NDE of Kissing Bonds Using Acoustography

Transcription

1 NDE of Kissing Bonds Using Acoustography Presented by: 1 Dr. Anish Poudel, 1 Dr. Tsuchin P. Chu, 2 Mr. Keven Mitchell, 3 Dr. Jaswinder S. Sandhu 1 Department of Mechanical Engineering and Energy Processes 2 Department of Aviation Technologies Southern Illinois University, Carbondale, IL Santec Systems, Inc Malmo Drive, Arlington Heights, IL

2 Presentation Outline Background Composites Adhesive Bonding Weak/Kissing Bonds Rationale for Research Acoustography NDE Material Description & Fabrication TTU Acoustography Lab Test Setup Experimental Results TTU Acoustography Lap Shear Tests Correlation of Test Results SEM Analysis Conclusions Acknowledgements Questions Section of Boeing 787 fuselage TTU Acoustography

3 Background Demands for composites reached $21.2 billion with U.S. market about $8.2 billion in Aircraft/ aerospace composite market is estimated to be worth US $4.1 billion by US Composite Materials Market Forecast F-35 Lightening II 42% composites V-22 Osprey 43% composites Commercial Airliners Boeing 787 and Airbus A350 50% composites

4 Adhesive Bonding Modern aircraft structures has component pieces which have to be joined together. Composite hat stiffener Section of Boeing 787 fuselage Image Source: The Boeing Company Composite hat stiffener bonded to fuselage

5 Adhesive Bonding σ v Offer an attractive package for efficient structural designs. Key Advantages: Uniform stress distribution Lighter weight Higher fatigue resistance Mechanical fastener Overlap Region Corrosion resistance Cost effective σ v Stress distribution in bonded single lap shear joint Adhesive

6 Weak/Kissing Bonds Weak/kissing bond exhibits a very lower level of adhesion. Kissing bonds potentially occur during manufacturing or repairs due to : Contamination Incorrect surface preparation Basic bonding requirements Improper curing Residual stress Moisture ingress and corrosion Common defects in adhesive joints

7 NDE of Weak/Kissing Bonds Current state-of-art bondline quality inspection in aerospace industry uses following NDE methods: Ultrasonics - Compression-wave - Shear-wave - Laser based Ultrasonic System Infrared Thermography (IRT) - Sonic IRT - Pulse-Phased IRT IRT System Laser Shearography Neutron Radiography Holographic Interferometry Laser Bond System Laser Shearography Olympus Masterbond

8 Literature Reviews - Ultrasonics Kundu et al. (1998) Chambers et al. (1999) Heslehurst et al. (1999) Bossi et al. (2002) Brotherhood et al. (2003) Applied lamb wave approach on the detectability of kissing bonds. Applied swept-frequency ultrasonic spectroscopy approach to evaluate the bond quality in the nozzle of the Fastrac motor. Demonstrated holographic interferometry was successful in identifying regions of the weakened bond lines. Applied shock wave loads via laser to measure bonded joint strength. Studied effect of compressive loading on the ultrasonic detectability of kissing bonds.

9 Literature Reviews Other NDE Methods Michaloudaki et al. (2005) Yan et al. (2010) Tsoi et al. (2011) Waugh et al. (2011) Guo et al. (2012) Applied neutron radiography technique to evaluate defects in bond line and correlate the image results with bond strength. Applied non-linear ultrasonics approach to cause local mechanical deformation in the adhesive bonds. Used sonic IR technique for the inspection of F-11C lower wing skin samples with disbond defects. Applied pulse-phased IR technique to the surface of an adhesively bonded sandwich structure specimen. Applied laser shearography techniques for the assessment of kissing bonds in sandwich structures.

10 Rationale for Research Existing NDE methods have very limited capability that can identify and determine the strength of the bond or could produce a robust correlation between NDE data and bond shear strength. Demand for faster, accurate, easy-to-implement, and efficient NDE methods. Develop a novel Acoustography ultrasonic imaging and digital image correlation (DIC) techniques to meet the existing need.

11 Acoustography NDE Basic Concept Uses a Super High Resolution Large Area Ultrasound Detector X-ray Technique (AO Sensor) For Instant, Full-Field X-Ray like Ultrasound Imaging Acoustography Technique Poudel, A., et al., 2015 "Comparison and Analysis of Acoustography with Other NDE Techniques for Foreign Object Inclusion Detection in Graphite Epoxy Composites," Composites: Part B.

