The effect of sub surface defects in surface roughness monitoring through ultrasonic
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19-02-2011, 10:49 AM
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The effect of sub surface defects in surface roughness monitoring through ultrasonic flaw detector.
To study the effect of sub surface defects in surface roughness monitoring through ultrasonic flaw detector.
To study the sizing of defects.
• All sound waves, whether audible or ultrasonic, are mechanical vibrations involving movement of the medium in which they are traveling. A sound wave may be transmitted through any material which behaves in an elastic manner.
• Ultrasonic waves are classified on the basis of the mode of vibration of the particles of the medium with respect to the direction of propagation of the waves, namely longitudinal, transverse, and surface waves.
• A longitudinal stress wave propagates or traveling through coupling medium and touches surface of the engineering work piece will lose the energy due to attenuation.
• There are three basic reasons for loss of energy, namely beam spreading, absorption, and scattering.
• The surface roughness of work piece attenuates the ultrasound waves and this scattering is a measure of surface roughness.
• This behavior can account for a loss in amplitude of ultrasonic waves.
• Such energy loss of the ultrasonic waves can be correlated with surface roughness of work piece which is machined by grinding process.
Reflected Signals For Various Conditions
1.The roughness is conventionally measured by roughness
• For test piece A=0.7944
• For test piece H=9.5818
2. Artificial defects are made by drilling side holes as sub surface defects.
• Defects are made in subsurface (3 mm) by drilling with different diameter (8mm, 6.5mm, 5mm & 4mm) drill bits.
3. Experiments are conducted in two modes
• 1.Contact test
• 2.Non-contact test(Immersion test)
Contact test is made by placing the probe on the test piece with couplant.
2.Non-contact test(Immersion test):
• Test piece is placed in the couplant tank.
• Testing is done by placing the probe on the top of couplant level.
Placing of probe is important in this method. Probe should be parallel to the couplant level, otherwise the ultrasonic waves will not propagate properly