SHIP STRUCTURE COMMITTEE 2012

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NTIS # PB2012-SSC-463INSPECTION TECHNQIUES FORMARINE COMPOSITECONSTRUCTION AND NDEThis document has been approvedFor public release and sale; itsDistribution is unlimitedSHIP STRUCTURE COMMITTEE2012

Ship Structure CommitteeRADM P.F. ZukunftU. S. Coast Guard Assistant Commandant,Assistant Commandant for Marine Safety, Securityand StewardshipCo-Chair, Ship Structure CommitteeRDML Thomas EcclesChief Engineer and Deputy CommanderFor Naval Systems Engineering (SEA05)Co-Chair, Ship Structure CommitteeMr. H. Paul CojeenSociety of Naval Architects and Marine EngineersDr. Roger BasuSenior Vice PresidentAmerican Bureau of ShippingMr. Christopher McMahonDirector, Office of Ship ConstructionMaritime AdministrationMr. Victor Santos PedroDirector Design, Equipment and Boating Safety,Marine Safety,Transport CanadaMr. Kevin BaetsenDirector of EngineeringMilitary Sealift CommandDr. Neil PeggGroup Leader - Structural MechanicsDefence Research & Development Canada - AtlanticMr. Jeffrey Lantz,Commercial Regulations and Standards for theAssistant Commandant for Marine Safety, Securityand StewardshipMr. Jeffery OrnerDeputy Assistant Commandant for Engineering andLogisticsMr. Edward GodfreyDirector, Structural Integrity and Performance DivisionDr. John PazikDirector, Ship Systems and Engineering ResearchDivisionSHIP STRUCTURE SUB-COMMITTEEAMERICAN BUREAU OF SHIPPING (ABS)Mr. Craig BoneMr. Phil RynnMr. Tom IngramDEFENCE RESEARCH & DEVELOPMENT CANADAATLANTICDr. David StredulinskyMr. John PorterMARITIME ADMINISTRATION (MARAD)Mr. Chao LinMr. Richard SonnenscheinMILITARY SEALIFT COMMAND (MSC)Mr. Michael W. ToumaMr. Jitesh KeraiNAVY/ONR / NAVSEA/ NSWCCDMr. David Qualley / Dr. Paul HessMr. Erik Rasmussen / Dr. Roshdy BarsoumMr. Nat Nappi, Jr.Mr. Malcolm WitfordTRANSPORT CANADANatasa KozarskiLuc TremblayUNITED STATES COAST GUARDSOCIETY OF NAVAL ARCHITECTS AND MARINEENGINEERS (SNAME)Mr. Rick AshcroftMr. Dave HelgersonMr. Alex LandsburgMr. Paul H. MillerCAPT John NadeauCAPT Paul RodenMr. Jaideep SirkarMr. Chris Cleary

CONVERSION FACTORS(Approximate conversions to metric measures)To convert fromLENGTHinchesinchesfeetVOLUMEcubic feetcubic inchesSECTION MODULUSinches2 feet2inches2 feet2inches4MOMENT OF INERTIAinches2 feet2inches2 feet2inches4FORCE OR MASSlong tonslong tonspoundspoundspoundsPRESSURE OR STRESSpounds/inch2kilo pounds/inch2BENDING OR TORQUEfoot tonsfoot poundsfoot poundsENERGYfoot poundsSTRESS INTENSITYkilo pound/inch2 inch½(ksi in)J-INTEGRALkilo pound/inchkilo videmultiply bydivide by39.370125.40003.2808cubic meterscubic metersdivide bydivide by35.314961,024centimeters2 meters2centimeters3centimeters3multiply bymultiply bymultiply by1.9665196.644816.3871centimeters2 meterscentimeters4centimeters4divide bymultiply bymultiply Newtonsmultiply bymultiply bydivide bydivide bymultiply by1.01601016.0472204.622.20464.4482Newtons/meter2 (Pascals)mega Newtons/meter2(mega Pascals)multiply bymultiply by6894.7576.8947meter tonskilogram metersNewton metersdivide bydivide bymultiply by3.22917.232851.35582Joulesmultiply by1.355826mega Newton MNm3/2multiply by1.0998Joules/mm2kilo Joules/m2multiply bymultiply by0.1753175.3

