As a general criterion in resistance spot-welding, the spot weld nugget must have a diameter of 5*t^(1/2), in which "t" is the diameter of the welding sheet. For instance, spot welding two 1-mm sheets together should result in a weld of 5-mm diameter. You can measure this diameter, non-destructively, using Lamb waves through-transmission technique, which involves measuring the width of the zone through which attenuated waves are observed.
Instructions
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1
Use the ultrasound to transmit ultrasonic waves at a "sending point," outside the nugget.
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2
Use the receiver to receive "transmitted waves," at a "receiving point" opposite to the sending point.
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3
Detect and display the through-transmitted ultrasonic waves, using a signal-processing computer application.
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Measure the width of the zone where highly attenuated through-transmitted waves are observed. This width is equal to the nugget diameter.