The purpose of this study is to investigate the effect of the addition of sub-micron glass fiber (sGF) into the matrix of carbon fiber reinforced plastics (CFRP) on the impact energy absorption and Compres- sive after impact (CAI) strength of it. The unidirectional (UD)-CFRP was fabricated with UD-carbon fiber fabric and thermoset epoxy resin modified by adding 0.3wt% of sGF. For comparison, UD-CFRP made with the neat epoxy resin was also prepared. The impact energy absorption under out-of-plane impact was measured by using falling-type impact testing equipment. In this study, the applied impact energy was 3, 5, 7, 10, and 20 J by changing the mass of the drop weight. After the tests, a compressive load was also applied to the specimen to investigate the CAI strength of UD-CFRP. Test results showed that when the applied impact energy was relatively low (3 and 5 J), the energy absorption of the modified UD-CFRP was slightly improved, compared to that of the neat UD-CFRP. The projection areas of internal damages of UD-CFRP after the drop weight test were also decreased by the sGF addition. However, when the applied impact energy exceeds 7 J, there were no differences in the energy absorption of UD-CFRP even if the sGF was added to the matrix. The scanning electron microscope (SEM) observations of the fractured surface of UD-CFRP after the drop weight test suggested that the adhesion between carbon fiber and matrix resin was improved by the addition of sGF when the low impact energy was applied. The interlaminar shear strength of the modified UD-CFRP was also improved. The CAI strength of modified UD-CFRP was improved when the applied impact energy was relatively low. However, when the applied impact energy exceeds 7 J, the CAI strength of UD-CFRP was degraded by adding sGF. Therefore, when low impact loading was applied, the addition of sGF into UD-CFRP was effective to improve CAI strength.
CAI test, CFRP, drop weight test, interlaminar shear test, split Hopkinson pressure bar method, sub-micron glass fiber.
 Abena, A., Soo, S.L. & Essa, K., Modelling the orthogonal cutting of UD-CFRP composites.Development of a novel cohesive zone model. Composite Structures, 168, pp.65–83, 2017.
 Imamura, T. & Yamaguchi, Y., Progress of composite material for aircraft structure.Journal of the Japan Society for Aeronautical and Space Sciences, 43(495), pp. 213–223, 1995.
 Noziri, K., Properties required for the design of FRP for aircraft. Materia Japan, 39(11),pp. 897–900, 2000.
 Yang, B., Chen, Y., Lee, J., Fu, K. & Li, Y., In-plane compression response of wovenCFRP composite after low-velocity impact: Modelling and experiment. Thin-WalledStructures, 158, p. 107186, 2021.
 Iwahori, Y. & Ishikawa, T., Impact damage evaluation of interlaminar strength improvedCFRP laminates. The Japan Society of Mechanical Engineers, 305(4), pp. 185–186,2004.
 Ferrier, E., Rabinovitch, O. & Michel, L., Mechanical behavior of concrete-resin/adhesive-FRP structural assemblies under low and high temperatures. Construction andBuilding Materials, 127, pp. 1017–1028, 2016.
 Liu, B., Gao, N., Cao, S., Ye, F., Liu, Y., Zhang, Y., Cheng, L. & Kikuchi, M., Interlaminartoughening of unidirectional CFRP with multilayers graphene and MWCNTs formode II fracture. Composite Structures, 236, p. 111888, 2020.
 Yokozeki, T., Aoki, Y. & Ogasawara, T., Damage behaviors and compressive strengthof toughened CFRP laminates with thin piles subjected to transverse impact loadings.Journal of the Japan Society for Aeronautical and Space Sciences, Japan, 55(643), pp.388–395, 2007.
 Yamada, K., Nishikawa, M., Kotter, B., Matsuda, N., Kawabe, K., Fiedler, B. & Hojo,M., Effect of ply-level hybridization and insertion of metal layers on impact damagemodes and compression strength after impact of thin-ply composite laminates. TheJapan Society for Composite Materials, 46(3), pp. 104–114, 2020.
 Saravanakumar, K., Arumugam, V., Souhith, R. & Santulli, C., Influence of milled glassfiber fillers on mode I & mode II interlaminar fracture toughness on epoxy resin forrabrication of glass/epoxy composites. Fibres, 8(6), p. 36, 2020.
 Kimpara, I., Kageyama, K., Suzuki, T. & Ohsawa, I., Simplified and unified approach tocharacterization of compressive residual strength of impact-damaged CFRP laminates.Key Engineering Materials, 141–143, pp. 19–34, 1998.