Marine Composites NDESSC-463Table of Contents1. Introduction.11.1 Executive Summary .11.2 Background .21.3 Acknowledgements.32. Defects .42.1 Bonded Joint Failure .42.2 Air Bubbles .62.3 Blisters .72.4 Core Crushing .82.5 Core Shear Failure .102.6 Crazing.102.7 Delaminations .112.8 Fiber Failure.132.9 Kissing Bond.142.10 Impact Damage .152.11 Matrix Cracking .182.12 Moisture Ingress.192.13 Pit (or pinhole) .202.14 Ply (or Fiber) Waviness .202.15 Porosity .212.16 Resin Rich Area .212.17 Resin Starved Area .212.18 Skin-to-Core Disbond .222.19 Surface Cracking.242.20 Thermal (and Lightning) Damage .252.21 Voids .263. NDE Techniques.283.1 Visual Inspection .283.2 Tap Testing .293.3 Ultrasonic Inspection .313.4 X-Radiography (X-Ray) .363.5 Eddy Current.363.6 Thermography.373.7 Moisture Meters .393.8 Bond Testers .393.9 Laser Shearography .393.10 Electron Probe Imaging .413.11 Modal Methods .423.12 SIDER .443.13 Acoustic Emission .454. Aerospace Damage and Repair Inspection Procedures .465. Wind Turbine Blades .575.1 Blade Inspection Program.605.2 Blade Flaw Characterization.616. Test Panel Program .636.1 Previous Composite Laminate Impact Test Programs.63Eric Greene Associates, Inc.v

Marine Composites NDESSC-463Table of Contents6.2 Project Test Panels.676.3 Induced Impact Damage .787. Test Panel NDE.817.1 Laser Shearography .817.2 Ultrasonic Inspection .857.3 Infrared Thermography.877.4 Digital Tap Hammer .908. Case Studies .928.1 Laser Shearography .928.1.1 RNLI Lifeboats .928.1.2 Damaged Yacht Hull.948.2 Infrared Thermography.948.2.1 Void Detection .958.2.2 Extent of Damage .968.2.3 Water Ingress .978.3 Ultrasonics .989. Summary .1019.1 Summary of NDE Techniques Examined.1029.2 Flaw Detection in Marine Composites .10310. Conclusion .10511. Recommendations for Future Research .10611.1 Develop Standardized Structural Details .10611.2 Develop Standardized Inspection and Repair Procedures .10711.3 Reduce the Cost of Laser Shearography NDE Equipment .10711.4 Develop a Method to Electronically Code the Location of NDE Equipment.107A-1. Appendix A – Defect Thresholds .108A-2. Appendix B – Effectiveness Summaries .111Glossary .116Text References .125Eric Greene Associates, Inc.vi

