Effect of interlaminar and intralaminar structure on fracture of high strength CFRP and optimization of mesoscopic structure

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Effects of interlaminar and intralaminar mesoscopic structures on the fracture toughness and fatigue crack growth resistance were investigated for CFRP laminates. In the present study, resin layrs at the prepreg interfaces and fiber/matrix interfacial strength were controlled. Comparison of interlaminar and intralaminar fracture properties was carried out to find out the role of resin rich layrs at the prepreg interface. A new type of heterogeneous resin for resin rich layrs which is composed of thermoplastic fine particles and epoxy of base lamina was also investigated. Finally, the effect of thickness and toughness of the resin rich layrs at the prepreg interface was separately analyzed, and the optimization of the resin rich layrs was discussed. The results are summarized as follows :1.Mode II interlaminar properties of CFRP laminates with heterogeneous resin at prepreg interfaceFracture toughness and fatigue crack growth resistance were improved up to the level of CFRP laminates wi … More th tough thermoplastic resin. This high toughness was kept with the increment of crack growth.2.Mode I and II interlaminar properties of thermoplastic resin interleaved CFRPPolyethylene base thermoplastic resin was put at the prepreg interface of CFRP laminates. The mode I fracture toughness was almost the same as that for CFRP laminates with thermoplastic resin matrix. This high toughness was kept with the increment of crack growth. For the case of mode II,the toughness was more than 10kJ/m^2, which was much higher than that for CFRP laminates with thermoplastic resin matrix.3.Effect of fiber/matrix interfacial strength on interlaminar and intralaminar fracture propertiesThe fracture toughness for mode I intralaminar tests increased with increasing surface treatment levels. The effect of the surface treatment on the fracture toughness for mode II interlaminar tests was smaller than that for mode I intralaminar tests. The fracture toughness for mode I interlaminar tests was insensitive to the surface treatment level for CF/epoxy laminates. The mesoscopic fracture mechanism was well correlated to the effect of the surface treatment on the basis of SEM observation. Less