Interfacial degradation is the main reason for deterioration of mechanical properties of composites in hydrothermal environments. In this study, the effect of the interphase on water diffusion in two types of unidirectional continuous carbon fiber-reinforced polyamide 6 (CF/PA6) composites is investigated through experimental measurements, theoretical analysis, and numerical simulation. The moisture diffusion coefficient of composite at different environmental temperatures is characterized by water immersion tests for analyzing the barrier and accelerating effects of the interphase layer. Based on the experimental results, the three-phase Halpin–Tsai model is derived and validated, and then the critical diffusivity is obtained to quantify the interfacial effect during the diffusion process. To further validate the present three-phase Halpin–Tsai model, the stable and transient finite element models of moisture diffusion are developed. It is found that the critical diffusivity coefficient of the interphase for the CF/PA6 composite system is 7.31 times higher than that of the matrix.

中文翻译：

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改进的Halpin-Tsai方程用于预测水扩散过程中的界面效应

界面降解是在水热环境中复合材料机械性能下降的主要原因。在这项研究中，通过实验测量，理论分析和数值模拟，研究了相间对两种类型的单向连续碳纤维增强聚酰胺6（CF / PA6）复合材料中水扩散的影响。复合材料在不同环境温度下的水分扩散系数通过水浸试验来表征，以分析相间层的阻隔和加速作用。根据实验结果，导出并验证了三相Halpin-Tsai模型，然后获得了临界扩散系数，以量化扩散过程中的界面效应。为了进一步验证当前的三相Halpin-Tsai模型，建立了水分扩散的稳定和瞬态有限元模型。结果表明，CF / PA6复合体系的相间临界扩散系数比基体的临界扩散系数高7.31倍。