Application of subsurface laser engraving in ultrasonic testing of materials

摘要

Various samples with artificial flaws found application in ultrasonic testing of materials. Some of them are used for education, some for calibration of ultrasonic equipment. Possibility of manufacturing of various reflectors in metal blocks are usually limited to simple geometries like cylinders, flat bottom holes, various grooves or notches. There are also limitations to produce small reflectors deep under the surface. All reflectors manufactured using machining present 100% reflectivity of ultrasonic waves. Alternative to steel samples with machined reflectors is optical glass and subsurface laser engraving. Velocities of longitudinal and shear ultrasonic waves in optical glass are almost the same as in carbon steel. Laser engraving allows to produce inside the glass block almost unlimited variety of reflector shapes, orientations and sizes. Single laser action produces a small, about 0,1 mm long, cracking. Such cracks, situated close to each other, can create various surfaces. Separated cracks spread in the volume can modify acoustic properties of naturally isotropic glass and develop acoustic anisotropy, acoustic noise or locally increase attenuation of ultrasonic waves. Paper presents results of measurements performed on laser engraved samples imitating numerous micro-cracks as in steel subjected to creep, regions presenting high acoustic noise and on various artificial flaws reflecting ultrasonic waves.