

2.5

3.25 4

4.75

5.5

6.25 7

7.75

8.5

9.25

10

10.75

11.5

12.25

13

13.75

14.5

15.25

16

16.5

15.75

15

14.25

13.5

12.75

12

11.25

10.5

9.75

9

8.25

7.5

6.75

6

5.25

4.5

3.75

3

2.25

1.5

0.75

in.

in.

0.00-0.18

0.18-0.36

0.36-0.54

0.54-0.72

0.72-0.90

0.90-1.09

1.09-1.27

1.27-1.45

1.45-1.63

1.63-1.81

Missed

Missed


Thermography

MAUS

System

SAM System

Shearography

Wide Area and C-Scan Inspection MethodsWide Area and C-Scan Inspection Methods

PE Phased Array UT

UT Wheel Array

UltraImage Scanner


MAUS

Image

Shearography

(LTI) Image

Ultrasonic Wheel Array

SAM Image

Thermography

(TWI) Image


Implementation of Honeycomb

Flaw Detection Experiment

Implementation of Honeycomb

Flaw Detection Experiment


Airlines, 3rd Party Maintenance and Adv.

NDI Organizations Who Have Participated

Airlines, 3rd Party Maintenance and Adv.

NDI Organizations Who Have Participated

Laser UT (Lock.-Martin)

Computer Aided Tap Tester (ISU)

Microwave Scanner (Evisive)

Thermography (TWI - 2)

Laminography (Digiray)

Shearography (LTI)

Air Coupled UT (ISU)

Structural Anomaly Mapping (Honeywell)

MAUS MIA & Resonance Scanner (Boeing)

Digital Radiography (Digiray)

Phased Array Ultrasonics (NDT Sol’ns)

Acoustography (Imperium)

Terahertz (GMA)


Cumulative PoD - Woodpecker for All Panel Types

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5 3

Flaw Size (Dia. in Inches)

Probability of Detection

3 Ply Fiberglass


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5 3



3 Ply Fiberglass 3 Ply Carbon


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5 3



3 Ply Fiberglass 3 Ply Carbon 6 Ply Fiberglass


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5 3



3 Ply Fiberglass 3 Ply Carbon 6 Ply Fiberglass 6 Ply Carbon


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5 3



3 Ply Fiberglass 3 Ply Carbon 6 Ply Fiberglass 6 Ply Carbon 9 Ply Fiberglass


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5 3



3 Ply Fiberglass 3 Ply Carbon 6 Ply Fiberglass 6 Ply Carbon 9 Ply Fiberglass 9 Ply Carbon

Performance of Single Device (Woodpecker)

Over Range of Test Specimen Types

Performance of Single Device (Woodpecker)

Over Range of Test Specimen Types


Performance of Multiple Devices for

A Single Type of Test Specimen

Performance of Multiple Devices for

A Single Type of Test Specimen

Cumulative PoD of All Conventional NDI Devices for 3 Ply Fiberglass

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5 3



Airbus Tap Hammer Boeing Tap Hammer LFBT MIA Wichitech DTH Woodpecker


Conclusions – Composite Honeycomb NDIConclusions – Composite Honeycomb NDI

� 90% POD is not achieved for 1” dia. flaws; at 9 plies it exceeds 2” dia.

�Human factors issues (time, attention to detail, proper deployment)

�Some inspectors marked grids on panel to aid in coverage of inspection

area – most inspectors had good coverage; some followed random

pattern (find small flaws but miss large ones)

�Overall, MIA mode worked well (reliability, repeatability, ease of use)

How are we doing? – Flaw Detection with Conventional NDI

� Improvement in flaw detection ranged from 66% to 72%

� Automated deployment & data presentation/analysis reduces many

human factors concerns (100% coverage; flaw recognition on images)

� Allow for more rapid inspections

� MAUS, Thermography (sizing), Shearography all performed well

How can advanced NDI help? – Flaw Detection with More Sophisticated NDI


Purpose

• Determine in-service flaw detection capabilities: 1) conventional NDT

methods vs. 2) improvements through use of advanced NDT.

• Optimize laminate inspection procedures.

• Compare results from hand-held devices with results from scanning

systems (focus on A-scan vs. C-scan and human factors issues in

large area coverage).

• Provide additional information on laminate inspections for the

“Composite Repair NDT/NDI Handbook” (ARP 5089).

