f/a-18a/b inner wing step lap joint defect management · f/a-18a/b inner wing step lap joint defect...

DGTA-ADF DDAAFS ACPA

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F/A-18A/B Inner Wing Step Lap Joint Defect Management

2016 ASI Symposium

FLTLT Chris Kourloufas (DASA-ASI) and Mr Jason Wittkopp (QinetiQ)

Nov 2016

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Summary

Symposium Theme: Capability Through an Integrated ASIP

• Background

• Initial RAAF response

• PAUT technology fundamentals

• RAAF PAUT inspection

• NDT comments

• RAAF findings

• DST interpretation of results

• USN analysis of defects

• Notable worldwide findings

• Current management strategy

• Lessons learned for other platforms

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Background

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• 2002 – RCAF identify an issue that compromises the integrity of the Inner Wing Step Lap Joint (IWSLJ) of the F/A-18 A-D

– Fracture Critical Structure – Catastrophic consequence of failure

• 2010 USN begin finding this issue during High Flight Hour inspections

– Forensic teardown revealed trace elements pointing to contamination at time of manufacture.

– Exact root cause undetermined

• Result of contamination is disbonding between Titanium and film adhesive.

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Inner Wing Step Lap Joint Area

4

UP

OUTBD

Composite

Material

Titanium

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Recent DST Investigation of Original USN Wing

9 8 7 6 5 4 3 2

9 8 7 6

5 4 3 2

1

1

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Background cont.

• Extensive disbonding will lead to overall failure of the joint and load will likely be transferred to the substructure via the skin fasteners.

• Disbonds are susceptible to growth in-service.

– Growth rate is unpredictable (cannot directly associate to AFHRS, loading history or any other parameter).

– Techniques to characterise disbond growth do not exist

• Predicted USN fall out rate was ~1%. Actual fall out rate ~2%.

• USN remediation action was to inspect fleet and monitor.

– Inspection of Outer Mold Line (OML) only possible

– Conservative joint static analysis possible (A4EI)

• Wings with extensive damage are replaced (negative static MoS).

– No repair options

– Wing skin change uneconomical

• Build quality issues

• Rectifying other defects

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Initial RAAF Response

• Options to procure USN automated UT equipment explored (MAUS)

– Option not pursued

• NDT&CT engaged by TFSPO to develop an inspection procedure

– NDT&CT contract QinetiQ to develop PAUT inspection

– High degree of DST input to procedure development

• NUC raised to communicate risk for OAAR acceptance

– AVRM = LOW

• Catastrophic consequence, however, no aircraft losses due

to IWSLJ bond failure

• RAAF expecting to have similar defect rate as USN ~2%

– Timeline set to develop procedure and inspect fleet

• USN engaged to provide static analysis support

– Access to enveloping analysis

– Any ad-hoc cases

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PAUT Fundamentals and QinetiQ Procedure

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© Copyright QinetiQ Pty Ltd 20131

PHASED ARRAY ULTRASONIC INSPECTION of F/A-18 ClassicInner Wing Splice Lap Joint

Jason Wittkopp NDT L2

A presentation to: ASI

17 Nov 2016

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1. SINGLE CRYSTAL TRADITIONAL ULTRASONICS

Single-element (non-phased array) probes, known technically as monolithic probes,

emit a beam at a fixed angle (either 0, 45, 60, 70 degrees).

This includes Pulse Echo Amplitude (PEA).

To test or interrogate a large volume of material, a conventional probe must be

physically scanned (moved or turned) to sweep the beam through the area of interest.

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2. PHASED ARRY ULTRASONICS

Phased array ultrasonics(PAUT) is an advanced method of ultrasonic testing that has

applications in medical, industrial and aviation NDT.

• Common Aviation Applications – non-invasively examine and detect flaws induced in the

manufacturing process and in in-service components.

− Manufacturing defects – foreign materials, porosity, un-bonds (failure of the materials to

bond during manufacture), etc.

− In-service defects – Fatigue cracking, disbonding (loss of adhesive integrity during in-service

operations), delamination, impact damage, etc.

