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Full-Text Articles in Aerospace Engineering
Generation Of Horizontally Polarized Shear Waves In Ferromagnetic Materials Using Magnetostrictively Coupled Meander‐Coil Electromagnetic Transducers, R. Bruce Thompson
Generation Of Horizontally Polarized Shear Waves In Ferromagnetic Materials Using Magnetostrictively Coupled Meander‐Coil Electromagnetic Transducers, R. Bruce Thompson
R. Bruce Thompson
A new electromagnetic transducer configuration is described for generating horizontally polarized shear (SH) waves in ferromagnetic materials. The transducer consists of a meander coil and static bias magnetic field parallel to the coil elements. This configuration generates no ultrasonic waves in a nonmagnetic metal since the induced eddy currents are parallel to the bias field and the driving Lorentz forces vanish. However, the configuration provides coupling to SH waves in ferromagnetic materials through magnetostrictive effects. Experimental measurements of the variation of transduction efficiency with bias field in nickel and 4130 steel plate are presented and compared to the efficiency obtained …
An Elastic‐Wave Ellipsometer For Measurement Of Material Property Variations, R. Bruce Thompson
An Elastic‐Wave Ellipsometer For Measurement Of Material Property Variations, R. Bruce Thompson
R. Bruce Thompson
Electromagnetic‐acoustic transducers (EMAT’s) can excite and detect elastic shear waves with electronically controlled elliptical polarizations. These can be used to construct an ellipsometer for precise measurement of mechanical properties of solids, in analogy to devices presently used in optical studies. The elastic‐wave case differs from the optical case in two important ways. Longitudinal as well as transverse waves will, in general, exist, and the propagation medium, as well as the surfaces, play an important role in determining the system response. A device is described which is designed to avoid the former mode conversion effects on thin plates. The results of …
Strain Dependence Of Electromagnetic Generation Of Ultrasonic Surface Waves In Ferrous Metals, R. Bruce Thompson
Strain Dependence Of Electromagnetic Generation Of Ultrasonic Surface Waves In Ferrous Metals, R. Bruce Thompson
R. Bruce Thompson
It is demonstrated that the efficiency of the electromagnetic generation of ultrasonic surface waves in ferrous metals is strongly influenced by superimposed elastic strains. A graph of efficiency versus applied magnetic field has many features, and the changes of these in Armco iron and 1018 Steel are reported for the strain range −3×10−3 <Δl/l <3×10−3 (‖calculated stress‖<620 MN/m2 or 90 KSI). Striking changes are observed, particularly for fields below 200 Oe. The results are interpreted in terms of the strain dependence of the magnetostrictive properties of the material. Possible applications of the effect to nondestructively measure residual stress are considered.