An Experiment to Assess Flaw Detection

Performance in Composite Laminate Structures

An Experiment to Assess Flaw Detection

Performance in Composite Laminate Structures

A380 Section 19

737 Composite Horiz. Stabilizer


Specimen Set - Flaw Detection in

Solid Laminate Composites

Specimen Set - Flaw Detection in

Solid Laminate Composites

Thickness Range:

12 – 64 plies


Thick Laminate With Simple TaperThick Laminate With Simple Taper

Type 2 Specimen

.50"

2.00"

2.00"6.00"

10.00"

19.00"38.00"

22.00"

.625"

8.50"

4.125"

9.75"

5.50"

3.16"

3.50"

.625"

4.125"

38.00"

24.75"

3.19"

2.00" X 2.00" X .125" 6X

20 PLY

20 PLY

12 PLY

12 PLY

32 PLY

32 PLY

.50" STEP

.50" STEP

TYP

0 90

PLY ORIENTATION

UPPER

LOWER

1.50"

9.00"

3.50"

1.50" X 10.00" X .225" THK4X

(AIRBUS)

3.19" X 9.00" X .080" THK2X

(BOEING)


Composite Laminate FabricationComposite Laminate Fabrication


Contoured Test Panel with HoneycombContoured Test Panel with Honeycomb

18.00"

2.00"

6.00"

15.00"

20 PLIES(OR AS RECEIVED

PRE-MANUFACTUREDPARTS)

4.00"

2.50"

7.00"

2.50"

3.00" R

FLUSH HEAD FASTENER JOINT

FLAWS TO BE LOCATED INSEPARATION REGIONS (4X)

.250" THICK HONEYCOMB

INITIAL CURE: 85PSI

SEALED & FASTENED AFT SPAR

TAPER OF 10:1

FLUSH HEAD FASTENER JOINT

24 PLIES


Contoured Test Panel - FabricationContoured Test Panel - Fabrication

Flaws in Aft Spar

Concentric FBH to

Simulate Impact Damage


• Surface area & no. of flaws req’d (no. of specimens)

vs. time for inspector to complete experiment

� Trial inspections on simulated stabilizer by UA

inspectors – 2.9 to 3.9 ft.2 per hour

Experiment Design & ImplementationExperiment Design & Implementation

Simulated Vertical Stabilizer with Stringers, Rib Sections and Engineered Flaws

Three stringer-to-skin disbonds (yellow)

Two rib to-skin-partial disbonds (blue)


Phased Array UT Inspection of Vertical Stabilizer Specimen

United Airlines

inspection with hand-

held P-E UT

MAUS – Resonance Mode


• Process control alone may not ensure satisfactory bond

strength

• Must consider joint degradation - environmental effects of

moisture, aging, stress, fatigue

• Method must be a stiffness-based technique and/or able to

assess material properties

• Wave transmission modes may be sensitive to in-plane

displacements (interfacial changes)

• Requires high sensitivity (S/N) and possibly noise reduction

methods to recognize small changes in bonds

Enhanced Inspection Methods to

Characterize Bonded Joints:

Moving Beyond Flaw Detection to

Quantify Adhesive Strength

Enhanced Inspection Methods to

Characterize Bonded Joints:

Moving Beyond Flaw Detection to

Quantify Adhesive Strength


Adhesive vs. Cohesive FailureAdhesive vs. Cohesive Failure

Cohesive Fracture of Adhesive Film(Option 6 silane treatment)

Adhesive Failure at Interface(Option 4 no chemical treatment)


Angle Beam Ultrasonic Spectroscopy (ABUS)Angle Beam Ultrasonic Spectroscopy (ABUS)

• Compare received and transmitted waveforms in frequency domain; study

frequency/amplitude shifts & change in damping in FRF

• Oblique wave (broadband UT beam) introduces shear stress in the bond

line

• Difference between longitudinal wave and shear wave interrogation

-35

-30

-25

-20

-15

-10

-5

0

2 3 4 5 6 7 8

Bad bond

Good bond

Normal incidence reflection coefficient

Frequency (MHz)

Amplitude (dB)

-40

-30

-20

-10

0

0 2 4 6 8

Bad bond

Good bond

10Frequency (MHz)

Amplitude (dB)

Oblique incidence reflection coefficient

Frequency and Amplitude Shifts

Differentiate Bonds

Negligible Affects on Normal

Wave (?)