Marine Composites NDESSC-463Table of ContentsFiguresFigure 1. Bonded joint failure modes .4Figure 2. Cohesive (left) and Adhesive (right) bond failure examples.4Figure 3. Mixed-mode bond failure (light areas) and adhesion failure .5Figure 4. Examples of air bubbles in composite laminates .7Figure 5. Illustration of blisters in boat hulls.8Figure 6. Illustrations of core crushing .8Figure 7. Photographs showing core crushing in Nomex .9Figure 8. Schematic, FE-model and photograph of indentation damage.9Figure 9. Fatigue fracture of PMI 51 S foam core.10Figure 10. Examples of fiberglass crazing in gel coat finishes.10Figure 11. Examples of severe delamination resulting from manufacturing defects .11Figure 12. SEM micrographs of delaminated specimens after interlaminar shear .11Figure 13. Micrograph and X-ray image of an edge delamination.12Figure 14. Delamination of tabbed joint .12Figure 15. Kink band formation with composite laminates are under compression .13Figure 16. Micrograph of fiber fracture and fiber pullout .13Figure 17. Various types of “kissing” bonds .14Figure 18. Mode 1 frequency variation for bonded and disbonded conditions .14Figure 19. The influence of “peel ply” on “kissing” bond formation.14Figure 20. Impact damage types .15Figure 21. Impact damage schematic.15Figure 22. X-ray image of impact delaminations within a CFRP panel.16Figure 23. Photograph of delaminations on Nomex sandwich construction .16Figure 24. Damage types occurring from blunt and sharp object impact.17Figure 25. Foreign object impact damage in honeycomb-cored sandwich laminates .17Figure 26. Sandwich laminate impact damage .18Figure 27. Schematic representation of cracks in laminates.18Figure 28. Micrographs of matrix micro-cracking .19Figure 29. Schematic representation of moisture ingress in sandwich laminates.19Figure 30. Image of pits or pinholes .20Figure 31. Ply waviness morphologies made visible by laminate edge photographs.20Figure 32. FE model geometry, representing one wavy 0º ply.20Figure 33. Composite sample close-up of apex showing extreme fiber-waviness .20Figure 34. Schematic of laminate porosity .21Figure 35. Resin starved areas and micrograph of resin rich areas .22Figure 36. Voids and resin-rich areas shown with backscattered electron imaging.22Figure 37. Schematic of skin-to-core disbond .23Figure 38. Photograph of skin to-core de-bond in a GRP skin, PU foam sandwich .23Figure 39. Crack length measurements showing crack path in PVC foam .23Figure 40. Schematic of surface cracks .24Figure 41. Micrographs of resin burn-off and delaminations from lightning strike.25Figure 42. Lightning damage to wind turbine blades .26Figure 43. Path of lightning strike on sailing yacht with carbon fiber mast.26Figure 44. Micrographs of voids in pre-preg and filament wound materials .27Eric Greene Associates, Inc.vii

Marine Composites NDESSC-463Table of ContentsFigure 45. Approximate frequency spectrum for techniques used in NDE.28Figure 46. Picture of a military specification tap hammer.29Figure 47. PoD for Visual and Tap Hammer Inspection Methods .30Figure 48. Typical ultrasonic phased array probe assemblies .32Figure 49. Single-element contact ultrasonic transducer and A-scan image .32Figure 50. Ultrasonic transducer scan movement and linear scan B-scan image.33Figure 51. EPOCH 1000i ultrasonic and phased array flaw detector .34Figure 52. Logarithmic time evolution of surface temperature .38Figure 53. Shearography principal and portable shearography device.41Figure 54. Frequency response plot from vibrometer.43Figure 55. An instrumented hammer is used during SIDER examination .44Figure 56. Aerospace structural design load and damage considerations .46Figure 57. Schematic of a reference standard used for NDE of cored panels .47Figure 58. Reference standard used for NDE of solid laminates.48Figure 59. Probability of Detection (PoD) for composite sandwich panels .48Figure 60. Probability of Detection (PoD) for carbon fiber sandwich panel.49Figure 61. Comparison of advanced inspection techniques with conventional NDE.49Figure 62. Cumulative PoD of all conventional NDE devices .50Figure 63. Cumulative PoD for Woodpecker device.50Figure 64. Some NDE devices evaluated by the FAA.51Figure 65. Ultrasonic backwall echo reduction versus volume porosity .52Figure 66. Phased array inspection of stringer skin bonding.53Figure 67. Entrapped water in a honeycomb panel and a thermographic image.54Figure 68. Various NDE technologies evaluated by Airbus.55Figure 69. Effectiveness of NDE techniques for honeycomb structures by Airbus .56Figure 70. Wind turbine blade damage.58Figure 71. Wind turbine blade damage (continued) .59Figure 72. Blade damage formation and growth .59Figure 73. Photographs of wind blade damage.60Figure 74. Classification and quantification of blade defects.62Figure 75. Impact energies used for previous aerospace impact test studies.64Figure 76. Impact damage apparent only with NDE and core crushing process.64Figure 77. Void simulation cavity machining diagram for Pearson 4 test panel.68Figure 78. Void simulation cavity machining diagram for Pearson 5 test panel.68Figure 79. Void simulation cavity machining diagram for Pearson 6 test panel.69Figure 80. Void simulation cavity machining diagram for Pearson 7 test panel.69Figure 81. Description of panels USNA 1 and USNA 2 .70Figure 82. Description of panels USNA 3 and USNA 4 .71Figure 83. Description of panels USNA 5 and USNA 6 .71Figure 84. Description of panels USNA 7 and USNA 8 .72Figure 85. Description of panels USNA 9 and USNA 10 .72Figure 86. Layout of E-glass and carbon fiber test panels.74Figure 87. Test panel delamination arrangement.75Figure 88. Test panel water ingress arrangement .75Figure 89. Test panel shear defect arrangement .76Figure 90. Test panel construction.76Eric Greene Associates, Inc.viii

