Effects Of High Temperature And Long-term Immersion On Fatigue Performance Of Unidirectional Pultruded CFRP Plate

Pultruded carbon fiber reinforced polymer(CFRP)plate possess many desirable characteristics such as high strength/weight ratio,superior resistance to fatigue and corrosion,and have been widely applied in structural rehabilitation and strengthening industrial structures.Pultruded CFRP plate is often designed to sustain fatigue load,and is often exposed to harsh environment like moisture absorption or high temperatures in civil engineering applications.High temperatures and long-term immersion can accelerate fatigue degradation of plates,and shorten plates fatigue life.In order to design and application of unidirectional pultruded CFRP plates in the civil engineering structure with economical and safe,the paper tries to study the effect of high temperature and long-term immersion on fatigue behaviors of unidirectional pultruded CFRP plates through fatigue test at high temperature and after exposed to water/alkaline solution respectively.The study found that the effect of high temperature on static performance of pultruded CFRP plate was small,but high temperature had more obviously effect on fatigue performance.The fatigue life under low stress level at high temperature was greatly reduced compared with low temperature,but it had significantly increased under the high stress level.By predicting of S-N curves,when the fatigue lives reach 2 million cycles,limit value of stress are 69.39%,68.80% and 64.89% of the ultimate stress for room temperature,50? and 83?,respectively.And by predicting of the Whitney's method with a reliability of 95%,when the fatigue lives reach 2 million cycles,limit value of stress are 49.95%,49.03% and 43.24% of the ultimate stress for room temperature,50? and 83?,respectively.The effect of static performances and fatigue behaviors after exposure to distilled water for two years of pultruded CFRP plate was small.After exposure to alkaline solution for two years,static performances of the pultruded CFRP plate were slightly decreased,and fatigue behaviors had more significantly influence.Performances of resin and fibre/matrix interface were worsened after exposure to water and alkaline solution for two years,and fibre/matrix interface had more cracks,the matrix had more bigger ripples of CFRP specimens under fatigue loading.Deterioration phenomenon of CFRP plates after exposure to alkaline solution was more serious,and splitting failure of CFRP plates was more likely to occur,causing the stiffness suddenly decreases.The fatigue life can be increased by reducing loading,and reducing the probability of fracturing failure.Thermal analysis show that performance of plates had declined after immersion aging,the performance of resistant to rising temperatures for the resin had a certain decrease,and thermal stability properties of the plate was also reduced.By predicting of S-N curve,when the fatigue lives reach 2 million cycles,limit value of stress are 69.28%,68.72% and 60.75% of the ultimate stress for non-immersed,distilled water immersion and alkaline solution immersion,respectively.And by predicting of the Whitney's method with a reliability of 95%,when the fatigue lives reach 2 million cycles,limit value of stress are 73.39%,72.72% and 68.55% of the ultimate stress for non-immersed,distilled water immersion and alkaline solution immersion,respectively.By predicting of the Sendeckyj's method with a reliability of 95%,when the fatigue lives reach 2 million cycles,limit value of stress are 65.00%,65.93% and 54.41% of the ultimate stress for non-immersed,distilled water immersion and alkaline solution immersion,respectively.