MICROSTRUCTURE ANALYSIS OF STEEL 85 & AL-7050 FOR COLD EXPANDED HOLES

Basavaraj, Shanmukh. N

Abstract: Introduction of beneficial compressive residual stresses at fastener hole to retard the cracking in material subjected to fatigue loading. Among various techniques, cold expansion is most oftenly used to achieve the introduction of compressive stresses. The present work investigates the microstructure changes along the radial selling section of holes after the cold working of holes. Two different materials, steel 85 & AL-7050 with thickness 12mm and 6mm were selected for conducting experiment. The split sleeve method was used to expand the holes to different percentage and microstructures are observed using SEM. Micro graphs clearly showed a zone of plastic deformation close to the hole fallowed by a zone of elastic compression induced by the split sleeve expansion. The pattern after different extent of expansion of holes was studied and comparative study of microstructure of holes, before and after expansion was done

Keywords: Residual stresses, cold hole expansion microstructure, split sleeve process, micro graph

DOI: https://doi.org/10.15623/ijret.2014.0315182