Marine Composites NDESSC-463Table of ContentsFigure 91. Test panel construction (continued) .77Figure 92. Test panels with 1-inch grid for damage location reference .77Figure 93. Rubber coated barbell is epoxied into PVC tube to form impactor .78Figure 94. Detail of impactor release mechanism .79Figure 95. Impact tester at the US Naval Academy Structures Laboratory.79Figure 96. Vacuum chamber and laser shearography camera .81Figure 97. Panel “Osprey 1” with simulated delaminations and shearograms .82Figure 98. Panel “Osprey 3” with simulated core shear and shearograms .82Figure 99. Panel “Osprey 4” with induced impact damage and shearograms .82Figure 100. Panel “Osprey 6” with simulated water ingress and shearograms .83Figure 101. Panel “Osprey 8” with induced impact damage and shearograms .83Figure 102. Panel “Pearson 4” with machined back-face cavities and shearograms.83Figure 103. Panel “Pearson 6” with machined back-face cavities and shearograms.84Figure 104. Panel “USNA 3” with induced impact damage and shearograms.84Figure 105. Panel “USNA 10” with induced impact damage and shearograms.84Figure 106. Acoustocam i600 used to inspect a project carbon fiber panel .85Figure 107. Impact energies and corresponding ultrasonic NDE data .86Figure 108. Delamination damage and corresponding ultrasonic NDE data.86Figure 109. Machined cavities and corresponding ultrasonic NDE data.86Figure 110. Mark Ashton is shown capturing and analyzing the IR image.87Figure 111. Panel “Osprey 6” with simulated water ingress and thermogram.88Figure 112. Panel “Pearson 6” with machined back-face cavities and thermogram .88Figure 113. Panel “USNA 3” with impact damage and thermogram .89Figure 114. Panel “USNA 6” with impact damage and thermogram .89Figure 115. Digital tap hammer being used to evaluate an Osprey E-glass panel.90Figure 116. Vacuum hood used to test flat panel portions of RNLI lifeboat hulls.92Figure 117. RNLI Severn class topside hull and shearography images .93Figure 118. RNLI Severn class detected hull defects over time.93Figure 119. Full extent of internal damage to hull sandwich construction.94Figure 120. Visible NDE looks defect free but thermal pattern shows anomaly .95Figure 121. Thermographic image of void in gel coat.95Figure 122. Red and white areas indicate anomalies in bondline or skin.96Figure 123. Infrared image above indicates good contact between skin and core .96Figure 124. IR image shows moisture ingress to keel box .97Figure 125. IR anomalies on hull bottom characteristic of moisture ingress .97Figure 126. The dark colored anomaly is characteristic of moisture.98Figure 127. The captured UT waveform of a carbon fiber mast .99Figure 128. UT shows the top reinforcement layer in this area is delaminated.100Eric Greene Associates, Inc.ix

