Basic Ultrasound Physics - PowerPoint PPT Presentation

1
IntroductionE Mch 521, ACS 521Stress Waves in
Solid Media3 credit Graduate Course

• Penn State University
• Instructors
• Dr. Joseph L. Rose
• Dr. Cliff Lissenden
• Textbook
• Ultrasonic Guided Waves in Solid Media
• Joseph L. Rose Cambridge University Press
  2014

2
Preface

• Text Ultrasonic Waves in Solid Media, 1999
• Nondestructive Evaluation
• Structural Health Monitoring
• Growth of Guided Waves 1985 to 2014
• Publications to 2000 and beyond
• University involvement (2 to 40)
• Commercialization piping example
• ASNT working on inspection certification, a new
  method
• ASME, DOT code requirements/developments

3
Table of Contents

• Nomenclature
• Preface
• Acknowledgments
• 1. Introduction
• 1.1 Background
• 1.2 A Comparison of Bulk versus Guided Waves
• 1.3 What Is an Ultrasonic Guided Wave?
• 1.4 The Difference Between Structural Health
  Monitoring (SHM) and
  Nondestructive Testing (NDT)
• 1.5 Text Preview
• 1.6 Concluding Remarks
• 1.7 References

4
Table of Contents cont.

• 2. Dispersion Principles
• 2.1 Introduction
• 2.2 Waves in a Taut String
• 2.2.1 Governing Wave Equation
• 2.2.2 Solution by Separation of Variables
• 2.2.3 DAlemberts Solution
• 2.2.4 Initial Value Considerations
• 2.3 String on an Elastic Base
• 2.4 A Dispersive Wave Propagation Sample Problem
• 2.5 String on a Viscous Foundation
• 2.6 String on a Viscoelastic Foundation
• 2.7 Graphical Representations of a Dispersive
  System
• 2.8 Group Velocity Concepts
• 2.9 Exercises
• 2.10 References

5
Table of Contents cont.

• 3. Unbounded Isotropic and Anisotropic Media
• 3.1 Introduction
• 3.2 Isotropic Media
• 3.2.1 Equations of Motion
• 3.2.2 Dilatational and Distortional Waves
• 3.3 The Christoffel Equation for Anisotropic
  Media
• 3.3.1 Sample Problem
• 3.4 On Velocity, Wave, and Slowness Surfaces
• 3.5 Exercises
• 3.6 References

6
Table of Contents cont.

• 4. Reflection and Refraction
• 4.1 Introduction
• 4.2 Normal Beam Incidence Reflection Factor
• 4.3 Snells Law for Angle Beam Analysis
• 4.4 Critical Angles and Mode Conversion
• 4.5 Slowness Profiles for Refraction and
  Critical Angle Analysis
• 4.6 Exercises
• 4.7 References

7
Table of Contents cont.

• 5. Oblique Incidence
• 5.1 Introduction  
• 5.2 Reflection and Refraction Factors
• 5.2.1 Solid-Solid Boundary Conditions
• 5.2.2 Solid-Liquid Boundary Conditions
• 5.2.3 Liquid-Solid Boundary Conditions
• 5.3 Moving Forward
• 5.4 Exercises
• 5.5 References

8
Table of Contents cont.

• 6. Waves in Plates
• 6.1 Introduction
• 6.2 The Free Plate Problem
• 6.2.1 Solution by the Method of Potentials
• 6.2.2 The Partial Wave Technique
• 6.3 Numerical Solution of the Rayleigh-Lamb
  Frequency Equations
• 6.4 Group Velocity
• 6.5 Wave Structure Analysis
• 6.6 Compressional and Flexural Waves
• 6.7 Miscellaneous Topics
• 6.7.1 Lamb Waves with Dominant Longitudinal
  Displacements
• 6.7.2 Zeros and Poles for a Fluid-Coupled
  Elastic Layer
• 6.7.3 Mode Cutoff Frequency
• 6.8 Exercises
• 6.9 References

9
Table of Contents cont.

• 7. Surface and Subsurface Waves
• 7.1 Background
• 7.2 Surface Waves
• 7.3 Generation and Reception of Surface Waves
• 7.4 Subsurface Longitudinal Waves
• 7.5 Exercises
• 7.6 References

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Table of Contents cont.