• Can be used to test solid materials (Aluminium), composite materials (CFRP), and structures

combining mixture of both (Lap Joints, etc.).

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The beam from a phased array probe can be focused and

swept electronically without moving the probe. The beam

is controllable because a phased array probe is made up

of multiple small elements, each of which can be pulsed

individually at a computer-calculated timing.

The term phased refers to the timing, and the term array

refers to the multiple elements.

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3. IWSLJ Description

The Inner Wing Splice Lap Joint runs from the Front Spar to the Trailing Edge Spar and

is approximately 9 inches wide.

The test area is approximately 65 inches long by 14 inches wide for a total of

3,672 square inches of test area per aircraft.

The test is to determine the bonding integrity of the carbon to the titanium.

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If using a single Element probe 0.5 inch diameter –

• 4 data collection points are needed per square inch for a total of 14,688 points per aircraft,

with no data saved for review or presentation

• Would take an estimated 2 days to test, interpret the signal, plot any defects, measure and

record results

• Can only be used to interrogate the Outer Mould Line

• Signal interpretation is very complex and subtle defects could be missed

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4. Using PAUT for the IWSLJ

Detect defects on the Outer and Inner Mould Line

Possible to scan an entire aircraft in around 4-6 hours

1,241,136 data points per aircraft or 84.5 times more data than conventional UT

This data is –

• Stored and able to be retrieved for direct comparison against future inspections

• Presented to the Technician in a display presentation which can be manipulated to present

the data in several different styles to assist in defect identification and location

• The data can be recalled and used for a direct comparison against future testing

Defects that can be detected include –

• Disbonds

• Un-bonds

• Inter-laminar cracking, delaminations

• Porosity, foreign materials

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Defect sizes that can be detected are identified as –

• Greater than 0.5 inch diameter Outer Mould line

• Greater than 0.75 inch diameter Inner Mould line

However, smaller defects can be detected and reporting requirements will dictate

whether these defects are reported. The raw data will remain on file, which can be

recalled and compared in the future for comparison review, if required.

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5. Closing

PAUT provides an inspection method that is far superior to conventional UT by –

• Being able to inspect the Outer and Inner Mould lines

• Reducing scanning time on the aircraft and reducing technician fatigue

• Providing data that can be recalled and compared against future inspections

• Provides the technician with more information to allow for more accurate defect

identification

This inspection is the first PAUT procedure released for the ADF. There were many issues that

needed addressing during this procedure development, and as the technicians and procedure

development personnel become more experienced, PAUT should become an accepted technique

to inspect the new materials coming into service and should also be considered if large area or

complex geometries are needed to be tested.

www.QinetiQ.com.au


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RAAF Findings

• Initial finding hit rate has been high - ~18% aircraft with indications

– NDT&CT second-level review of first 20 NDT reports

• Provide feedback to NDTTECHs

• Clarify any disputed findings

– DST PAUT SME engaged to review scans by exception

• Abnormal/suspect indications

• Scan raw data shared easily on Objective (GB)

• High indication rate likely not related to capability of PAUT vs. MAUS

Start of defect End of defect

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DST Interpretation of Defect Indications

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INDICATION 1 (STEP 9) INDICATION 2 (SURFACE OF SKIN ABOVE STEP 9) INDICATION 3 (STEP 3)

DEFECT

TYPE DEFECT LIKELIHOOD

JUSTIFICATION LIKELIHOOD

JUSTIFICATION LIKELIHOOD

JUSTIFICATION

Su

rface

Paint/upper-ply

damage 1. Rare No surface indications. 5. Almost Certain

Clear, superficial indication, uniformly

reducing ultrasound transmission.

Loop-shaped defect clearly visible on

B-scan at the top surface. Similar

indications appear in a number of other

locations on the wing, but presumably

not reported due to size being below

reportable defect size

1. Rare No surface indications.

Ad

hesive

Ti-adhesive disbond 1. Rare No disbond reflection. 1. Rare Indication is from surface. 3. Possible

A small additional echo occurring at the

adhesive-Ti step interface is indicative of a

possible Ti-adhesive disbond. Similar to

A21-008, in that it does not significantly

affect ultrasound transmission, and hence

would need to be a tightly compressed

disbond at this layer.

