Stress Corrosion Cracking on the AP-3C OrionMr Trent Simcock & FLTLT Zachary Kerr

Surveillance and Response Systems Program Office

Aircraft Structural Integrity Symposium

Defence Plaza Melbourne, 18 Mar 19

Acknowledgement

• Airbus Australia Pacific Limited

• The University of Adelaide

Scope

• Background

• Phased Array Ultrasonics (PAUT)

• A09-752 PAUT Trial Aircraft

• Immediate Actions

• Remaining Fleet

• Wing Panel Riser Coupon Testing

Background• Early 2015 during an R3/SBI2 servicing cracking in the wing risers,

specifically at the H-clips was discovered.

• This resulted in a fleet wide inspection program.

• A09-759 was the fleet lead until its retirement in Dec 17.

• The fleet is currently managed via targeted inspections at 12 month intervals at known crack locations.

• Since initial inspection the remainder of the wings have not be reinspected.

Background – Fleet cracking RH Upper and Lower

Images Courtesy Airbus Australia Pacific

No. of cracks

1

2

3+

Images Courtesy Airbus Australia Pacific

Background – Fleet cracking LH Upper and Lower

No. of cracks

1

2

3+

What next?

So it’s 2018, the majority of the AP-3C fleet is to be retired from RAAF service.

Do you complete risk assessment for nine months of flying to be retained at the correct authority?

Would this be considered SFARP?

Phased Array Ultrasonics Trial

• A Phased Array Ultrasonics (PAUT) procedure was developed for use on the AP-3C upper and lower wing surfaces.

• Allowing for reduced inspection time, ability to inspect operating aircraft overnight, reduced WHS impact as no tank entry required.

• Detecting crack like indications, length (>.500 inch), no height from base of plank or depth of crack (all indications assumed through thickness).

9

Wing riser side view, three EDM notches and one H-clip with a crack extending between and outside both fastener holes

EDM Notches at different heights

Plank Skin

Base of Riser

H-Clip Fastener Holes

Crack Indication between H-Clip fastener holes (in-service crack)

Change in Riser Geometry at H-Clip

Images Courtesy 92WG NDI

Riser being InspectedWing Surface

H-Clip Holes Nil Damage

H-Clip Holes Nil Damage

Nil Data. Reason currently unknown

Base of Riser

Plank Skin

H-Clip Holes Nil Damage

Base of Riser, Change in geometry due to end of panel

Plank Skin

Phased Array Ultrasonics Trial

• PAUT procedure divides wing surfaces into 38 scan areas that cover 1-2 ribs by 2 panels

Can not inspect using PAUTNo H-clip

*Diagram developed and supplied by Airbus Australia Pacific Limited

Phased Array Ultrasonics Improvements

• Inability to determine height required tank entries to confirm in some instances.• This has since been developed by NDT&CT.

• Like-wise for through thickness cracking. This is significant when determining requirements for mid-riser cracking.• Currently under investigation by NDT&CT.

Wing riser side view, three EDM notches and one H-clip with a crack extending between and outside both fastener holes

Images Courtesy 92WG NDI

Height from panel skin towards riser free edge

Phased Array Ultrasonics height from panel skin

• Initial aircraft PAUT was trialled on was A09-752.

• First scan, 7 scan areas, 130 H-clip locations (out of 3170, 4%)• 15 new crack identified at 10 locations

• Second scan, 7 scan areas, 254 H-clips (8%)• Cracks identified in 5 new locations

• Third scan, 8 scan areas, 343 H-clips (11%)• Nil cracks over 0.500” detected

• A09-759 20% of H-clips inspected over a six month period.

PAUT Aircraft A09-752 (Initial Aircraft Trial)

So we have a new efficient inspection technique, NDT&CT are improving the precision of the technique and we are planning on flying two AP-3C aircraft until the introduction of Triton in

early 2023…

So are we SFARP?

• 100% H-clip inspection to occur across both aircraft by Dec 2019.• Combination of PAUT and ECSS (under nacelle regions)• Mid riser locations can be interrogated for cracking.

• A09-657• 100% inspection completed. 74 cracks over 50 locations• Carried out during a 2 week period (data interrogated after the fact) and

R2.

• A09-660• All PAUT inspections completed, awaiting R2 2019 for nacelle ECSS

inspections.• 50 cracks over 41 locations• Military Permit to fly – Cracking was discovered between H-clips which

was confirmed through thickness.• Further analysis deemed this acceptable with more frequent inspections.

Current Fleet

A09-657 (Port Wing)

A09-657 (Starboard Wing)

A09-660 (Port Wing)

A09-660 (Starboard Wing)

So now, we know the fleet configuration, our FE modelling is telling us we are good to go, even with reduced inspection

periods, but there is still one more piece to the puzzle.

Wing Panel Coupon Testing

• SRSPO in conjunction with Airbus Australia Pacific and the University of Adelaide carried out wing panel coupon compression testing.

• A09-755 RH Upper wing surface was used.

• All coupons had ECSS carried out to determine the amount and type of damage.

Type of Panel Type of Cracking Number of Panels

Buckling H-Clip 3

Buckling Through Thickness 3

Buckling Random SCC 4

Buckling No Cracking (Clean) 3

Crippling (Length <310mm) No Cracking 3

Crippling (Length <310mm) Through Thickness (artificial*)

3

Crippling (Length <310mm) Random SCC 2

• Coupon type and selection was constrained by available material.* Artificial cracks were created via the use of a Fein saw

Wing Panel Coupon Testing

Wing Panel Coupon Testing

• Setup• Steel clamps utilising bolts to stabilise the coupons.

• Coupon loaded via displacement control .1mm per minute

• Strain gauges – free edge of risers and skin side at base of riser.

• Inconsistencies• Asymmetrical loading

• Different loading between coupons due to set up.

(FEA

/Te

st)

Coupon Number

Comparison of Peak Compression Load

Wing Panel Coupon Testing

• Most FEA/Test values within 10-15% of 1.00

• Average = 1.05 (typically FEA failing at just above the test sample)

• 80% of results are within ±15%

• 67% of results are within ±10%

Round 2:

• More coupon samples = increased confidence.

• Improved damage seeding = Electrical Discharge Machine Notching (DST Group).

• Refine/Play with the FEM boundary conditions.

Wing Panel Coupon Testing

Questions ?