Study of fiber pull-out characterization in drilling carbon fiber reinforced polymers

The demand for carbon fiber reinforced polymers (CFRP) in aerospace industries has increasingly risen over the past years. CFRP composites are often mechanically joined to the structures or other metals using bolts and rivets. Acquiring high quality holes is essential to manufacturing process in order to get precise and damage-free holes and facilitate assembly procedure without rework. Fiber pull-outs are one of most common hole surface damages when drilling CFRP plates, which have not been analyzed extensively.  This study aims to investigate the effects of cutting conditions and tool geometry on fiber pull-out occurrence when drilling CFRP. The experimental trails carried out using three drill geometries at different machining conditions (feed and speed combination) on a quasi-isotropic CFRP plate. The fiber pull-out area and depth were quantified with respect to the interaction angle of the tool and fiber directions (tool-fiber angle). The results revealed that the fiber pull-outs occurred at the regions with specific tool-fiber angles (160 to 135 degrees). Results also revealed that tools with lower rake angle produce deeper fiber pull outs with less damaged surface area on hole wall. The results allow customization of the machining processes to minimize, predict and avoid the occurrence of fiber pull out in drilling composites.