Marine Composites NDESSC-463Table of ContentsTablesTable 1. Causes of cohesion failures.6Table 2. Effect of transducer frequency on UT Inspection of composites .35Table 3. Shearography stress method applicability .40Table 4. Laminates studied by Hildebrand .65Table 5. Impact energies studied by Hildebrand .65Table 6. Laminates studied by Marine Materials Laboratory.66Table 7. Impact Energies studied by Marine Materials Laboratory .66Table 8. Solid laminates built by Pearson Yachts.67Table 9. Fabricated test panels.73Table 10. Impact energies used to damage test panels .80Table 11. Effectiveness of digital tap hammer .91Table 12. Summary results from panel testing program.102Eric Greene Associates, Inc.x

Marine Composites NDESSC-463Introduction1. Executive SummaryThe goal of this project was to conduct an assessment of current Non-DestructiveEvaluation (NDE) methods for large, marine composite structures. The assessmentsurveyed the military, commercial and recreational industries. Informational sourcesincluded marine surveyors, NDE equipment manufacturers, shipbuilders, platformowners and academia.Concurrently, a separate assessment of flaw criticality was conducted to determine thelower limit size of as-built flaws or in-service damage that needs to be detected in orderto ensure structural integrity. The critical flaw size for a variety of defects formed thebasis for NDE detectablity thresholds.Test panels were assembled or fabricated with imbedded defects to determine the efficacyof various NDE methods. The panels had the following defects:Delamination or voids were simulated in solid laminates by machining 1-4 inchdiameter cavities from 20% to 80% of panel thickness. Delaminations weresimulated in sandwich laminates by placing peel-ply material in between thereinforcement plies. The defects ranged from 0.5 to 4.0 inches in diameter.Water Ingress was simulated by embedding pockets of water 1-4 inches indiameter into the core just below the top skin.Core Shear was simulated in sandwich panels by slitting the core prior tolamination and inserting peel ply into the slot during fabrication.Impact Damage was induced with impact energies between 25 and 250 footpounds using a drop weight impactor.The initial assessment of NDE technologies revealed laser shearography, thermography,ultrasonic testing and digital tap hammers to be the most promising for marine compositeinspection. These technologies were all evaluated during the project’s test program.Laser shearography proved to be the most effective NDE technique for discovering thewidest variety and smallest defects, perhaps because this is the only NDE method thatstresses the part during inspection. It is also the most recently developed technology, andthus the most expensive.Thermography worked very well to detect water ingress and irregularities in sandwichconstruction, especially with cores that have kerfs.Ultrasonic inspection worked well to document the location and depth of delaminationsbut small survey probes limit the effectiveness to instances where damage sites areknown or suspected.The digital tap hammer proved to be effective only for larger delamination sites.Eric Greene Associates, Inc.1

Marine Composites NDESSC-463Introduction1.2 BackgroundAn increasing number of marine structures are utilizing composite materials. Majorstructure and components can be built lighter and corrosion-resistant using composites.The US Navy’s DDG-1000 topside structure and LPD-17 advanced enclosed mast arebeing built with composites. Additionally, the offshore oil industry is starting to buildcomposite risers and habitability modules. Nondestructive Evaluation (NDE) techniquesdeveloped for composite aerospace structures are not viable for large marine structures.Therefore, a state-of-the-a

pounds/inch 2 Newtons/meter (Pascals) multiply by 6894.757 : kilo pounds/inch2 2mega Newtons/meter (mega Pascals) multiply by : 6.8947 BENDING OR TORQUE: foot tons : meter tons divide by : 3.2291 foot pounds : kilogram meters divide by : 7.23285 foot pounds : Newton meters multiply by :

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