The elements of the concrete structure are most frequently affected by cracking. Crack detection is essential to ensure safety and performance during its service life. Cracks do not have a regular shape, in order to achieve the exact dimensions of the crack; the general mathematical formulae are by no means applicable. The authors have proposed a new method which aims to measure the crack dimen...

A new method for elliptical shape detection based on the principle of gray and mass moment preserving is proposed. For each elliptical region in a gray-scale image, automatic bilevel thresholding based on gray moment preserving is used first to transform the blurred image in the region into a binary picture. The five parameters of the elliptical shape are then computed using the mass moment pre...

The diffraction of SH waves by a finite plane crack is studied. The classical Sommerfeld solution for a semi-infinite straight reflecting screen is used as a building block to calculate the diffracted field generated by a finite crack. The solution is derived from the analysis of the behaviour of diffracted waves. These waves, which are first generated at the edges of the crack, travel along th...

This paper explores theoretically the possibility of using caustics, formed in the ultrasonic field diffracted by defects, as an approach to the inverse scattering problem, The case of crack-like defects is considered in detail, using the geometrical theory of diffraction. The involute of the far field caustic reproduces the projection of the crack edge in the incident beam direction, for a pla...

We have considered a semi-infinite crack embedded in a transversely isotropic medium and studied two special cases, one, in which the axis of symmetry is normal to the crack face and the wave incidence is arbitrary and another, in which the axis lies in the crack plane normal to the edge and the incident wave vector is also normal to the edge. The problem is of interest in Non-Destructive Evalu...