770 likes | 1.23k Views
Basic Principles of Ultrasonic Testing Theory and Practice. Examples of oscillation. ball on a spring. pendulum. rotating earth. Pulse. The ball starts to oscillate as soon as it is pushed. Oscillation. Movement of the ball over time. Frequency. Time. One full oscillation T.
E N D
Basic Principles of Ultrasonic Testing Theory and Practice Krautkramer NDT Ultrasonic Systems
Examples of oscillation ball ona spring pendulum rotatingearth Krautkramer NDT Ultrasonic Systems
Pulse The ball starts to oscillate as soon as it is pushed Krautkramer NDT Ultrasonic Systems
Oscillation Krautkramer NDT Ultrasonic Systems
Movement of the ball over time Krautkramer NDT Ultrasonic Systems
Frequency Time One full oscillation T From the duration of one oscillation T the frequency f (number of oscillations per second) is calculated: Krautkramer NDT Ultrasonic Systems
The actual displacement a is termed as: a Time 0 90 180 270 360 Phase Krautkramer NDT Ultrasonic Systems
Spectrumofsound Example Frequency range Hz Description Infrasound 0 - 20 Earth quake 20 - 20.000 Audible sound Speech, music > 20.000 Ultrasound Bat, Quartz crystal Krautkramer NDT Ultrasonic Systems
Atomic structures liquid gas solid • low density • weak bonding forces • medium density • medium bonding forces • high density • strong bonding forces • crystallographic structure Krautkramer NDT Ultrasonic Systems
Understanding wave propagation: Ball = atom Spring = elastic bonding force Krautkramer NDT Ultrasonic Systems
start of oscillation T distance travelled Krautkramer NDT Ultrasonic Systems
During one oscillation T the wave front propagates by the distance : T Distance travelled From this we derive: Wave equation or Krautkramer NDT Ultrasonic Systems
Sound propagation Longitudinal wave Direction of propagation Direction of oscillation Krautkramer NDT Ultrasonic Systems
Direction of propagation Sound propagation Transverse wave Direction of oscillation Krautkramer NDT Ultrasonic Systems
330 m/s AirWaterSteel, longSteel, trans 1480 m/s 5920 m/s 3250 m/s Wave propagation Longitudinal waves propagate in all kind of materials. Transverse waves only propagate in solid bodies. Due to the different type of oscillation, transverse wavestravel at lower speeds. Sound velocity mainly depends on the density and E-modulus of the material. Krautkramer NDT Ultrasonic Systems
Reflection and Transmission As soon as a sound wave comes to a change in material characteristics ,e.g. the surface of a workpiece, or an internal inclusion, wave propagation will change too: Krautkramer NDT Ultrasonic Systems
Behaviour at an interface Medium 1 Medium 2 Incoming wave Transmitted wave Reflected wave Interface Krautkramer NDT Ultrasonic Systems
Reflection + Transmission: Perspex - Steel 1,87 1,0 Transmitted wave Incoming wave 0,87 Reflected wave Perspex Steel Krautkramer NDT Ultrasonic Systems
Reflection + Transmission: Steel - Perspex Transmitted wave Incoming wave 1,0 0,13 -0,87 Reflected wave Steel Perspex Krautkramer NDT Ultrasonic Systems
Amplitude of sound transmissions: Copper - Steel Steel - Air Water - Steel • Strong reflection • Double transmission • No reflection • Single transmission • Strong reflection with inverted phase • No transmission Krautkramer NDT Ultrasonic Systems
+ Piezoelectric Effect Battery Piezoelectrical Crystal (Quartz) Krautkramer NDT Ultrasonic Systems
+ Piezoelectric Effect The crystal gets thicker, due to a distortion of the crystal lattice Krautkramer NDT Ultrasonic Systems
+ Piezoelectric Effect The effect inverses with polarity change Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect Sound wave withfrequency f U(f) An alternating voltage generates crystal oscillations at the frequency f Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect Short pulse ( < 1 µs ) A short voltage pulse generates an oscillation at the crystal‘s resonant frequency f0 Krautkramer NDT Ultrasonic Systems
Reception of ultrasonic waves A sound wave hitting a piezoelectric crystal, induces crystal vibration which then causes electrical voltages at the crystal surfaces. Electrical energy Piezoelectrical crystal Ultrasonic wave Krautkramer NDT Ultrasonic Systems
Delay / protecting face socket Electrical matching crystal Cable Damping Straight beam probe TR-probe Angle beam probe Ultrasonic Probes Krautkramer NDT Ultrasonic Systems
100 ns RF signal (short) Krautkramer NDT Ultrasonic Systems
RF signal (medium) Krautkramer NDT Ultrasonic Systems
Focus Angle of divergence Crystal Accoustical axis 6 D0 N Near field Far field Sound field Krautkramer NDT Ultrasonic Systems
0 2 4 6 8 10 Ultrasonic Instrument Krautkramer NDT Ultrasonic Systems
- + U h 6 10 0 2 4 8 Ultrasonic Instrument Krautkramer NDT Ultrasonic Systems
- + U h 0 2 4 6 8 10 Ultrasonic Instrument Krautkramer NDT Ultrasonic Systems
+ U v - - + U h 0 2 4 6 8 10 Ultrasonic Instrument Krautkramer NDT Ultrasonic Systems
amplifier screen horizontal sweep IP BE clock pulser probe work piece Block diagram: Ultrasonic Instrument Krautkramer NDT Ultrasonic Systems
Sound reflection at a flaw s Probe Sound travel path Flaw Work piece Krautkramer NDT Ultrasonic Systems
IP BE F 0 2 4 6 8 10 delamination plate IP = Initial pulse F = Flaw BE = Backwall echo Plate testing Krautkramer NDT Ultrasonic Systems
Wall thickness measurement s s Corrosion 0 2 4 6 8 10 Krautkramer NDT Ultrasonic Systems
Through transmission signal 1 T R 1 2 T R 2 0 2 4 6 8 10 Flaw Through transmission testing Krautkramer NDT Ultrasonic Systems
a = s sinß F a' = a - x ß = probe angle s = sound path a = surface distance a‘ = reduced surface distance d‘ = virtual depth d = actual depth T = material thickness s d' = s cosß 0 20 40 60 80 100 d = 2T - t' a x a' d ß Lack of fusion s Work piece with welding Weld inspection Krautkramer NDT Ultrasonic Systems
Direct contact, single element probe Direct contact, dual element probe Fixed delay Through transmission Immersion testing Straight beam inspection techniques: Krautkramer NDT Ultrasonic Systems
IP IP 1 2 IE IE BE BE F 2 4 6 8 10 0 2 4 6 8 10 0 Immersion testing 1 2 surface = sound entry water delay backwall flaw Krautkramer NDT Ultrasonic Systems