![Perpendicular Incidence of Sound
Waves
Z2-Z1
Z2+Z1
[ ]
2
RE =
DE =
4Z2Z1
(Z2+Z1)2](https://image.slidesharecdn.com/ultrasonicslevel3a-240505072829-c29f71ec/85/Ultrasonics-testing-Level-3A-presentation-ppt-21-320.jpg)
![Piezoelectric Terms
Applied Voltage [U] r = receive, t = transmit
Change in thickness [ Δx]
Piezoelectric modulus [d33]
The higher the value the greater the thickness
variation for a given voltage
Δx = d33 Ut](https://image.slidesharecdn.com/ultrasonicslevel3a-240505072829-c29f71ec/85/Ultrasonics-testing-Level-3A-presentation-ppt-48-320.jpg)
![Piezoelectric Terms
Piezoelectric pressure constant [g33]
Sound Pressure [p]
Thickness [d]
Ur = g33dpx](https://image.slidesharecdn.com/ultrasonicslevel3a-240505072829-c29f71ec/85/Ultrasonics-testing-Level-3A-presentation-ppt-49-320.jpg)
![Piezoelectric Terms
Mechanical Quality [Q]
Measure of Oscillation loss, the lower
the value the higher the rate of absorption the
less backing material is required.
Acoustic Impedance [Z]
Z = ρV
For Complete transmission Z1 = Z2](https://image.slidesharecdn.com/ultrasonicslevel3a-240505072829-c29f71ec/85/Ultrasonics-testing-Level-3A-presentation-ppt-50-320.jpg)
Ultrasonics testing Level 3A presentation .ppt
- 1. Ultrasonics Level 3 • Fundamentals of Sound • Piezoelectric Materials • Composite and Phased Array Transducers • Other Transducers • Pulse Echo Systems • Transit Time Methods • Shadow Methods • Imaging • Scanning Methods • General Testing Procedures • Evaluation Methods • Ultrasonic Techniques • Codes and Standards
- 2. Fundamentals of Sound Consider from two points of view Material parameters Wave Parameters
- 3. Material Parameters Particle Displacement Particle Velocity Modulus of Elasticity Density
- 4. Particle Displacement Total length movement of one discrete particle. In metals very small compared to wave length displacement α sound pressure impedance
- 5. Particle Velocity The rate at which a discrete particle oscillates Velocity = Modulus of Elasticity Density
- 6. Modulus of Elasticity The ratio of stress to strain within a material Used in engineering to determine the amount of deformation for a given load. Modulus of Elasticity = Stress Strain
- 7. Density Mass per unit volume (Density = mass/volume) As density increases velocity decrease for a given Modulus of Elasticity
- 8. Sound Attenuation Loss of sound as it travels through a material Caused by: Scatter Absorption Beam Spread
- 9. Wave Parameters Wave length Frequency Sound Pressure Wave Velocity
- 10. Wave Length Is the distance between two planes in which the particles are in the same state of motion. λ = velocity frequency
- 13. Effect of Diameter and Frequency on Beam Profile
- 14. Review Profile Formulas Near Zone = D2F/4V Sin (1/2 Angle Beam Divergence) = V*1.22/DF (absolute edge) = V*1.08/DF (20dB edge) = V*.56/DF (6dB edge)
- 16. Beam Cross-section Max energy at beam centre 50% energy loss 90% energy loss Total energy loss Beam can be elliptical typically from angle probes View on X-X
- 17. Beam Spread Calculation Sin q = K . l D K = constant factor 50% edge = 0.56 90% edge = 1.08 Extreme edge = 1.22 D = crystal diameter l = wavelength q EG: 1.22 x 1.5mm 10mm = 1.83 10 = 0.183 Inverse sine 0.183 = 10.50
- 18. Review Sound Pressure Formulas Relative measure of sound pressure in dB = 20 log10 (h1/h2) Where h1 and h2 are the screen heights being compared
- 19. Review Question Material is steel, the transducer is 12mm, 5.0 MHz Calculate: Beam spread (absolute edge) Wave length Near Zone
- 20. Answer Beam Spread Sin Φ = 1.2 V/DF = 1.2 * .5890*106 / 1.2*5*106 = .117 Φ = 6.8° (1/2 angle) λ = V/F =.12 cm NZ = D2F/4V =(1.2)2*5*106/4*.5890*106 =3.67 cm
- 21. Perpendicular Incidence of Sound Waves Z2-Z1 Z2+Z1 [ ] 2 RE = DE = 4Z2Z1 (Z2+Z1)2
- 22. Refraction Sin θ1 = Sin θ2 V1 V2 Snell’s Law
- 23. No Refraction
- 24. < 1st Critical Angle
- 25. At 1st Critical Angle
- 26. > 1st Critical Angle
- 27. At 2nd Critical Angle
- 28. Refraction / Multiple Boundaries OR
- 29. Sound Pressures After Refraction Incident range 25.6° to 61° Refracted range 30° to 80° Optimum refracted range 32° to 60°
- 30. Critical Angles As a result of refraction At the first critical angle Compressional wave is refracted 90° At the second critical angle Compressional wave is totally reflected Shear wave is refracted 90° Above the second critical wave Both the compressional and shear waves are totally reflected
- 31. Application of Refracted Waves Although most ultrasonics are conducted either normal to the surface (without refraction) or between the first and second critical angles there are other applications. Travel is parallel to the surface Velocity equal to compressional wave in same material Highly attenuated, shear waves are continuously being generated
- 32. Longitudinal Creeping Waves Sometimes referred to as a head wave
- 34. Creep Wave Probe Primary Creep Wave Secondary Creep Wave 85 deg. longitudinal Transverse Longitudinal Cp.
