THERMOELECTRIC NONDESTRUCTIVE CHARACTERIZATION OF SUBSURFACE INCLUSIONS

摘要

A comparison between published analytical results with experimental ones of the magnetic field produced by thermoelectric currents of subsurface semi-spherical pure tin inclusions embedded in a copper bar under the influence of an external heating (+45℃) and cooling (+10℃) into the specimen is presented. The measurements were taken from a 12.7 mm-thick copper bar with several subsurface semi-spherical pure tin inclusion diameters at different lift-off distances. The experimental magnetic flux density measurements show a good agreement with analytical ones as a function of the lift-off distances with the different inclusion diameters with the exception of the intrinsic material background magnetic signal that affected deeply the detectability of subtle imperfections in noncontacting thermoelectric measurements. The main sources of such adverse background signals in thermoelectric NDE are the intrinsic variations of the material properties of the specimen to be inspected.