Unidirectional carbon fiber reinforced epoxy (CFs/EP) laminate was prepared by vacuum bag molding process. By the combination of high-low temperature test box and universal testing machine, and rational use of low temperature adhesive and low temperature extensometer, cryogenic (liquid oxygen temperature, -183℃) tensile and flexural tests were conducted. During the cooling process, the stress and strain were set to zero timely. According to the microscopic and macroscopic characteristics of samples, the cryogenic mechanical properties change mechanisms of unidirectional CFs/EP laminate were revealed. The results show that, compared with the mechanical properties at room temperature, the cryogenic tensile strength of unidirectional CFs/EP laminates decreases about 9.5%, while the tensile modulus increases by about 6.2%. It is mainly due to that the resin shrinkage between carbon fibers and resin forms a strong interface at low temperature. The "split" failure mode forms in the cryogenic tensile specimen, which means that not every fiber of unidirectional CFs/EP laminate develop its full strength, and leads to the tensile strength decreasing. While the low temperature limits resin molecular chain movement, which results in the tensile modulus of unidirectional CFs/EP laminates increasing. The cryogenic flexural strength and flexural modulus of CFs/EP laminates are increased to about 54.75% and 11.64%, respectively. It is because the bending failure mode of unidirectional CFs/EP laminates at room temperature and low temperature both are delamination shear failure. The cryogenic strong interface of unidirectional CFs/EP laminates improves interlamination shear resistance and makes the cryogenic flexural properties of unidirectional CFs/EP laminates improved.
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