GB641461A - Improvements in or relating to supersonic wave method and apparatus - Google Patents

Abstract

641,461. Testing materials by supersonic vibrations. UNITED AIRCRAFT CORPORATION. Feb. 4, 1944, No. 2134. Convention date, Jan. 2, 1943. [Class 118 (ii)] [Also in Group XXXIX] In the interior or surface inspection of an elastic body by means of ultrasonic mechanical waves, the surface of the wave generator in contact with the body executes a combined lateral and angular movement. Fig. 3 shows an end view of a Y-cut quartz crystal which will thus vibrate when placed in an oscillating electric field, and may be used to produce surface or shear waves in material under test. As. applied to tests for rigidity, surface flaws, &c. two such quartz crystals 10, 18, Fig. 7, are interposed between electrodes 16, 20 and the surface of the material 12 under test, which in this case serves as the second electrode for both the emitter and receiver ; the potential produced across the electrodes of the receiver by vibration in response to surface waves generated by the emitter is amplified and applied to an indicator, such as an oscilloscope to which the emitter is also connected. The amount of adjustment necessary to the micrometer 30 between two points at which the phase of the emitted and received waves coincides (as shown by the oscilloscope) gives an indication of the wavelength from which, the frequency being known, the velocity may be calculated and an indication thus obtained of the rigidity of the material about various axes ; the velocity may also be determined by timing the passage of a wave train from the emitter to the receiver, or the reflected time to and from a reflector at a known distance if the emitter is also used as the receiver. Timing in this way at a known velocity may also be used to locate a surface flaw. Observation of the degree of attenuation at varying wavelengths may provide a means for determining the size and extent of inclusions (such as free graphite in cast iron), or as a measure of the roughness of, e.g. a machined metal surface. Separate electrodes may be interposed between the quartz crystals 10, 18 and the material 12, or a YZ face of the crystal or one long edge of a YZ face (the crystal in this case being at an angle) may contact the material, electrodes being placed on the two XZ faces. An oil film may be applied to inhibit the radiation of waves into the body of the material. Specifications 569,858, [Group XL], and 641,095 are referred to.