STUDY ON THE EVALUATION METHOD OF HTE FRACTURE TOUGHNESS OF CFRP LAMINATES.

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The method to evlauate the fracture toughness of CFRP laminates is studied. in this research. The linear fracture mechanics can be used with good accuracy to predict the stress field At the crack tip of CFRP specimen. Then the some numerical methods, for example, finite element method and boundary element method, are available in this study. At first, the fracture experiment and numerical analysis are carried out and the mode I fracture toughness, GIC, is estimated. A new method combining the experiment and analysis is proposed. By this method, it is not necessary to measure the crack length during the experiment. Second, a method to evaluate the fracture toughness of mode II is proposed. In this method, it is necessary to estimate the contact area between upper and lower crack surfaces and the contact force distributions between them. A new BEM code is made for this purpose, and it enables to estimate the contact area and force distributions with good accuracy. By introducing this method in the estimation scheme, the fracture toughness of mode II can be estimated easily. Finally the mixed mode specimen is proposed in this research and the state of mixed mode is checked by the three dimensional finite element analysis. Three dimensional J integral is evaluated and it is decomposed into three modes of stress intensity factors, KI, KII, and KIII. It is shown that though mixed mode fracture occurred in this type of specimen, the fracture mode is mode I dominant. It is concluded that another method to include mode I, II and III should be considered. This problem no attracts a wide attention and a new project between Japan, United States, and Europe is being planned. I will continue to effort to establish a new method to estimate the mixed mode fracture toughness of CFRP laminates as a member of this new project.