Simulation and measurement of cryogenic-interfacial-properties of T700/modified epoxy for composite cryotanks

Interface between the carbon fiber and epoxy was vital to the mechanical performance of CFRP under cryogenic temperature (−196 °C). In this paper, the cryogenic-interfacial-properties of carbon fiber/modified epoxy (T700/M-Epoxy) under −196 °C were analyzed by experiment, theoretical analysis and finite simulation method (FEM). Experimental data showed that the interfacial shear strength (IFSS) of T700/M-Epoxy at −196 °C was 75.8 MPa, which was increased by 16.1% in comparison with that (65.3 MPa) under room temperature (RT). For theoretical analysis, the microbond sample could be simplified into a cylindrical model. The increase of IFSS at −196 °C derived from contraction deformation of M-Epoxy. FEM was employed to simulate the distribution of interfacial stress and the evolution of debonding in T700/M-Epoxy. Based on the FEM model, both debonding and friction force (148.2 mN, 40.3 mN) at −196 °C were much higher than those (112.6 mN, 21.3 mN) under RT because of coefficient of thermal expansion (CTE) mismatch between T700 and M-Epoxy. The theoretical analysis and FEM simulation made the experimental findings understood well, and they also could be used to predict the interface stress of fiber/resin at cryogenic temperature.