Cohesive disbond 1. Rare No disbond reflection. 1. Rare Indication is from surface. 3. Possible As the indication is within the adhesive

layer, it could possibly be caused by a

compressed adhesive disbond.

Adhesive-composite

disbond 1. Rare No disbond reflection. 1. Rare Indication is from surface. 2. Unlikely

A disbond in the adhesive to composite

layer is considered unlikely as the adhesive

is clearly visible, which, in the case of an

adhesive to composite disbond, would likely

be shadowed.

Foreign inclusion 3. Possible

No consistent disbond or additional ply

signal along the length of the

indication. However, consistent loss of

reflection amplitude, reminiscent of a

geometry change (sloping

ply/adhesive layer/bunched adhesive

scrim) scattering the beam, possibly

suggestive of a foreign inclusion.

1. Rare Indication is from surface. 3. Possible

The amplitude of the echo is reminiscent of

an additional ply or a well-bonded inclusion.

However, the geometry is non-uniform along

the indication length.

Film adhesive porosity 2. Unlikely

Considered unlikely that the signal is

indicative of film adhesive porosity,

however an evenly distributed layer of

micro-porosity could give rise to the

signal.

1. Rare Indication is from surface. 2. Unlikely The uniformity of the amplitude response of

the indication suggest it's unlikely to be a

layer of voiding in the adhesive.

Fluid ingress 1. Rare Would expect to see reflection from the

fluid layer in this case. 1. Rare Indication is from surface. 3. Possible

Plausible waveform response and geometry

for the presence of a fluid layer, with fluid

ingress possible through the fastener

locations on step 3.

Co

mp

osite

Composite porosity 1. Rare No indications in composite material. 1. Rare Indication is from surface. 1. Rare No indications in composite material.

Composite

delamination 1. Rare No indications in composite material. 1. Rare Indication is from surface. 1. Rare No indications in composite material.

Matrix cracking 1. Rare No indications in composite material. 1. Rare Indication is from surface. 1. Rare No indications in composite material.

Fluid ingress 1. Rare No indications in composite material. 1. Rare Indication is from surface. 1. Rare No indications in composite material.

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USN Analysis Support

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• USN engaged to analyse wings

by exception

– Only those that fall outside of the

enveloping analysis

– 1D Static using A4EI

methodology

– Highly conservative load case

used

– ETW conditions applied

– Both OML and IML considered

disbonded

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Other Notable Worldwide Findings

• Foreign fleet inspection status is reported during regular ASI and

F/A-18 program meetings.

– Defect rates similar to USN.

– Feedback on techniques and processes valuable to ASIP

• SAF delamination growth finding 2016:

– First confirmed growth of disbond in service (within 60 AFHRS)

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Current Management Strategy

• Quantify fleet condition ASAP

– Types of indications, size, locations, etc

• Monitor indications for defect growth

– Aircraft with indications and analysis showing positive MoS are placed on a 50AFHR SBI interval (in line with USN and SAF policy)

– Reinspect pristine aircraft at DM interval

• Replace wings where necessary

• Correlate PAUT signal to type of anomaly

– Better understand what is a disbond, porosity, foreign object, etc.

• Continue with research, however, not expected to have tools for ready implementation on the Classic Hornet.

– 3D LEFM FEA analysis to investigate growth behaviour

– Coupon testing program to validate FEA

– Forensic investigation of in-service assets

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Lessons for Other Platforms

• Design criteria – ‘no growth’ could not be relied upon.

• Very complicated problem - worldwide capabilities to understand

the issue do not come close to those available for of metallic fatigue

problems.

• Few SMEs in the world.

• Relationships between SPO, ASI, DST, QinetiQ as well as the

international community (especially USN, SAF) absolutely critical.

– Integrated ASIP is key to success

– “Dare to share”

• Long lead time to stand up bespoke NDI/Analysis capabilities.

– High level of technical risk in such pursuits

• Fatigue propagation models do not exist – no way of understanding

damage growth within composites/bonded joints.

– Neither specific nor general models available for certifying any

solution.

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QUESTIONS

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