• 8. Finite Element Method for Guided Wave
  Mechanics
• 8.1 Introduction
• 8.2 Overview of the Finite Element Method
• 8.2.1 Using the Finite Element Method to Solve
  a Problem
• 8.2.2 Quadratic Elements
• 8.2.3 Dynamic Problem
• 8.2.4 Error Control
• 8.3 FEM Applications for Guided Wave Analysis
• 8.3.1 2-D Surface Wave Generation in a Plate
• 8.3.2 Guided Wave Defect Detection in a
  Two-Inch Steel Tube
• 8.4 Summary
• 8.5 Exercises
• 8.6 References

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Table of Contents cont.

• 9. The Semi-Analytical Finite Element Method
• 9.1 Introduction
• 9.2 SAFE Formulation for Plate Structures
• 9.3 Orthogonality-Based Mode Sorting
• 9.4 Group Velocity Dispersion Curves
• 9.5 Guided Wave Energy
• 9.5.1 Poynting Vector
• 9.5.2 Energy Velocity
• 9.5.3 Skew Effects in Anisotropic Plates
• 9.6 Solution Convergence of the SAFE Method
• 9.7 Free Guided Waves in an Eight-Layer
  Quasi-Isotropic Plate
• 9.8 SAFE Formulation for Cylindrical Structures
• 9.9 Summary
• 9.10 Exercises
• 9.11 References

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Table of Contents cont.

• 10. Guided Waves in Hollow Cylinders
• 10.1 Introduction
• 10.2 Guided Waves Propagating in an Axial
  Direction
• 10.2.1 Analytic Calculation Approach
• 10.2.2 Excitation Conditions and Angular
  Profiles
• 10.2.3 Source Influence
• 10.3 Exercises
• 10.4 References

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Table of Contents cont.

• 11. Circumferential Guided Waves
• 11.1 Development of the Governing Wave Equations
  for Circumferential Waves
• 11.1.1 Circumferential Shear Horizontal Waves
  in a Single-Layer Annulus
• 11.1.2 Circumferential Lamb Type Waves in a
  Single-Layer Annulus
• 11.2 Extension to Multiple-Layer Annuli
• 11.3 Numerical Solution of the Governing Wave
  Equations for Circumferential Guided
  Waves
• 11.3.1 Numerical Results for CSH-Waves
• 11.3.2 Numerical Results for CLT-Waves
• 11.3.3 Computational Limitations of the
  Analytical Formulation
• 11.4 The Effects of Protective Coating on
  Circumferential Wave Propagation in Pipe
• 11.5 Exercises
• 11.6 References

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Table of Contents cont.

• 12. Guided Waves in Layered Structures
• 12.1 Introduction
• 12.2 Interface Waves
• 12.2.1 Waves at a Solid-Solid Interface
  Stoneley Wave
• 12.2.2 Waves at a Solid-Liquid Interface
  Scholte Wave
• 12.3 Waves in a Layer on a Half Space
• 12.3.1 Rayleigh-Lamb Type Waves
• 12.3.2 Love Waves
• 12.4 Waves in Multiple Layers
• 12.4.1 The Global Matrix Method
• 12.4.2 The Transfer Matrix Method
• 12.4.3 Examples
• 12.5 Fluid Couples Elastic Layers
• 12.5.1 Ultrasonic Wave Reflection and
  Transmission
• 12.5.2 Leaky Guided Wave Modes
• 12.5.3 Nonspecular Reflection and Transmission
• 12.6 Exercises
• 12.7 References

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Table of Contents cont.

• 13  . Source Influence on Guided Wave Excitation
• 13.1 Introduction
• 13.2 Integral Transform Method
• 13.2.1 A Shear Loading Example
• 13.3 Normal Mode Expansion Method
• 13.3.1 Normal Mode Expansion in Harmonic
  Loading
• 13.3.2 Transient Loading Source Influence
• 13.4 Exercises
• 13.5 References

16
Table of Contents cont.

• 14. Horizontal Shear
• 14.1 Introduction
• 14.2 Dispersion Curves
• 14.3 Phase Velocities and Cutoff Frequencies
• 14.4 Group Velocity
• 14.5 Summary
• 14.6 Exercises
• 14.7 References

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Table of Contents cont.

• 15. Guided Waves in Anisotropic Media
• 15.1 Introduction
• 15.2 Phase Velocity Dispersion
• 15.3 Guided Wave Directional Dependency
• 15.4 Guided Wave Skew Angle
• 15.5 Guided Waves in Composites with Multiple
  Layers
• 15.6 Exercises
• 15.7 References

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Table of Contents cont.

