Characterization of Fiber Pull-Outs in Drilled CFRP Holes Using Confocal Laser Microscope

Carbon Fiber Reinforced Plastic (CFRP) material is often drilled when constructing a large aircraft structure. When drilling CFRP, many defects can be left on the CFRP hole surface. One of the most detrimental surface defects is known as fiber pull-outs, which occur when bundles of fibers are pulled away by fiber-matrix de-bonding and matrix stripping. The objective of this research is to use confocal laser scanning microscope (CLSM) in order to characterize fiber pull-outs occurred during the drilling process of quasi-isotropic CFRP. This new optical characterization method is capable of measuring maximum depth and the distributions of fiber pull-outs. Fiber pull-outs are also qualitatively characterized by SEM and CLSM. It is found that the average depth of fiber pull-outs acquired from CLSM is approximately two times larger than those from the surface profilometer. However, there is a proportional correlation of the data between CLSM and surface profilometer.