热氧老化对纬编双轴向多层衬纱织物增强复合材料力学性能的影响

通过改变预制体结构衬纱取向的方法制备了几种含不同剪切角的纬编双轴向多层衬纱(Multilayered biaxial weft knitted,MBWK)织物增强复合材料。基于Arrhenius模型和Ozawa法设计了热氧老化试验，采用力学性能测试、DSC、FTIR和DMA测试对老化前后的试样热-物理性能进行了表征。实验结果表明：预制体的纱线剪切角不同，其复合材料受热氧老化后力学性能的保留率也显著不同，由于乙烯基酯树脂在热氧老化环境中会发生后固化现象，因此复合材料的弯曲模量在老化过程中呈现先增加后下降的趋势，而拉伸性能则受到增强体结构的影响，纤维/基体界面的结合力退化使拉伸模量在老化过程中持续下降；随着老化时间的延长，树脂的固化度逐渐增加，玻璃化转变温度T_g逐渐升高，储能模量峰值在老化初期由于分子链交联上升，老化后期分子链断裂占据主导作用致使峰值逐渐下降。

Effect of thermo-oxidative aging on the mechanical properties of multi-layered biaxial weft knitted fabric reinforced composites

Several multilayered biaxial weft knitted (MBWK) fabric reinforced composites with different shear angles were prepared by changing the orientation of preform inserting yarns. The thermo-oxidative aging test was designed based on Arrhenius model and Ozawa method. The thermal and physical properties of the samples before and after aging were characterized by mechanical properties, DSC, FTIR and DMA tests. The experimental results show that: With the change of yarns’ shearing angle, the composite mechanical properties retention rate after thermo-oxidative aging is also significantly different, because the post curing will occur for the vinyl ester resin in the thermo-oxidative aging environment. Therefore, the bending modulus of the composite materials in the aging process presents downward trend after increased first, and the tensile properties are affected by the reinforcement structure. The degradation of adhesion strength at fiber/matrix interface makes the tensile modulus decrease continuously during the aging process. With the aging time prolongation, the curing degree of resin increases gradually, and the glass transition temperature T_g increases gradually. The peak value of energy storage modulus increases at the initial stage of aging due to molecular chain crosslinking, while decreasing of the peak value is caused by molecular chain fracture at the later stage of aging.