COBEM99

S24 Mecânica dos Sólidos

Title:

SURFACE STRESS MEASUREMENT USING LONGITUDINAL CRITICALLY REFRACTED (LCR)WAVES

Summary :

ABSTRACT. LONGITUDINAL WAVES GENERATED BY ULTRASONIC PROBE TRAVEL IN THE SURFACE OF THE MATERIAL WHEN THE ANGLE OF INCIDENCE IS APPROXIMATELY EQUAL TO THE FIRST CRITICAL ANGLE. FOR STEEL WITH A PLEXIGLAS WEDGE, THIS ANGLE IS 28O. A LONGITUDINAL WAVE TRAVELING IN THE DIRECTION OF THE STRESS FIELD IS THE ONE MOST SENSITIVE TO STRESS VARIATIONS. THIS WORK SHOWS THE DETERMINATION OF STRESSES IN THE SURFACE OF PLATES USING LCR WAVES. AN ESTIMATE OF MAGNITUDE OF THE STRESSES WAS DETERMINED BY THE FINITE ELEMENT METHOD. THE PROBE IS BUILT IN A RIGID STRUCTURE AND COMPRISED OF TWO SENSORS MOUNTED IN A PLEXIGLAS SUPPORT AND POSTED AT A FIXED DISTANCE ONE FROM EACH OTHER. THE ELECTRONIC SYSTEM IS ABLE TO SAMPLE AT 100 MHZ AND THE INTERPOLATION OF THE RESULT PERMITS THE STANDARD DEVIATION FOR TRAVEL TIME IN EACH MEASURE TO BE LOWER THAN 3 NANOSECONDS. THE COMPARISON BETWEEN THE THEORETIC AND EXPERIMENTAL RESULTS SHOWS THAT IT IS POSSIBLE TO IDENTIFY THE TENSILE AND COMPRESSIVE REGIONS INSIDE THE PLATES USING THIS SYSTEM, AND TO CALCULATE THE MAGNITUDES. FURTHER DEVELOPMENTS OF THE METHOD PROVIDE A VALUABLE NONDESTRUCTIVE WAY TO EVALUATE STRESSES IN MECHANICAL COMPONENTS. KEYWORDS: ULTRASONIC TECHNIQUES, NONDESTRUCTIVE STRESS MEASUREMENTS, LONGITUDINAL WAVES.

Author :

Bray, Don E.
Kypa, Jagan M. R.
Santos, Auteliano Antunes

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