Nonlinear UltrasonicsNonlinear Ultrasonics

• Exploit contact nonlinearity in imperfect bonds

• Swept frequency or chaotic drive signals to generate unique

harmonics

• Potential for introducing damage because incident energy levels

must be high

Requires high fidelity to avoid missed/false calls -

signal changes may be small (low S/N)

Good BondWeak Bond


AANC Weak Bond Specimen ProductionAANC Weak Bond Specimen Production

•Screened mold release

•Diluted mold release

•Poor cure


TTU of Weak Bond Specimens Show TrendsTTU of Weak Bond Specimens Show Trends

1 2

Pristine -

Best

1 2

30% MR

Dilution70% MR

Dilution

1 2

66% MR

Screen

1 2

33% MR

Screen

1 2

100 MR

1 2

Room

Temp.

1 2


Conclusions on Weak Bond AssessmentsConclusions on Weak Bond Assessments

• Understanding physics of bond integrity is key – select

proper interrogation method (what do we exploit)

• One NDI method may not detect all sources of weak

bonds

• Several NDI techniques show promise

• Expected low signal-to-noise ratios provide the biggest

impediment; optimized excitation is important . . . .

• Ensure that inspection is truly nondestructive


QMI

Sonda-007CX

Airscan

T

R

Air Coupled UltrasonicsAir Coupled Ultrasonics

Backside 1

Backside 2

Backside 3

Backside 1

Backside 2

Backside 3

Pixel resolution of 0.1”


• Works by bathing the material in

microwave energy of an

essentially constant frequency

• The energy is reflected from each

interface of differing dielectric

constants within the specimen

• The reflected energy is

superimposed, creating a signal

that is acquired as an analog

voltage which is digitized

• This signal is sampled at

numerous discrete locations

across the sample to create a 2-D

image

Microwave Scanning (Evisive)Microwave Scanning (Evisive)

Automated scan table

Fiberglass Honeycomb Test Specimen


Microwave NDI Results for 3 Ply

Fiberglass Panel

Microwave NDI Results for 3 Ply

Fiberglass Panel

Some difficulty with

carbon skin inspections


• Sample surface is heated with a

pulse of electromagnetic

radiation from a flash lamp

• Heat from the surface diffuses

into the sample and is obstructed

by the presence of a subsurface

defect

• The accumulated heat energy at

the defect causes a transient

nonuniformity in the infrared

radiation

Flir A40 Uncooled IR Camera

Pulsed ThermographyPulsed Thermography


Pulsed Thermography Inspection

Results for 6 Ply Panels

Pulsed Thermography Inspection

Results for 6 Ply Panels

1

2

3

4

5 6

7

8

9

All flaws detected

Carbon Skin Fiberglass Skin


Disbond Detection & Growth Monitoring

with Piezoelectric Sensors



-0.3

-

0.

2

-

0.

1

0.

1

0.

2

0.

3

Voltage (V)

1000 2000 3000 400

0Time (S X 10-7)

Blue = Signal Through Good Bondline Region

Red = Signal Through Disbond Region

0

Piezoelectric Sensor Network

Sensor Data

Actuation Signal

Damage Detection

Damage Identification

Residual Strength Evaluation

Assessment for Continued Use

1 2 3 4

5 6 7 8

9 10 11 12

Sensor/Actuator

Structural Flaw






Pull tab flawAfter mold release flaw growth(50 KHz inspection)

1.00"5.00"

1.00"

1.00"

MOLD RELEASE (C

REATE

WEAK BOND AREA)

1.00"

6.00"

PULL TAB

(CREATE LAMINATE-TO-

STEEL DISBOND)

3.00"


CACRC Inspection Task Group Update and Overview on Advanced NDI Methods

for Composites

CACRC Inspection Task Group Update and Overview on Advanced NDI Methods

for Composites

Dennis RoachSandia National Labs

FAA Airworthiness Assurance Center(505)844-6078

[email protected]

All rights reserved. Disclosure of this document or any part thereof

to third parties or the use of any information therein is not permitted

except with prior written permission from the author or Sandia Labs.

Documents

Improving In-Service Inspection of Composite Structures · Improving In-Service Inspection of Composite Structures ... PE Phased Array UT UT Wheel Array ... (TWI -2) Laminography(Digiray)