• 16. Guided Wave Phased Arrays in Piping
• 16.1 Introduction
• 16.2 Guided Wave Phased Array Focus Theory
• 16.3 Numerical Calculations
• 16.4 Finite Element Simulation of Guided Wave
  Focusing
• 16.5 Active Focusing Experiment
• 16.6 Guided Wave Synthetic Focus
• 16.7 Synthetic Focusing Experiment
• 16.8 Summary
• 16.9 Exercises
• 16.10 References

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Table of Contents cont.

• 17  . Guided Waves in Viscoelastic Media
• 17.1 Introduction
• 17.2 Viscoelastic Models
• 17.2.1 Material Viscoelastic Models
• 17.2.2 Kelvin-Voight Model
• 17.2.3 Maxwell Model
• 17.2.4 Further Aspects of the Hysteretic and
  Kelvin-Voight Models
• 17.3 Measuring Viscoelastic Parameters
• 17.4 Viscoelastic Isotropic Plate
• 17.5 Viscoelastic Orthotropic Plate
• 17.5.1 Problem Formulation and Solution
• 17.5.2 Numerical Results
• 17.5.3 Summary
• 17.6 Lamb Waves in a Viscoelastic Layer
• 17.7 Viscoelastic composite Plate
• 17.8 Pipes with Viscoelastic Coatings
• 17.9 Exercises
• 17.10 References

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Table of Contents cont.

• 18. Ultrasonic Vibrations
• 18.1 Introduction
• 18.2 Practical Insights into the Ultrasonic
  Vibrations Problem
• 18.3 Concluding Remarks
• 18.4 Exercises
• 18.5 References

21
Table of Contents cont.

• 19. Guided Wave Array Transducers
• 19.1 Introduction
• 19.2 Analytical Development
• 19.2.1 Linear Comb Array Solution
• 19.2.2 Annular Array Solution
• 19.3 Phased Transducer Arrays for Mode Selection
• 19.3.1 Phased Array Analytical Development
• 19.3.2 Phased Array Analysis
• 19.4 Concluding Remarks
• 19.5 Exercises
• 19.6 References

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Table of Contents cont.

• 20. Introduction to Guided Wave Nonlinear Methods
• 20.1 Introduction
• 20.2 Bulk Waves in Weakly Nonlinear Elastic
  Media
• 20.3 Measurement of the Second Harmonic
• 20.4 Second Harmonic Generation Related to
  Microstructure
• 20.5 Weakly Nonlinear Wave Equation
• 20.6 Higher Harmonic Generation in Plates
• 20.6.1 Synchronism
• 20.6.2 Power Flux
• 20.6.3 Group Velocity Matching
• 20.6.4 Sample Laboratory Experiments
• 20.7 Applications of Higher Harmonic Generation
  by Guided Waves
• 20.8 Exercises
• 20.9 References

23
Table of Contents cont.

• 21. Guided Wave Imaging Methods
• 21.1 Introduction
• 21.2 Guided Wave through Transmission Dual Probe
  Imaging
• 21.3 A Defect Locus Map
• 21.4 Guided Wave Tomographic Imaging
• 21.5 Guided Wave Phased Array in Plates
• 21.6 Long-Range Ultrasonic Guided Wave Pipe
  Inspection Images
• 21.7 Exercises
• 21.8 References

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Table of Contents cont.
Appendix A Ultrasonic Nondestructive Testing
Principles, Analysis, and Display Technology

• A.1 Physical Principles
• A.2 Wave Interference
• A.3 Computational Model for a Single Point Source
• A.4 Directivity Function for a Cylindrical
  Element
• A.5 Ultrasonic Field Presentations
• A.6 Near-Field Calculations
• A.7 Angle-of-Divergence Calculations
• A.8 Ultrasonic Beam Control
• A.9 A Note of Ultrasonic Field
  Solution Techniques
• A.10 Time and Frequency Domain Analysis
• A.11 Pulsed Ultrasonic Field Effects
• A.12 Introduction to Display Technology
• A.13 Amplitude Reduction of an Ultrasonic
  Waveform
• A.14 Resolution and Penetration Principles
• A.14.1 Axial Resolution
• A.14.2 Lateral Resolution
• A.15 Phase Arrays and Beam Focusing
• A.16 Exercises
• A.17 References

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Table of Contents cont.

