1) Ultrasonic testing techniques include pulse echo, through transmission, and transmission with reflection. Pulse echo uses a single probe to send and receive sound to detect defect depth and orientation. Through transmission uses probes on opposite sides to detect defects but not location. Transmission with reflection can locate defects. 2) The sound beam has a near zone where intensity varies and a far zone with exponential decay. The near zone length depends on probe frequency and diameter, with higher frequency and larger diameter increasing length. 3) Beam spread is smaller with higher frequency and larger diameter probes. Compression waves have a smaller beam spread than shear waves. Snell's law and critical angles determine how sound refracts between materials

1. Ultrasonic Testing Part 2 TWI

4. Defect Position No indication from defect A (wrong orientation) A B B

5. Through Transmission Technique Transmitting and receiving probes on opposite sides of the specimen Presence of defect indicated by reduction in transmission signal No indication of defect location Fail safe method Tx Rx

8. Transmission with Reflection Also known as: Tandem Technique or Pitch and Catch Technique R T

11. Ideal Pulse Length 5 cycles for weld testing

13. The Sound Beam NZ FZ Main Beam Distance Intensity varies Exponential Decay

14. Main Lobe Side Lobes Near Zone Main Beam The main beam or the centre beam has the highest intensity of sound energy Any reflector hit by the main beam will reflect the high amount of energy The side lobes has multi minute main beams Two identical defects may give different amplitudes of signals

16. Near Zone

19. Which of the above probes has the longest Near Zone ? 1 M Hz 5 M Hz 1 M Hz 5 M Hz

22. Beam Spread Edge,K=1.22 20dB,K=1.08 6dB,K=0.56 Beam axis or Main Beam

25. Which of the above probes has the Largest Beam Spread ? 1 M Hz 5 M Hz 1 M Hz 5 M Hz

27. Testing close to side walls

29. The Phenomenon of Sound REFLECTION REFRACTION DIFFRACTION

30. The Phenomenon of Sound REFLECTION REFRACTION DIFFRACTION

32. Inclined incidence(not at 90 o ) Incident Transmitted The sound is refracted due to differences in sound velocity in the 2 DIFFERENT materials

35. Snell’s Law I R Material 1 Material 2 Incident Refracted Normal

36. Snell’s Law C Perspex Steel C 20 48.3

37. Snell’s Law C Perspex Steel C 15 34.4

38. Snell’s Law C Perspex Steel C 20 S 48.3 24

39. Snell’s Law Perspex Steel S C C When an incident beam of sound approaches an interface of two different materials: REFRACTION occurs There may be more than one waveform transmitted into the second material, example: Compression and Shear When a waveform changes into another waveform: MODE CHANGE C C S

40. Snell’s Law Perspex Steel C If the angle of Incident is increased the angle of refraction also increases Up to a point where the Compression Wave is at 90 ° from the Normal 90 ° This happens at the FIRST CRITICAL ANGLE C S C S C S

41. 1st Critical Angle C 27.4 S 33 C Compression wave refracted at 90 degrees

42. 2nd Critical Angle C S (Surface Wave) 90 C Shear wave refracted at 90 degrees 57 Shear wave becomes a surface wave

43. 1st Critical Angle Calculation C Perspex Steel C S 27.2

44. 2nd Critical Angle Calculation C Perspex Steel C S 57.4

45. 1 st . 2 nd . 33 ° 90 ° Before the 1 st . Critical Angle : There are both Compression and Shear wave in the second material At the FIRST CRITICAL ANGLE Compression wave refracted at 90 ° Shear wave at 33 degrees in the material Between the 1 st . And 2 nd . Critical Angle: Only SHEAR wave in the material. Compression is reflected out of the material. At the 2 nd . Critical Angle : Shear is refracted to 90 ° and become SURFACE wave Beyond the 2 nd . Critical Angle: All waves are reflected out of the material. NO wave in the material. S C C