It is well established that elastic waves may be generated in a metal without physical contact through the reaction of a static magnetic field and dynamically induced eddy currents. The technique can significantly reduce the time needed in certain ultrasonic inspection problems because there is no need to re-establish a mechanical bond at each point of measurement. However, it has not yet received sufficient attention to determine its potential in actual industrial problems. This paper describes a feasibility study of the application of direct electromagnetic transduction to the inspection of gas pipelines from within the pipe. Experimental results are presented demonstrating the generation and detection of 130 kHz antisymmetric Lamb waves in 3/8 in. thick steel plate and pipe. The sensitivity of the process to various design parameters is discussed as well as the amplitude of signals reflected from defects. The experimental results for transduction and reception efficiencies are compared to a theoretical model.
Ultrasonic measurements which were designed to test the theory of reflections of harmonics generated by finite amplitude waves at stress free boundaries in solids have been made. The results are found to be in agreement with theoretical expectations.
The phase velocity of flexural waves traveling along a 1-in.-thick honeycomb sandwich panel has been experimentally determined from 170 Hz to 50 kHz by using three techniques: measurement of resonant frequencies of beam-shaped samples in forced vibration, measurement of nodal spacing in standing wave patterns on beam-shaped samples, and measurement of the change in time delay of a particular phase feature of a wave packet as a function of propagation distance on large plate samples. The experimentally determined velocities ranged between 2.2×104 cm/sec at 170 Hz to 1.18×105 cm/sec at 40 kHz. This dispersion arises primarily from the geometrical effect of the finite thickness of the panel and agrees well with two theoretical models; a plate theory and an elasticity theory, each of which treats the core as a continuum. Above 40 kHz, the predictions of the two models differ greatly for the particular panel geometry studied. The experimental phenomena become more complex and appear to agree with neither model, quite possibly due to the neglect of the periodicity of the core. A brief description of these results is given.
Subject Classification: 40.24; 35.26.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.