• Appendix B Basic Formulas and Concepts in the
  Theory of Elasticity
• B.1 Introduction
• B.2 Nomenclature
• B.3 Stress, Strain, and Constitutive Equations
• B.4 Elastic Constant Relationships
• B.5 Vector and Tensor Transformation
• B.6 Principal Stresses and Strains
• B.7 The Strain Displacement Equations
• B.8 Derivation of the Governing Wave Equation
• B.9 Anisotropic Elastic Constants
• B.10 References

26
Table of Contents cont.

• Appendix C Physically Based Signal Processing
  Concepts for Guided Waves
• C.1 General Concepts
• C.2 The Fast Fourier Transform (FFT)
• C.2.1 Example FFT Use Analytic Envelope
• C.2.2 Example FFT Use Feature Source for
  Pattern Recognition
• C.2.3 Discrete Fourier Transform Properties
• C.3 The Short Time Fourier Transform (STFFT)
• C.3.1 Example STFFT to Dispersion Curves
• C.4 The 2-D Fourier Transform (2DFFT)
• C.5 The Wavelet Transform (WT)
• C.6 Exercises
• C.7 References

27
Table of Contents cont.

• Appendix D Guided Wave Mode and Frequency
  Selection Tips
• D.1 Introduction
• D.2 Mode and Frequency Selection Considerations
• D.2.1 A Surface-Breaking Defect
• D.2.2 Mild Corrosion and Wall Thinning
• D.2.3 Transverse Crack Detection in the Head of
  a Rail
• D.2.4 Repair Patch Bonded to an Aluminum Layer
• D.2.5 Water-Loaded Structures
• D.2.6 Frequency and Other Tuning Possibilities
• D.2.7 Ice Detection with Ultrasonic Guided
  Waves
• D.2.8 Deicing
• D.2.9 Real Time Phased Array Focusing in Pipe
• D.2.10 Aircraft, Lap-Splice, Tear Strap, and
  Skin to Core Delamination Inspection
  Potential
• D.2.11 Coating Delamination and Axial Crack
  Detection
• D.2.12 Multilayer structures
• D.3 Exercises
• D.4 References

28
Background

• Preface
• To start now with Chapter 1. Lets see a few
  references first, of many listed in the book
  after each chapter.
• References
• Achenbach, J. D. (1976). Generalized continuum
  theories for directionally reinforced solids,
  Arch. Mech. 28(3) 25778.
• Achenbach, J. D. (1984). Wave Propagation in
  Elastic Solids. New York North-Holland.
• Achenbach, J. D. (1992). Mathematical modeling
  for quantitative ultrasonics, Nondestr. Test.
  Eval. 8/9 36377.
• Achenbach, J. D., and Epstein, H. I. (1967).
  Dynamic interaction of a layer of half space, J.
  Eng. Mech. Division 5 2742.
• Achenbach, J. D., Gautesen, A. K., and McMaken,
  H. (1982). Ray Methods for Waves in Elastic
  Solids. Boston, MA Pitman.
• Achenbach, J. D., and Keshava, S. P. (1967). Free
  waves in a plate supported by a semi-infinite
  continuum, J. Appl. Mech. 34 397404.
• Auld, B. A. (1990). Acoustic Fields and Waves in
  Solids. 2nd ed., vols. 1 and 2. Malabar, FL
  Krieger.
• Auld, B. A., and Kino, G. S. (1971). Normal mode
  theory for acoustic waves and their application
  to the interdigital transducer, IEEE Trans.
  ED-18 898908.

29
Background cont.

• Auld, B. A., and Tau, M. (1978). Symmetrical Lamb
  wave scattering at a symmetrical pair of thin
  slots, in 1977 IEEE Ultrasonic Sympos. Proc. vol.
  61.
• Beranek, L. L. (1990). Acoustics. New York
  Acoustical Society of America, American Institute
  of Physics.
• Davies, B. (1985). Integral Transforms and Their
  Applications. 2nd ed. New York Springer-Verlag.
• Eringen, A. C., and Suhubi, E. S. (1975). Linear
  Theory (Elastodynamics, vol. 2). New York
  Academic Press.
• Ewing, W. M., Jardetsky, W. S., and Press, F.
  (1957). Elastic Waves in Layered Media. New York
  McGraw-Hill.
• Federov, F. I. (1968). Theory of Elastic Waves in
  Crystals. New York Plenum.
• Graff, K. F. (1991). Wave Motion in Elastic
  Solids. New York Dover.
• Kino, C. S. (1987). Acoustic Waves Devices,
  Imaging and Digital Signal Processing. Englewood
  Cliffs, NJ Prentice-Hall.
• Kinsler, L. E., Frey, A. R., Coppens, A. B., and
  Sanders, J. V. (1982). Fundamentals of Acoustics.
  New York Wiley.
• Kolsky, H. (1963). Stress Waves in Solids. New
  York Dover.
• Love, A. E. H. (1926). Some Problems of
  Geodynamics. Cambridge University Press.
• Love, A. E. H. (1944a). Mathematical Theory of
  Elasticity. 4th ed. New York Dover.

