Detection of the surface defects in thin polymeric films using projection moiré

Abstract

Experimental investigations of the polymeric films HDPE and PP and of the multi-layered material PET+LDPE with defects (puckered surfaces, holes and segregation of the upper layer) were performed. For this purpose, the method of projection moiré was used. In the process of investigations, the images of the defects were determined. During the experimental investigations it was determined that the images and shapes of the eigenmodes, as well as the frequencies and amplitudes of vibrations change due to mechanical or structural defects in the polymeric films and because of symmetrical or un-symmetrical loading. Typical optical images for various types of defects were determined. In the paper smoothness of fringes by using the method of time averaged geometric moiré is also investigated. On the basis of a one dimensional model graphical relationships for linear variation with respect to longitudinal coordinate of amplitude of vibrations are obtained. They provide the background for the choice of the required number of images in a period of oscillations for different smoothnesses of moiré fringes.