Influences of long-term immersion of water and alkaline solution on the fatigue performances of unidirectional pultruded CFRP plate

Moisture absorption rate (M t ), static tensile strength (f u ), fatigue life (N), stiffness degradation curves of unidirectional pultruded CFRP plates during two years distilled water (DW), alkaline solution (AS), and non-immersion (NI) were comprehensively studied along with their thermal behavior, microstructure and fatigue failure mechanism; Their stress level (S)-N curves were further fitted and predicted by three methods. Results reveal, the N of the pultruded CFRP plate with AS is much lower than those with DW and NI. The corresponding microstructure deteriorations with AS are more serious, and the resin ripples under higher S and AS are much more and bigger than with DW and NI. When the N reaches 2 million, the allowable S in S-N prediction curves is 69.28%f u , 68.72%f u and 60.75%f u with NI, DW and AS for 2 years, respectively. The corresponding allowable S in Whitney's method and Sendeckyj's method with a reliability of 95% is 73.39%f u , 72.72%f u , 68.55%f u and 65.00%f u , 65.93%f u , 54.41%f u , respectively.