Experimental investigation on toughening mechanism in CFRP laminates
Evaluation of interlaminar properties under static and fatigue loading is essential to ensure reliability in structural applications such as primary structures of aircraft. For CFRP laminates with toughened matrices, it is common that the mode I fracture toughness value increases with the crack extension due to fiber bridging. Under fatigue loading, the crack propagation rate decreases with the crack extension by keeping the energy release rate constant. On the other hand, rather constant fracture toughness values are often obtained under mode II fracture toughness tests except for the early stage of the tests. The fatigue crack propagation rates are not influenced by the crack extension. The difference in the fracture mechanisms between mode I and II static fracture was investigated from the view points of microscopic fracture mechanisms using high resolution X-ray computed tomography at the damaged zone near the crack tip. It is clear that the contribution of bridging fiber under mode I is much more than that under mode II. At the early stage the fracture toughness tests under mode II, quick increase of the toughness is observed for toughened laminates when the crack length is determined by the change in compliance. The cause of this early stage behavior will also be discussed.
Masaki Hojo received the B.S., M.S. and Ph. D degrees in engineering science from Kyoto University in 1979, 1981, 1990, respectively. He was researcher of Industrial Products Research Institute, Agency of Industrial Science and Technology (AIST), Ministry of International Trade and Industry (MITI) in 1981, associate professor of Mesoscopic Materials Research Center, Faculty of Engineering, Kyoto University in 1992, and professor of Department of Mechanical Engineering and Science in 2001. His research includes delamination, fatigue and experimental micromechanics of composites and superconducting materials. He was President of the Japan Society for Composite Materials （JSCM） for the period of 2012 to 2014. He was also Vice President of the Society of Materials Science, Japan (JSMS) for the period of 2012 to 2014. He was President of the Asian-Australasian Association for Composite Materials for the period of 2012 to 2014. He is now member of ICCM Executive Council. He is also Chairman of ISO/TC61/SC13 (Composites and Reinforcement Fibers).
He published more than 290 refereed journal papers, 30 review articles, and received 19 awards. He is a Fellow of the Japan Society for Mechanical Engineers (JSME) and the Japan Society for Composite Materials.