- 35. Time of Flight Diffraction
- 36. Diffraction Thomas Young, 1802 Bending of sound (or light) behind an obstacle, in accordance with Huygen’s Principle and is an interference phenomenon.
- 37. Interaction of Wave with a Crack-Like Defect
- 38. Time of Flight Diffraction to Size a Defect
- 39. Diffraction Techniques Time of Flight Diffraction When the forward diffracted wave is used Reflected Tip Diffraction When the backward diffracted wave is used
- 40. Piezoelectric Sound Generation • 1880, Currie Brothers • No single centre of Symmetry • 32 Classes of Crystal Structures • 21 of 32 do not have Centre of Symmetry • 20 of 21 classes are Piezoelectric
- 41. Sintered Ceramic Crystals Above the Currie Temp Below the Currie Temp
- 42. Sintered Ceramic Crystals Crystals that display this property of being distorted are referred to as ferro-electric and have a dipole moment. Not on an atomic level like a natural piezoelectric crystal Sintered ceramic heated above curie temperature polarized by a strong electric field cooled below curie temperature If heated near the curie temperature the ferro-electric property is lost
- 43. Function Applied stress (compression or tension) in the direction of Polarization Shifts the centre points of the structure electric charge Resulting in a electric charge on the surface of the crystal Metal films (electrodes) conduct charge which is proportional to the stress
- 44. Polarization
- 45. Polarization
- 46. Polarization Three dimensional movement Not always uniform, effected by edges Thickness proportional to Natural Frequency
- 48. Piezoelectric Terms Applied Voltage [U] r = receive, t = transmit Change in thickness [ Δx] Piezoelectric modulus [d33] The higher the value the greater the thickness variation for a given voltage Δx = d33 Ut
- 49. Piezoelectric Terms Piezoelectric pressure constant [g33] Sound Pressure [p] Thickness [d] Ur = g33dpx
- 50. Piezoelectric Terms Mechanical Quality [Q] Measure of Oscillation loss, the lower the value the higher the rate of absorption the less backing material is required. Acoustic Impedance [Z] Z = ρV For Complete transmission Z1 = Z2
- 51. Ceramic Piezoelectric Materials Barium Titanate Lead Zirconate Titanate Lead Titanate Lead Meta-niobate Barium Sodium Niobate
- 57. Immersion Probes
- 59. Delay Tip Probes
- 61. Captive Water Column Probe water column cable flexible membrane nugget electrode mark transmitted pulse reflected pulse transducer
- 62. Composite Transducers E.g.. Paul Mayer, Krautkramer, ceramic rods in a polymer matrix
- 64. Focusing Linear Phased Array
- 65. Focusing Linear Phased Array
- 66. Focusing Linear Phased Array
- 67. Dynamic Focussing Mechanical Displacement c = velocity in material FOCUS DEPTH (PULSER) DYNAMIC FOCUSING (RECEIVER) Beam displacement
- 68. Variable Focal Length Linear Phased Array
- 70. Steering Linear Phased Array
- 71. Steering Linear Phased Array
- 73. Linear Scanning
- 76. Annular Array
- 77. Phased Array
- 78. Scanning and Focusing Phased Arrays
- 79. Focusing, Scanning Shear Wave Phased Array
- 81. Other Methods of Transmitting and Receiving Sound Piezoelectric Indirect method, i.e. coupled Direct Methods Surface forms part of the transducer Coupling layers can interfere with the transmission and reception of sound Piezoelectric elements have their own natural frequency, Which modify the output of sound
- 82. Mechanical Transducers e.g. of transmission electro mechanical hammer (for concrete) or rotating wire brush (for honey comb bonding) Reception of this sound might be by pressure sensitive liquid crystals
- 83. Thermal Transducers Heat shock thermal expansion and mechanical stresses which initiate sound Short duration, High Frequency Micro wave, infrared, visible UV (electromagnetic) Electron beam (corpuscular)
- 84. Laser Transducers 1 to 100 MHz Large operational distances up to 10m Generated pulse is independent of incident angle
- 85. Electrostatic Transducers Direct or indirect through a coupling liquid
