An ultrasonic velocity measurement system for verifying material properties

Virtual programming methods were used to develop signal processing algorithms that can efficiently obtain precision time measurements from digitized ultrasonic signals. These algorithms are precision-wise improvements over the traditional "cursor-to-cursor" time measurements frequently used with the majority of today's digital storage oscilloscopes (DSOs). Each algorithm uses a different technique or a variation of a similar technique for ascertaining the transit time of an ultrasonic pulse. Once the transit time is obtained, it is mathematically combined with the material thickness (or the equivalent sound path distance) to acquire either the longitudinal or shear ultrasonic velocity. Precision ultrasonic velocity measurements have been shown to be sensitive to the microstructural variations that exist within materials (variations that occur as result of material type and metallurgical processing) [1,2]. In many cases, ultrasonic velocity measurements can also be correlated to a specific mechanical property (i.e. yield strength, tensile strength, elongation, etc...). Accordingly, any improvements achieved in the precision or resolution of the ultrasonic time measurement directly ameliorates the ultrasonic velocity measurement, resulting in a more proficient method for (ultrasonically) verifying a material's mechanical properties. This thesis describes the implementation and testing of a combination cross-correlation, analytic signal technique. Experimental results have shown that this technique provides the best combination of precision and resolution of the algorithms tested. By incorporating this algorithm into a computer system with the appropriate peripheral equipment (DSO, ultrasonic transducer, and pulser/receiver unit), a system capable of nondestructively (ultrasonically) verifying mechanical properties can be constructed. These types of systems can also, with the appropriate modifications, be implemented as "in-process" type measurements.