With flax fabric as the reinforcement and unsaturated polyester as the matrix,composites of two,three,and four layers were fabricated respectively by the vacuum assisted resin infusion(VARI)technique.Tensile strength of the composites after being saturated in the water for different durations was tested.The tensile strength of the two-layer composites was decreased after being soaked in the water for two,three,and six month,respectively.For the three and four layers specimens,the tensile strength was decreased initially with water treatment.After reaching the minimum,the tensile strength was increased.Scanning electron microscopy(SEM)confirmed that it might be contributed to the thickness of the two-layer composites.The thinner specimen is easier to be damaged by the penetrated moisture owing to the delamination between the fiber and the matrix after water immersion.For the three and four layers specimens,their contradictory tensile strength suggests that the thicker specimen can delay the moisture permeation and is of better water durability.
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