T.O. 33B-1-1Glossary 73REFERENCE BLOCKS: A block or series of blocks of material containing artificial or actual discontinuities of one ormore reflecting areas at one or more distances from the test surface, which are used for reference in defining the sizeand distance of defective areas in materials.REFERENCE NUMBER: A mathematical value established to summarize the combined effects of conductivity,magnetic permeability, test frequency, coil radius and thickness for use in impedance diagrams.REFERENCE RADIOGRAPHS: A group of radiographs containing images of discontinuities. These can be used ascomparison “standards” for acceptability of materials.REFERENCE STANDARD: A piece of material, part, or piece from a part, containing an artificial discontinuity ofknown size; provides a means of producing a reflection of known characteristics; used to establish a measurement scale.Also, a known size discontinuity used to produce a reflection of known characteristics. References are constructed forthickness measurement, conductivity measurement or flaw detection.REFLECTION (UT): An indication that has arisen as a result of an incident sound beam being reflected at theboundary of two materials of dissimilar acoustic impedance.REFLECTION DENSITY (RT): The common logarithm of the ratio of the brightness of a non-absorbing perfectdiffuser to that of the sample, both being illuminated at an angle of 45 degrees to the surface, the direction ofmeasurement being normal to the surface.REFLECTOGRAM: A picture of recording of the indications presented on the cathode ray tube of the ultrasonicinstrument.REFLECTOGRAPH: A recording or chart made of either the signals transmitted through a part or reflected back fromdefects within a part, or both.REFLECTOR (UT): An interface at which an ultrasonic beam reflects.REFRACTED BEAM (UT): The beam that occurs in the second medium when an ultrasonic beam passes obliquelyfrom one medium to another when each medium has different sound velocities.REFRACTION (UT): Change in direction of an ultrasonic beam as it passes obliquely through the interface betweentwo materials with different acoustic velocity; see SNELL’S LAW.REFRACTIVE INDEX (UT): The ratio of the velocity of a wave in one medium to the velocity of the wave in a secondmedium is the refractive index of the second medium with respect to the first. It is a measure of the amount a wave willbe refracted when it enters the second medium after leaving the first.REFRACTORY:(1)A material of very high melting point with properties that make it suitable for such uses as furnace liningsand kiln construction.(2)The quality of resisting heat.REFRACTORY ALLOY:(1)A heat-resistant alloy.(2)An alloy having an extremely high melting point. See REFRACTORY METAL.(3)An alloy difficult to work at elevated temperatures.
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