A MODEL-FITTING APPROACH TO THE BROAD-BAND MEASUREMENT OF ULTRASONIC WAVE VELOCITIES IN THIN SAMPLES OF ENGINEERING MATERIAL

This paper presents a novel broad band short-pulse ultrasonic system f or the simultaneous measurement of compression and shear acoustic wave velocities in thin solid slabs. Using a goniometer stage a test sampl e is immersed in a water cell between two axially aligned thick ultras onic transducers. Compression and shear wave reverberations are genera ted in the test material and the resulting compression waves in the wa ter on the receiver side are received and digitized. Each wave reverbe ration can be separately time resolved and time-of-flight (TOF) measur ements can be made. A time domain model of the wave system in the soli d is presented with comparisons with existing frequency domain models. The measured arrival times of the successive reverberations are input to a computer algorithm derived from the time domain model which, usi ng a parameter fitting routine, calculates the acoustic wave velocity for both the compression and shear reverberations in the sample. The p roblem of interference between successive reverberations in the time d omain is greatly reduced due to the wide bandwidth/short pulse operati ng mode possible with acoustically thick transducers.