12 Basic Principle AO Sensor Based on the birefringent properties of LC materials contained in the sensor. No Ultrasound For LC layer, optical behavior (brightness change, T) is given by: T = sin 2 2πd λ. n n. sin 2 θ I Ultrasound d = LC layer thickness λ = wavelength of the light n = refractive index of LC molecule along the optic axis (n) n = refractive index of LC molecule perpendicular to optic axis (n) θ I = ultrasonically-induced tilt angle of the LC molecules which is a function of the ultrasonic intensity I. Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. AO Sensor working principle

13 Basic Image Formation Principle Polarized light source illuminates the AO sensor. Video camera with polarizer is employed to observe the image produced in the AO sensor. Frame grabber used to digitize the image for computer storage and further image processing. Image formation schematic

14 Lateral and Geometric Resolution Fresnel or Near Field Diffraction Length R=D 2 /λ D= Target (Defect) Diameter λ = wavelength in medium Beam Divergence Angle Sin( /2) ~ λ /D Defect Shape recognizable when L<R Defect Shape deteriorates gradually when L>R where, L = Defect-to-AO sensor distance Sandhu, J.S., et al., 2013 Evaluating Acoustography for Through-Transmisison Ultrasonic Inspection of Composites, Proceedings of 2013 ASNT fall conference, Las Vegas, NV.

15 Carbon/Epoxy Panels Newport NB-321 3K70P plain weave carbon fabric prepreg. 4-ply layup with orientation [0 /-45 /+45 /90 ]. Pressure molding technique used for curing. A typical cure cycle Polyester peel-ply fabric was used for creating clean surface for the bonding. Cured surface Peel-ply removed surface Peel-ply Cured panel with peel-ply SEM Micrograph for CFRP substrate after polyester peel ply removal

16 2024-T3 Aluminum Surface prepared by sandblasting followed by chromic acid etching developed by Forest Products Laboratory (FPL). Al panels were etched in the chromic acid bath. 25 minutes at C ( F). Laboratory chromic acid etching setup SEM Micrograph for Al substrate before pretreatment

17 2024-T3 Aluminum Surface prepared by sandblasting followed by chromic acid etching developed by FPL. Al panels were etched in the chromic acid bath. 25 minutes at C ( F). Isometric drawing of oxide structure SEM Micrograph for Al substrate after pretreatment Source: Courtesy of Martin Marietta Laboratories

18 Lap Shear Panels Fabrication Track 1 - Lap Shear Panels With Contaminants Three different contaminants used: Silicone lubricant Aircraft hydraulic fluid Poly-vinyl alcohol (PVA) Track 2 - Lap Shear Panels With Varying Resin-to-Hardener (A/B) Ratios Manufacture recommended A/B = 100/27 (standard). Variation of A/B: 100/15, and 100/10. Baseline samples were also prepared Kissing bond defect map Schematic showing 50% contaminations applied on CFRP substrate Contamination 0.5

19 Bonding Process Contaminants Contaminant introduced in clean CFRP bonding surface Bonding process/ schematic of construction jig and layup

20 Lap Shear Test Coupons 1 inch x 7 inch lap shear test coupons were cut from the 7 inch x 9 inch panels. ASTM D5868 was followed to prepare test coupons for lap shear testing. Loading rate: 2 mm/min. ASTM D5868 lap shear coupon schematic

21 Laboratory TTU Acoustography Setup Sound source used: 3 inch x 3 inch Piezo-electric plate with a center frequency of 3.8 MHz. AO sensor used had an operating frequency of 3.8 MHz to match that of the sound source. Immersion Tank Test Specimen Bondline Sound Source Workstation & PC Optics & Electronics AO Sensor Specimen Holder Laboratory test setup of TTU Acoustography technique

22 Grayscale histogram distributions TTU Acoustography Results-Track 1 Baseline Silicone Hydraulic Oil PVA Acoustography TTU results (0-12 db)

23 Load (N) Load (N) Load (N) Load (N) Lap Shear Test Results-Track Baseline (No Contamination) % Silicone Contamination μ σ 3110 N 71 N B-1 B-2 B μ σ 2359 N 111 N K-1 K-2 K Extension (mm) % Hydraulic Oil Contamination Extension (mm) % PVA Contamination μ σ 1555 N 139 N μ σ 1984 N 131 N H-1 H-2 H P-1 P-2 P Extension (mm) Extension (mm)

24 Lap Shear Strength (Pa) Lap Shear Strength-Track 1 6.0E+06 Average Shear Strength For Single Lap Shear CFRP-Al Joints 5.0E E E E E E+00 Baseline 50% Silicone 50% Hydraulic Fluid 50% PVA Si contaminated sample failed at relatively larger load compared to PVA and H-oil. This can be attributed to strong chemical reaction between epoxy and Si providing structural strength in expense of chemical energy. Interfacial failure was dominant failure mode in all specimens.

