Application of Shear Wave Focused Image Holography to Nondestructive Testing

Abstract

This paper describes a method for sizing vertical and oblique flaws or defects within metal structures be the use of scanned acoustical holographic interferometry in the focused image hologram mode. The image of an internal flaw obtained from focused image holography consists of interference fringes or contour lines across the flaw’s surface. The fringe separation represents half wavelength deviations in depth from the scanning plane and the length of the fringes corresponds to the width of the flaw. Thus, it is possible to evaluate flaw size by measuring the number and length of fringes appearing on the focused image hologram.

The theory developed in the present paper gives the relation between the flaw size and the number and separation of fringes on the hologram. Measurements resulting from the application of the theory, to artificial flaws in metal test pieces are examined in the experiments in this paper. The deviations of the obtained heights from the true values measured by physical means are 10% for the 4.0 mm height flaws at 3.0 MFz 5 % at 5.6 MHz. Natural vertical flaws produced at the electron beam welded interface on a steel test piece are also imaged and the size of flaws is measured by acoustical interferometry.