Effects Of Hygrothermal Aging On The Tensile Fatigue Behaviors Of Carbon Fiber Reinforced Epoxy Plates

Carbon fiber reinforced polymer(CFRP)composites are widely used in civil engineering structures due to lightweight,high strength,corrosion resistance,ease of processing,etc.As same as other materials in civil engineering,CFRP is applicable to specific environmental conditions and influenced most seriously by hygrothermal aging.In addition,the CFRP structures are worked under complicate alternating load which impaired the performance of CFRP.But there was not a relatively accurate evaluating method for the influence of hygrothermal aging on the tensile fatigue performance of CFRP,which limited the application of the CFRPs in civil engineering structures.In this paper,acceleration test is used to study the long-term durability of unidirectional carbon fiber reinforced epoxy(CFRP)wet lay-ups soaked in distilled water and the effect of hygrothermal aging on the tensile fatigue of CFRP.The content concludes: 1)the variations of water absorption,tensile strength,tensile modulus as well as thermodynamic performance of CFRP plates at 20 °C,40 °C and 60 °C distilled water with soaking time were investigated;2)the fatigue performance of untreated CFRP plates with different stress level,fatigue life prediction by several models based on S-N curves and the damage mechanism of tensile fatigue of CFRP plates were investigated;3)the fatigue performance of CFRP plates immersed in 20 °C,40 °C and 60 °C distilled water in the same stress level with immersing time and the mechanism of hygrothermal aging on tensile fatigue by SEM photos and micrographs were investigated.The results showed that water absorption process of CFRP plates corresponded to the two stage model and the maximum water absorption capacity was increased along with the increase of immersion time and temperature.The mechanical and thermodynamic properties were degraded due to the swelling,plasticizing and dissolution of the water absorption.The fatigue life of untreated CFRP plates was decreased with the increase of stress level and the wet lay-up CFRP laminates can carry a sustained stress of 67.87% and 71.85% of its tensile strength without fatigue failure within 2×106 cycles with a reliability of 85% according to the Whitney's method and Sendeckyj's model,respectively.At the stress level of 80%,the fatigue life of specimens at 20°C increased slightly with the immersion time increasing,while those at 40°C and 60°C decreased after immersing 60 days and increased when the immersion time is 180 days.This was attributed to the failure of the interphase and large-sized voids,which leads to uniformly distribution of the tension stress.