30
Background cont.

• Love, A. E. H. (1944b). A Treatise on the
  Mathematical Theory of Elasticity. New York
  Dover.
• Miklowitz, J. (1978). The Theory of Elastic Waves
  and Waveguides. New York North-Holland.
• Mindlin, R. D. (1955). An Introduction to the
  Mathematical Theory of Vibrations of Elastic
  Plates. Fort Monmouth, NJ U.S. Army Signal Corps
  Engineers Laboratories.
• Musgrave, M. J. P. (1970). Crystal Acoustics. San
  Francisco, CA Holden-Day.
• Pollard, H. F. (1977). Sound Waves in Solids.
  London Pion Ltd.
• Rayleigh, J. W. S. (1945). The Theory of Sound.
  New York Dover.
• Redwood, M. (1960). Mechanical Waveguides. New
  York Pergamon.
• Rose, J. L. (1999). Ultrasonic Waves in Solid
  Media. Cambridge University Press.
• Rose, J. L. (2002). A baseline and vision of
  ultrasonic guided wave inspection potential,
  Journal of Pressure Vessel Technology 124
  27382.
• Stokes, G. G. (1876). Smiths prize examination,
  Cambridge. Reprinted 1905 in Mathematics and
  Physics Papers vol. 5, p. 362, Cambridge
  University Press.
• Viktorov, I. A. (1967). Rayleigh and Lamb Waves
  Physical Theory Applications. New York Plenum.

31
Major Contributors

• Michael Avioli
• Cody Borigo
• Jason Bostron
• Huidong Gao
• Cliff Lissenden
• Yang Liu

• Vamshi Chillara
• Jing Mu
• Jason Van Velsor
• Fei Yan
• Li Zhang

Dedication Aleksander Pilarski
32

• Wave propagation studies are not limited to NDT
  and SHM, of course. Many major areas of study in
  elastic wave analysis are under way, including
• (1) transient response problems, including
  dynamic impact loading
• (2) stress waves as a tool for studying
  mechanical properties, such as the modulus of
  elasticity and other anisotropic constants and
  constitutive equations (the formulas relating
  stress with strain and/or strain rate can be
  computed from the values obtained in various,
  specially designed, wave propagation
  experiments)
• (3) industrial and medical ultrasonics and
  acoustic-emission nondestructive testing
  analysis
• (4) other creative applications, for example, in
  gas entrapment determination in a pipeline, ice
  detection, deicing of various structures, and
  viscosity measurements of certain liquids and
• (5) ultrasonic vibration studies that combine
  traditional low-frequency vibration
  analysis tools in structural analysis with
  high-frequency ultrasonic analysis.

33

Figure 1-1 Comparison of bulk wave and guided
wave inspection methods.
34
Table 1.1 Ultrasonic Bulk vs. Guided Wave
Propagation Considerations
BULK GUIDED
Phase Velocities Constant Function of frequency
Group Velocities Same as phase velocities Generally not equal to phase velocity
Pulse Shape Non-dispersive Generally dispersive
35

• The principal advantages of using ultrasonic
  guided waves analysis techniques can be
  summarized as follows.
• Inspection over long distances, as in the
  length of a pipe, from a single probe position is
  possible. Theres no need to scan the entire
  object under consideration all of the data can
  be acquired from the single probe position.
• Often, ultrasonic guided wave analysis
  techniques provide greater sensitivity, and thus
  a better picture of the health of the material,
  than data obtained in standard localized normal
  beam ultrasonic inspection or other NDT
  techniques, even when using lower frequency
  ultrasonic guided wave inspection techniques.
• Continued on next slide

36

• Continued from previous slide
• The ultrasonic guided wave analysis techniques
  allow the inspection of hidden structures,
  structures under water, coated structures,
  structures running under soil, and structures
  encapsulated in insulation and concrete. The
  single probe position inspection using wave
  structure change and wave propagation controlled
  mode sensitivity over long distances makes these
  techniques ideal.
• Guided wave propagation and inspection are
  cost-effective because the inspection is simple
  and rapid. In the example described earlier,
  there would be no need to remove insulation or
  coating over the length of a pipe or device
  except at the location of the transducer tool.

