Freeze-thaw resistance of unidirectional-fiber-reinforced epoxy composites

The freeze-thaw resistance of unidirectional glass-, carbon-, and basalt-fiber-reinforced polymer (GFRPs, CFRPs, and BFRPs, respectively) epoxy wet layups was investigated from -30 to 30°C in dry air. Embedded optic-fiber Bragg grating sensors were applied to monitor the variation of the internal strain during the freeze-thaw cycles, with which the coefficient of thermal expansion (CTE) was estimated. With the CTE values, the stresses developed in the matrix of the FRPs were calculated, and CFRPs were slightly higher than in the BFRP and GFRP cases. The freeze-thaw cycle showed a negligible effect on the tensile properties of both GFRP and BFRP but exhibited an adverse effect on CFRP, causing a reduction of 16% in the strength and 18% in the modulus after 90 freeze-thaw cycles. The susceptibility of the bonding between the carbon fibers and epoxy to the freeze-thaw cycles was assigned to the deterioration of CFRP.