- 87. Electromagnetic Acoustic Transducers Permanent Magnet (or electromagnet) produces a steady field Coil which carries an RF current Induces a eddy currents into the surface of the part Eddy Currents interact with the steady field to produce Lorentz forces Lorentz forces cause part to vibrate in sympathy with the RF signal When receiving energy the vibrating part acts like a moving conductor in a magnetic field which produces electricity
- 88. Electromagnetic Acoustic Transducers Lorentz Force Electromagnetic force on a moving charge EMATs Allow noncontact generation and reception of sound Although the power output is 40to 50 dB less than Barium Titanate the power can be increased Typical gaps at 2 MHz are about 1.0 to 1.5 mm
- 89. Magnetostriction Transducers Most ferromagnetic materials change shape in magnetic fields Change in shape is both volumetric and linear Below the Curie point of the material linear is much more significant Direct Excitation
- 90. Magnetostriction Transducers Can be used to excite the part directly or indirectly Magnetostrictive Transducer (for indirect excitation) Focused Transducer
- 91. Laser Excited Transducers Sound deflection methods Physical displacement method Advantages High resolution Allow work on hot surfaces Insensitive to electrical interference A scan of a 1.2 mm plate
- 92. Laser Excited Transducers The deflections cell is filled with a liquid as sound travels through the liquid it acts as a moving optical grating The grating acts as a phase grating effected by wave length and sound pressure
- 93. Laser Excited Transducers Laser Test Piece Lens for rough surfaces Beam Splitter Reference Mirror Photoelectric Cell Michelson Interferometer
- 95. Repetition Frequency Generator Purpose Trigger the transmitter pulse Start the sweep RFG Voltage Transmitted Pulse Echo Pattern Delay
- 96. Repetition Frequency Generator Sweep Voltage CRT Brightness Sweep Delay Working Time Interval Time
- 97. Repetition Frequency Generator Delay of Transmitted Pulse Delayed to ensure initial pulse is visible Can lead to an error in measuring thickness (zero error) Error effect eliminated by using multiple echoes for measurement and calibration
- 98. Repetition Frequency Generator Maladjustment When the repetition rate is too high for the sound path Spurious Indications Most instruments have the repetition rate switched with the range Maintain sufficient brightness and avoid spurious indications
- 99. Transmitter Generates a voltage of approximately 100 Volts Pulse shape and frequency is modified by the transducer
- 100. Receiver Range 30µ volts to 30volts Dynamic range 120 dB, quick recovery Voltage limiter Course Gain Control Preamp Fine Gain Control Main Amplifier Signal Treatment (rectifier, video filter, suppression,differentiation) Video Amplifier Output
- 101. Gates Monitor a depth range for echoes Signal is compared to a threshold voltage and logic circuit alarms Can be more than one Can be used to monitor back echo Fixed on screen, fixed to an echo, slave Digital information available: amplitude , time Usually displayed on screen
- 102. Distance Amplitude Correction Two methods 1. Distance dependant threshold Response voltage decreases with sweep voltage 2. Swept Gain Amplification increases with distance
- 103. Distance Amplitude Correction Manually adjusted based on artificial flaws at different depths Up to 8 linear sweep sections Can be a computer learned function, based on stored DGS curves for transducer diameter, frequency and material attenuation.
- 104. Purpose: Graphically compensates for material attenuation, nearfield effects, beam spread, and surface roughness. GAIN 47.0dB REJ 0% AMP. DAC 145% RANGE 0.200 in/div 20 40 60 80 100 FILENAME.023 ID>100 GATE1 ALARM F1=DRAW DAC, F2=DONE, F3=CLEAR CURRENT 42% ASME FORMAT DAC CURVE NOTE: Reflectors of the same size will produce echoes which peak along that curve despite different locations within the test piece. DAC CURVE D.A.C.