37
Table 1.2 Ultrasonic Wave Considerations for
Isotropic vs. Anisotropic Media
ISOTROPIC ANISOTROPIC
Wave Velocities Not function of launch direction Function of launch direction
Skew Angles No Yes
38
Table 1.3 - A Comparison of the Currently Used
Ultrasonic Bulk Wave Technique and the Proposed
Ultrasonic Guided Wave Procedure for Plate and
Pipe Inspection
Bulk Wave Guided Wave
Tedious and time consuming Fast
Point by point scan (accurate rectangular grid scan) Global in nature (approximate line scan)
Unreliable (can miss points) Reliable (volumetric coverage)
High level training required for inspection Minimal training
Fixed distance from reflector required Any reasonable distance from reflector acceptable
Reflector must be accessible and seen Reflector can be hidden
39
Table 1.4. Natural Waveguides
Plates (aircraft skin)
Rods (cylindrical, square, rail, etc.)
Hollow cylinder (pipes, tubing)
Multi-layer structures
An interface
Layer or multiple layers on a half-space
40
Table 1.5. The Difference between SHM and
Non-Destructive Testing (NDT)

• SHM
• On-line evaluation
• Condition based maintenance
• Determine fitness-for-service and remaining
  useful time
• Less cost and labor
• Baseline required
• Environmental data compensation methods are
  required

• NDT
• Off-line evaluation
• Time base maintenance
• Find existing damage
• More cost and labor
• Baseline not available

41
Table 1.6. Successes Guided Waves in General
Increased computational efficiency developments and Understanding Basic Principles
Phased Array and Focusing developments in plates and pipes
Demonstration of optimal mode and frequency selections for penetration power, fluid loading influences, and other defect detection sensitivity requirements
42
Table 1.7 Successes Composite Materials
Understanding guided wave behavior in anisotropic media ( Slowness profiles and Skew angle influence)
Development of ultrasonic guided wave tomographic imaging methods
Comb sensor designs for optimal mode and frequency selection (linear comb and annular arrays)
43
Table 1.8 Successes Aircraft Applications
Demonstration of feasibility studies in composites and lap splice, tear strap, skin to core delamination, corrosion detection and other applications.
44
Table 1.9 Successes Pipe Inspection
Understanding and utilization of both axisymmetric and non-axisymmetric modes
Achieving excellent penetration power with special sensors, focusing, and mode and frequency choices
Handling fluid loading with Torsional Modes
Defect sizing accomplishments to less than 5 cross sectional area
Reduced false alarm calls in inspection due to focusing for confirmation
Circumferential location and length of defect estimations with focusing
Testing of Pipe under insulation, coatings, and/or soil
45
Table 1.10 Practical Challenges Guided Waves in
general
Modeling accuracy is critically dependent on accurate input parameters often difficult to obtain (especially for anisotropic and viscoelastic properties, interface conditions, and defect characteristics.)
Signal interpretations often difficult (due to multimode propagation and mode conversion, along with special test structure geometric features)
Sensor robustness to environmental situations like temperature, humidity to high stress, mechanical vibrations, shock and radiation
Adhesive bonding challenges for mounting sensors and sustainability in an SHM environment
Merger of guided wave developments with energy harvesting and wireless technology
Penetration power requirements
46
Table 1.11 Practical Challenges Composite
Materials
Dealing with complex anisotropy and wave velocity and skew angle as a function of direction
Viscoelastic influences
Penetration power due to anisotropy, viscoelasticity, and inhomogeneity
Differentiating critical composite damage such as delamination defects from structural variability during fabrication (including minor fiber misalignments, ply-drops, inaccurate fiber volume fraction, and so on)
Guided wave inspection of composites with unknown material properties.
47
Table 1.12 Practical Challenges Aircraft
Applications
Robustness of guided wave sensors under in-flight conditions
Influences of aircraft paint and embedded metallic mesh in composite airframes for lightning protection
48
Table 1.13 Challenges Pipe Inspection
Tees, elbows, bends, and number of elbows and inspection beyond elbows
Quantification in defect location, characterization, sizing, especially depth determination
Inspection reliability and false alarms (due to multimode propagation, mode conversions, and so many pipe features like welds, branches, etc.)
Reducers, expanders, unknown layout drawings, cased pipes and sleeves