A 50 MHZ SURFACE WAVE SCATTEROMETER FOR THE EVALUATION OF MACHINED CERAMIC SURFACES

CERAMIC MACHINING GENERATES SUBSURFACE CRACKS THAT CA GROW AND LEAD TO THE FRACTURE OF MACHINED PARTS. IT IS THUS IMPORTANT TO MEASURE THE DAMAGE DUE TO MACHINING. SUCH A MEASUREMENT COULD BE USED TO IMPROVE MACHINING METHODS, AND FOR EHT NONDESTRUCTIVE EVALUATION OF MACHINED PARTS. THE TECHNIQUE WE PROPOSE IS BASED ON USING SCATTERED ULTRASONIC SURFACE WAVES TO MEASURE THE SIZE AND DISTRACTION OF MICRO-CRACKS ASSOCIATED WITH MACHINING DAMAGE OF CERAMIC SURFACES. VERY SIMPLY, WE WILL USE SURFACE WAVE TRANSDUCERS FOR OPERATION IN THE 25-50 MHZ FREQUENCY RANGE AND MEASURE THE AVERAGE BACK SCATTERED SURFACE WAVE SIGNAL AS A FUNCTION OF DISTANCE AWAY FROM THE TRANSDUCER. THE MEASUREMENT IS MADE IN A BROAD BAND (PULSED) MODE. THE RECEIVED SIGNAL IS DIGITIZED AND STORED, THE TRANSDUCER IS MOVED SLIGHTLY AND A NEW SIGNAL IS CAPTURED AND ADDED TO THE PREVIOUS SIGNAL. THIS PROCESS IS REPEATED A NUMBER OF TIMES AND AN EXPONENTIAL DECAY OF THE SURFACE WAVE IS MEASURED AS A FUNCTION OF DISTRIBUTION OF SURFACE MICRO-CRACKS. OUR OVERALL GOAL IS TO DEVELOP A FAST, SIMPLE, EFFICIENT AND INEXPENSIVE COMMERCIAL TOOL FOR THE INSPECTION OF MACHINING DAMAGE.