- 105. Purpose: Compensates for the changes in echo amplitude from equal size reflectors at different distances due to attenuation and beam spreading. TVG SETUP NOTE: Reflectors of the same size will produce indications of equal screen height regardless of their distance in the material. MIN DEPTH 0.990 1.000 in GAIN 47.0dB REJ 0% RANGE 0.200 in/div 20 40 60 80 100 FILENAME.023 ID>100 GATE1 ALARM 0 2 4 6 8 10 TVG T.V.G. or T.C.G.
- 106. Instrument Technical Characteristics Precision of Echo Amplitude Calibrated Gain precision Vertical linearity Stability of transmitter voltage Precision of Distance Linearity of time base Stability of PRR to sweep Width of screen Precision possible in reading the screen Transducer sound field damping index points (angle beam)
- 107. Instrument Technical Characteristics Sensitivity Transmitter energy Limiting sensitivity of amplifier (noise & bandwidth) Shape of the sound field Damping and coupling losses Depth Resolution Quality of transducer, frequency, damping, suppression of reverberation Rise time of transmitter Amplifier Characteristics
- 108. Transit Time Methods Wall thickness Sound velocity Physical strain
- 109. Time Measurement Comparing it with a known (Two parallel circuits, adjusting the known) Integration method (Measuring between 2 successive echoes, not the first) Counting method Measuring oscillation counts between reflections
- 110. Potential Errors Time Measurement Detour Error Transmit/receive transducer, V-shaped path At Lower Limit of Range Signal Signal may be too low to trigger gate Surface wave cross coupling on rough surfaces
- 111. Other Methods Frequency Methods Resonance thickness testing Shadow Methods Through transmission
- 112. Imaging Methods Liquid Surface Relief Method Referred to as a Scanning Laser Acoustic Microscope light is more or less deflected by the surface distortions, resolution in order of 1 wave length
- 113. Imaging Methods Ultrasonovision (RCA) Metallic diagram being scanned by a laser system, transparent mirror work as interferometer. Variations in light intensity make up the image.
- 114. Scanning Methods A, B & C
- 115. A Scan Time or Distance Amplitude
- 116. dB ITEM SELECT GATE WIDTH PULSER FREEZE SAVE GATE LEVEL ZERO OFFSET RANGE VEL1 ZOOM ANGLE 2nd F OPTION SELECT F1 F2 F3 PRINT SEND DEPTH %AMP REF MEMORY THICK ALARM VEL2 WAVE REJECT PEAK MEM GATE START GATE2 ON OFF DISPLAY STATUS 2 7 1 4 ID 6 5 9 8 MEMO 0 3 > < ALPHA # DELETE ABC DEF GHI JKL MNO PRS TUV WXY QZ SYMBOL PANAMETRICS EPOCH III B-SCAN Encoded Information Encoded Modes document distance traveled and corresponding depth information for all points along the B-SCAN. Test Sample Encoder Transducer Cable Encoder Cable Couplant Feed Connector Probe Holder EPOCH III ENCODER SETUP
- 117. F1=STOP, F2=ASCAN, F3=NEWSCAN < DT 6.16 in B GAIN 55.0dB < DT 6.16 in MIN DEPTH 1.090 RANGE 1.200 in DELAY 0.800 in 0.800 2.000 B I D I R 1.090 in A ID> 50 B-SCAN Display The B-SCAN will continue to run if the encoder is moved until: - The scan is stopped or a new scan in initiated - The memory buffer becomes full (See “EPOCH III Memory & Datalogger”) Flashing “A” indicates alarm condition is present Current thickness reading at cursor is displayed Cursor indicates current measurement point Encoder Directional Arrow and Distance Traveled value (also shown below)
- 118. C Scan Image Format Plan view of defective area
- 119. 3D Image Format
- 120. Scanning Methods P Scan (Projected Image Scanning System) Developed by Danish Welding Institute Mechanical scanning, mechanical probe position measurements
- 121. Scanning Methods SUTAR Similar to P Scan, also provides tabular data Transducer positions are measured by air borne ultrasonics Phased Array
- 122. Scanning Methods Acoustic Holography Two step process 1. Capturing and storing image in a single plane 2. Recreating the image in multi-plane space
- 123. Scanning Methods Holography (Relief Method) Reference Phase Hologram
- 124. Scanning Methods Reference created electronically
- 125. Acoustic Holography Two Dimensional Reconstruction
- 126. General Testing Procedures Convex Reduced contact surface area (rectangular) Increased divergence Drop in sensitivity Angle of refraction may increase (shear wave)
- 128. Convex Contact Surface Freq Transducer Radius Drop in Dia of Curviture Sensitivity MHz Inches Inches dB 1 0.5 4 15 1 0.5 20 6 2 1 4 15 2 1 20 4 2 0.375 4 3 2 0.375 20 0 4 1 4 15 4 1 20 4 4 0.375 4 6 4 0.375 20 1
