George A. Alers

Ultrasonic inspection of pipelines

A method and device which are suitable for the in-place inspection of pipelines are provided. A completely self-contained, mobile inspection station is placed inside a pipeline. The station runs through the pipe and transmits Lamb waves within the pipe wall, receives reflected and transmitted portions of the waves, and records the amplitude and phase of the received waves. The recorded information is analyzed to determine the location and nature of discontinuities in the pipe.

Dispersion of flexural elastic waves in honeycomb sandwich panels

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...

Lamb wave measurements for rapid monitoring of sheet metal

Lamb waves represent a very natural choice of interrogating energy for problems involving ultrasonic inspection of sheet and plate shaped materials. They have not enjoyed wide use in nondestructive evaluation because their excitation and detection by piezoelectric transducers require special mechanical supports and corrections for the acoustic loading of the sheet by the coupling medium must be made. By using properly designed electromagnetic acoustic transducers (EMATs), the transducer supports can be simplified, corrections for leaky waves can be eliminated, and very specific modes can be used to optimize a particular inspection process. Several examples of using special Lamb wave modes to inspect pipes and tubes in industrial environments will be presented, and their use for materials characterization in ferromagnetic metals will be emphasized.