Why use ultrasonics for nondestructive material testing?
At the beginning of the fifties the technician only knew radiography (x-ray or radioactive isotopes) as a method for detection of internal flaws in addition to the methods for nondestructive testing of material surfaces, e.g. the dye penetrant and magnetic particle method. After the Second World War the ultrasonic method, as described by Sokolov in 1935 and applied by Firestone in 1940, was further developed so that very soon instruments were available for ultrasonic testing of materials. The ultrasonic principle is based on the fact that solid materials are good conductors of sound waves. Whereby the waves are not only reflected at the interfaces but also by internal flaws (material separations, inclusions etc.). The interaction effect of sound waves with the material is stronger the smaller the wave length, this means the higher the frequency of the wave. λ=c/f • c = Sound velocity [km/s] • f = Frequency [MHz] • λ = Wave lenght [mm] This means that ultrasonic waves must be used in a
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