- 129. Convex Contact Surface With a curved shoe Angle of incidence changes with circumference At higher angles (e.g. 70°) surface waves may result
- 130. Concave Surfaces Contact may be difficult or impossible Best done with immersion and focal lens If it must be contact use a focal lens and adapter piece
- 131. General Testing Procedures Considerations Rough surfaces Higher viscosity Premature drying Ease of Removal Damage to component (e.g. Corrosion) Wet ability of surface Cost Toxicity Cleanliness Acoustic Impedance Uniformity
- 132. Coupling Coupling can occur on smooth surfaces, with force Free flowing water can be used up to 250° C High velocity water into a gap can be used up to 400° C Alternates Water gap Water delay lines Immersion
- 133. Confirming Coupling Back echo Sliding resistance Grass on the base line Automatically controlled Corrective gain, using a back echo Second transducer (receiving)
- 134. Boundaries and Complex Paths Boundaries Parallel to Sound Path 33°
- 135. Boundaries Parallel to Sound Path 4MHz, 10mm dia, flaw depth 840mm, small constant size reflector Caused by a phase shift in the reflected longitudinal wave.
- 136. Small Fatigue Cracks From a Parallel Surface High Frequency Large Diameter Transducer Positioned away from the side wall Because of the edge effects Back echoes cannot be used to judge defect size.
- 137. Triangular Reflection Without mode conversion With mode conversion Distance traveled = 1.3d Apparent distance traveled= 1.67d (steel) & 1.78 (aluminum)
- 138. Interference Echoes
- 139. Interference Echoes
- 140. Interference Echoes
- 141. Applied Ultrasonics Flaws and inclusions generally in the direction parallel to grain flow therefore UT beam should be perpendicular to grain flow
- 142. Applied Ultrasonics Consider the echo dynamics as the transducer is moved
- 143. Applied Ultrasonics Consider the echo patterns
- 144. Applied Ultrasonics Position beam to hit the fatigue crack at close to perpendicular and avoid interference echoes
- 145. Applied Ultrasonics Consider the shape and orientation of the discontinuities and the limitations of the techniques available
- 146. Applied Ultrasonics Considerations Rough surfaces (coupling losses) Course Grain Structure ((scattering and attenuation) T/R transducers (improve near surface resolution) Angle probes (angles maybe different because of velocity difference) Angle probes may improve defect detection (corner reflectors) Highly Damped transducers (reduce the scatter noise)
- 148. Applied Ultrasonics Conventional transducer Highly damped transducer
- 149. Applied Ultrasonics Usually shear wave, the thinner the members the higher the angle Consider Code requirements Laminations in the plate Possible orientations of the flaws External geometry (e.g. backing bars) Defect size and shape CSA W59-1989
- 150. Applied Ultrasonics Detection of the lack of bond
- 151. Applied Ultrasonics If the layers being bonded are not of equal thickness the bond can be monitored by watching the back echo If signal processing is used, Fourier Transforms can be used to measure bond line thickness and detect lack of bond
- 152. Evaluation Methods DGS Diagrams Mapping Comparison to reference standards Historical acceptance standards
- 153. Evaluation Methods Reference Standards All ultrasonic procedures should be based on a reference standard If there is more than one reference standard they must display the same ultrasonic response It may be appropriate to have more than one standard in case it becomes damaged or lost Attenuators must be calibrated periodically Equipment must be periodically checked against the reference standard Caution must be taken when comparing a discontinuity against a artificial reflector
- 154. Evaluation Methods Involves looking at reflected pulse with a frequency analyzer It finds uses in microstructure characterization, determining mean grain size and porosity. It is used in bond testing and composite laminate testing to reveal features that cannot be easily identified in the time domain.
- 155. Codes and Standards ASTM E317 Performance of Pulse Echo Testing Systems ASTM E797 Measuring Thickness with Pulse Echo ASTM E273 Ultrasonic Inspection of Longitudinal Welded Pipe ASTM E1315 Ultrasonic Examination on Curved Surfaces ASTM A609 Ultrasonic Examination of Some Castings ASTM E1065 Evaluating Ultrasonic Search Units CSA W59 Welded Construction (Ultrasonic portion, dynamic structures)
- 156. The End