25 Test Results Correlation-Track 1 Surface contamination type loss (db) Absorbtion coefficient (db/mm) Average Bond Shear Strength (Mpa) Relative Bond Shear Strength Baseline % 50% Silicone % 50% Hydraulic Oil % 50% PVA % Region with contamination produces significant differential attenuation as opposed to the region without any contamination. Transmission loss and absorption coefficient values increased in the region of contamination with the decrease in bond shear strength.

26 TTU Acoustography Results- Track 2 Lap Shear Panels (Varying A/B Ratios) Histograms for the ROIs 100/27 100/15 TTU Acoustography results. Yellow rectangle are the region of interests (ROIs). 100/10

27 Load (N) Load (N) Load (N) Lap Shear Test Results-Track Sample 1 Sample 2 A/B ratio = 100/ Sample 1 Sample 2 Sample 3 A/B ratio = 100/15 μ σ 4059 N 257 N 4000 Sample μ σ 5484 N 221 N Displacement (mm) Displacement (mm) A/B ratio = 100/10 Load carry ability of the lap shear joint decreases with the decreasing amount of the hardener Sample 1 Sample 2 Sample 3 μ σ 1868 N 139 N Displacement (mm)

28 Average Lap Shear Strength Lap Shear Strength-Track 2 Average Lap Shear Strength For CFRP-Al Joints with Varying A/B Ratios 1.00E E E E E E E E E E E /27 100/15 100/10 Resin/Hardener Ratio (A/B) Bond shear strength decreases with the decreasing amounts of hardener.

29 Test Results Correlation-Track 2 Samples ID loss (db) Absorption coefficient (db/mm) Average Shear/Failure Strength (MPa) Relative Bond Strength 100/ % 100/ % 100/ % Ultrasonic attenuation increases with the decreasing amounts of hardener.

30 Failed Substrates-Track 1 Baseline Silicone Contamination Hydraulic Oil Contamination PVA Contamination Interfacial failure was a dominant mode in all cases.

31 Scanning Electron Microscopy Critical to understand Interaction of contaminants with the substrates and adhesives Energy Dispersive X-ray Spectroscopy (EDX) and elemental distribution were also carried out. Secondary electron imaging mode was used at low vacuum (~ 200 Pa). SEM at SIU Image Center No coating was used when analyzing the chemical composition. Inside view of the SEM

32 Elemental Weight % Elemental Weight % Elemental Weight % Elemental Weight % SEM EDX Results- Adhesive Baseline Silicone Contamination C O Al Si 0 C O Al Si Top Middle Bottom Top Middle Bottom Hydraulic Oil Contamination PVA Contamination C O Al Si 0 C O Al Si Top Middle Bottom Top Middle Bottom

33 SEM Results- Failed Substrate: Baseline Top Middle Bottom SEM micrograph Energy-dispersive X-ray spectroscopy (EDX)

34 SEM Results- Failed Substrate: Si Contamination Top Middle Bottom SEM micrograph Energy-dispersive X-ray spectroscopy (EDX)

35 SEM Results- Failed Substrate: H-oil Contamination Top Middle Bottom SEM micrograph Energy-dispersive X-ray spectroscopy (EDX)

36 SEM Results- Failed Substrate: PVA Contamination Top Middle Bottom SEM micrograph Energy-dispersive X-ray spectroscopy (EDX)

37 Conclusions TTU Acoustography showed promising results on the detection of interfacial bondline defects. Adhesive bondline becomes more attenuative to ultrasonic waves as it gets weaker. Ultrasonic transmission loss and absorption coefficient values increased in the region of contamination for the contaminated panels. Finally, strong correlation were established between the lap shear test results, and Acoustography results. Contaminants migrated during the curing of the adhesive from CFRP substrate which caused a decrease of bond shear strength

38 Acknowledgements Navy STTR Phase-I grant # N P-1214 IMEL Colleagues Mr. Ryan Spencer Mr. Shashi Shrestha Dr. Kanchan Mondal, MEEP, SIU, Carbondale, IL. Department of Civil Engineering, SIU, Carbondale, IL. College of Engineering, SIU, Carbondale, IL.

39 Questions/ Concerns? Thank you for your Attention!

40 Questions? Anish Poudel Department of Mechanical Engineering & Energy Processes Southern Illinois University 1230 Lincoln Dr., MC 6603, Carbondale, IL Ph ; Fax