Deep Penetration and Process Automation Application of Remote Field Eddy Current Technique in Aircraft NDI

Transcription

1 Deep Penetration and Process Automation Application of Remote Field Eddy Current Technique in Aircraft NDI Yushi Sun, Tianhe Ouyang, Harry Zhu, Xinle Yang, Weiqiang Wan & Changhong Sun IMTT 3141 W. Torreys Peak drive, Superior, CO Tel: , Kenneth LaCivita AFRL/RXSA, th Street, Room 122 WPAFB, OH Tel: , Richard Harrison 508 ACSS/GFEAF A-10 Structures Engineering Branch Hill AFB, UT Tel: , Cindy Littleton Hetzer 330 ACSG/GFEA Robins AFB, GA Tel: (478) , 1

2 Introduction Two of the top issues in aircraft NDI: 1. Detection of flaws without a need of structure removal. 2. Minimize human factor in aircraft inspection using automation of NDI process. 2

3 Introduction IMTT, supported by AFRL, Hill AFB and Robins AFB, developed novel techniques in automated NDI for deeply hidden flaw detection including: Detection of crack/corrosion in multiple layer aluminum and titanium aircraft structures without structure disassembly or fastener removal; Detection of crack/corrosion through thick composite layer without structure disassembly; Automated system for detection of crack through repaired bushings without removal of bushing. 3

4 Least Preconditions for Techniques Enabling Flaw Detection without Structure Removal 1. Penetrating through whole thickness of structure; 2. Penetrating through interface gaps between structure layers; 3. Inspection on only one side of structure. Addition to the above there should be reliable algorithm to differentiate flaw from aircraft structure variations 4

5 Technique Capability Comparison Capabilities Techniques Deep penetration EC - UT X Ray RFEC Thru interface gaps - Access one side only - RFEC is the only choice 5

6 RFEC for Tube Applications Two coupling paths 1) direct coupling path which decays faster 2) Indirect coupling path which decays slower Indirect coupling Path Drive Coil Direct coupling path Indirect coupling Path Pickup Coil Since the directly coupled field decays at a faster rate, coil placement can be optimized to sense only the indirect coupling signal or remote field signal. Defects on tube wall can be detected by Pickup Coil away from Excitation Coil 6

7 RFEC for General Applications To have the RFEC phenomenon to occur in objects of other geometries Drive Unit Direct Coupling Path Pickup Unit Indirect Coupling Path The probe blocks the direct coupling path. The energy released from the drive unit is forced to go along the indirect coupling path. Therefore, the entire signal received by the pickup unit has passed the wall twice and carries the whole information about the wall condition. 7

8 Super Sensitive Eddy Current Instrument SSEC II Modification of conventional EC instrument; capable of working with General purpose RFEC probes as well as conventional EC probes Higher sensitivity and larger gain to work with the extremely weak signal from an RFEC probe Fully computerized system capable of on the spot automatic control, signal processing and pattern recognition Light, small and portable 8

9 Instrument for field applications - SSEC III A Prototype 9

10 Corrosion detection 10

11 Part I Deeply hidden corrosion detection Topic 1 Deeply hidden corrosion detection using a sliding probe 5 Layer 2024 T3 Aluminum Specimen Total Thickness = Corrosion on Bottom of 5 th Layer Location = Footprint: 0.85 x 2.15 Rf4 V3A Location =

12 Part I Deeply hidden corrosion detection Topic 1 - Test Result 5 th Layer Bottom Side Corrosion Total Thickness = 0.643, Location =

13 Topic 2 Backside corrosion pitting detection using sliding probe thick aluminum plate 6 Corroded backside 24 13

14 Topic 3.1 Detection of 2 nd layer corrosion close to steel rivets using a sliding probe Specimen of 2-layer structure 2 ( ) corrosion 1 st layer aluminum Scan image Image distortion due to corrosion 6 steel fasteners Corrosion locations Scan area 2 nd layer aluminum 3 normal fasteners 14

15 Topic 3.2 Detection of 2 nd layer corrosion close to steel rivets using a rotary probe Probe head Three components for a manual rotary probe Motorized rotary probe Connector s Probe carriage Probe carriage Rotational guide Centering lens Rotation guide with suction base 15

16 Why rotary probe to minimize noise from fastener Drive coil Drive coil Sensor Sensor Fastener Fastener Probe 1 Constant signal unless there is a crack Fastener- head Excitation Coil Fastener- head Excitation Coil Diff Sensors Diff Sensors Probe 2 No signal unless there is a crack 16

17 Topic 3.2 Detection of 2 nd layer corrosion close to steel rivets using a rotary probe Impedance Plane Impedance Plane Impedance Plane Reduced signal value Signal distortion No-corrosion around Uniform corrosion around Local corrosion near-by Real [mv] Real [mv] Real [mv] Real [mv] 17

18 Topic 4 Corrosion detection thru thick composite layer A: Test setup Probe graphite epoxy composite thick aluminum corrosion aluminum B: Test results Impedance Plane Real Real Imaginary Imaginary Sampling points 18

19 Crack detection 19

20 Topic 4 Crack detection where no structure variation using a sliding probe 815.2mv 583.8mv 546.0mv 452.4mv deep deep deep deep Total thickness = wide Saw cut 20

21 Topic 5 Detection of cracks in steel fastener holes and close to 2 nd layer edge using a rotary probe Simulating a two-layer aircraft structure 2 nd layer edge 2 nd layer corner cracks First layer: thick aluminum 0.75 A AB B BC C CD D D0 2 nd layer: thick aluminum 21

22 Topic 5 Detection of cracks in steel fastener holes and close to 2 nd layer edge using a rotary probe Shape factor of impedance plane Test results No crack holes Cracked holes Corner EDM notches are detected 22

23 Topic 6 Detection of Ti layer cracks thru thick graphite epoxy composite layer using a rotary probe Angle = 1.13 Angle = No EDM No EDM corner EDM 23

24 Topic 7 Automated system for thru bushing inspection 24

25 Real Aircraft Sample Aircraft Wing Attach Fitting section with bushed holes containing cracks at interface x into bore at interface x into bore Two φ0.532 holes with Inconel bushings installed (yellow arrows/red outlined holes). Hole #3, large crack, x Hole #4, small crack, x Cracks at wing skin layer (red layer) 25

26 Sketch of the structure Steel aluminum Steel aluminum aluminum Crack aluminum Inconel 718 Bushing 26

27 Thru bushing inspection scanner Laptop SSEC II Instrument Specimen Complete system 27

28 System Capability 1. Bushing thickness: from to Crack/EDM size: from to thru EDM notch 3. Single and multiple cracks 4. Complete automation of inspection procedure, no human involvement a. Automated scan area location b. Automated bushing thickness measurement and download system settings c. Automated C-scan and image display d. Automated signal processing and crack identification 28

29 Typical results of crack detection Inconel 718 bushing, thickness = Bushing ID = 17/32 1,088mV 460mV Real Aircraft Sample crack # crack Real Aircraft Sample crack # crack No crack hole 29

30 SUMMARY 1. Two issues of concern in aircraft NDI: nodisassembly of airplane and automation of NDI process; 2. RFEC is one of the NDI technique having potential in aircraft NDI without need for aircraft disassembly; 3. Seven typical topics/examples have been introduced in the presentation showing the outstanding capabilities of RFE technique in aircraft corrosion detection, crack detection and NDI automation. 30