An interferometric study of a metal surface under distortion and impact

Abstract

The conditions of use of interference fringes for topographical measurement of metal surfaces are investigated. The optimum conditions of the factors which are involved in the formation of fringe systems in reflexion and which control the sharpness and contrast of the fringes are determined. The limits of resolution of the interference method are discussed with relation to the scale of the surface deformation structures of typical metal crystals. The mechanical twinning of suitably shaped single crystals of Bi, Sb and Sn is investigated and the interferometric measurements of the macroscopic shear of the specimens allows a full determination of the twinning elements involved. These goniometric measurements are pursued to the microscopic scale and thus attention is drawn to the shape of the initial region of twinning and its development; the observations being interpreted against the background of the elastic anisotropy of the metal crystals measurements are made upon the phenomenon of slip by way of the slip bands produced on crystals of Aluminium subject to shearing stress up to 1 kgm.mm-2. The commencement of the translation involved in the formation of surface steps is found to be very rapid but the bands subsequently developed by a more gradual process accompanied by movement of the lamellae between active slip bands; the small angles of tilt involved being measured by means of fringes. The measurements in conjunction with a dislocation model of slip yield quantitative data.