EMUS-systems for stress and texture evaluation by ultrasound
Methods for the evaluation of stress and texture by time-of-flight measurements of ultrasonic waves use of a broad variety of wave types, which include normally incident shear waves and compressional waves, Rayleigh waves, Lamb modes and SH modes. Under field condition, the only means for the excitation of normally incident shear waves and SH modes is to use an electromagnetic-ultrasonic (EMUS) system. Apart from this such a type of ultrasonic system provides a high degree of reproducibility and allows high scanning speeds. These features have led to the development of several EMUS probes for applications to time-of-flight measurements and of transmit/receive-electronics with a high power solid-state transmitter stage. The probes include a small permanent magnet probe for linearly polarized shear waves, a transducer with a water-cooled electromagnet for the simultaneous exictation of orthogonally polarized shear in turbine axles, and a combined piezoelectric/EMUS probe for the simultan eous excitation of compressional waves and shear waves in screws also at elevated temperatures up to 150 degree C. EMUS transducers for Lamb and SH modes in plates have also been applied to time-of-flight measurements aiming at texture evaluation. The different probes will be described, and their performance including the electronical system will be discussed. All probes provide good accuracy for the time-of-flight measurements (up to 3 x 10 high minus 5).