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
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
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
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