MEASUREMENT OF HARDNESS ON ARMOR PLATE BY A COMBINED ULTRASONIC MAGNETIC PROBE

SINCE THE HARDNESS OF ARMOR PLATE IS ACHIEVED BY CAREFULLY CONTROLLED HEAT TREATMENTS THAT MODIFY BOTH THE CHEMISTRY AND MICROSTRUCTURE OF THE SURFACE LAYER, ANY PROCEDURE USED TO QUICKLY MONITOR THE LEVEL OF HARDNESS MUST SIMULTANEOUSLY MEASURE THE CHEMICAL COMPOSITION, THE MICROSTRUCTURE AS WELL AS THE STATE OF RESIDUAL STRESS IN THE SURFACE AND THEN COMBINE THESE PROPERTIES INTO A UNIQUE PREDICTION OF THE HARDNESS VALUE. IT IS PROPOSED HERE TO PROVIDE A SINGLE HANDHELD PROBE THAT CAN MAKE CRITICAL ULTRASONIC AND MAGNETIC MEASUREMENTS ON A SMALL AREA OF THE SURFACE AND USE THE DATA THUS OBTAINED TO UNIQUELY DEFINE THE HARDNESS. THE DESIGN OF THE PROBE USES ELECTROMAGNETIC ACOUSTIC TRANSDUCERS (EMATS) TO EXCITE AND DETECT RAYLEIGH AND SH WAVES FOR MEASURING THE STRESS AND TEXTURE OF A THIN SURFACE LAYER. IN ADDITION, THE PULSED ELECTROMAGNET USED BY THE EMATS WILL BE USED TO GENERATE BARKHAUSEN NOISE FROM WHICH THE DEFECT STRUCTURE OF THE SURFACE CAN BE INFERRED. MEASUREMENTS OF THE MAGNETIC PROPERTIES OF THE SURFACE WILL ALSO BE MADE BY USING THE TIME DEPENDENT FIELDS UNDER THE EMAT PULSED MAGNET. OUT OF THESE MEASUREMENTS, AT LEAST FIVE INDEPENDENT PHYSICAL PROPERTIES OF AN AREA OF THE SURFACE UNDER THE PROBE CAN BE DETERMINED. BY MANIPULATING THESE QUANTITIES WITH A COMPUTER, A UNIQUE VALUE FOR THE HARDNESS OF THE SURFACE LAYER WILL BE PREDICTED.