Fabrication of photoresist diffraction gratings on Ti-6AI-4V beam specimens for use in moire interferometry

Photoresist diffraction gratings of 1200 lines mm(-1) were produced directl y on Ti-6Al-4V beam specimens to study fatigue crack closure using moire in terferometry. A dyed photoresist was used to overcome the problems of refle ction causing standing waves in the photoresist. Dipping was the best metho d of applying an even layer of photoresist to the specimen. The specimens w ere manufactured oversize, then machined to size after the gratings had bee n produced, to remove the bead at the specimen edge. This paper outlines th e processes required to produce the photoresist gratings and a brief descri ption of the combined moire interferometer and fatigue rig used.