The aim of this study is to investigate the fatigue behaviour of hybrid flax-glass/epoxy composites under repeated impact loading subsequent to water ageing. Different plates of these composite materials were fabricated using the vacuum infusion technique. Five stacking sequences were considered: [F8], [G/F3]S, [G2/F2]S, [G3/F]S, and [G8], where F and G stand for flax/epoxy and glass/epoxy plies, respectively. Water ageing was conducted by immersing the composite specimens in tap water at room temperature for various durations, and until saturation was reached. Fatigue impact tests were carried out using three impact energies: 3, 4, and 5 J. An advanced high-resolution camera was used to monitor the evolution of damage mechanisms occurring on the non-impacted surfaces, while a laser thermometer was considered to track the temperature variations within each composite specimen. The obtained results show that flax-glass hybridization reduces the mass of absorbed water in flax/epoxy composite by up to 70%. Furthermore, there is a more pronounced decrease in longitudinal modulus and maximum stress in aged composites, with reductions of up to 70% compared to unaged ones. Additionally, visible damage occurs even at low energy levels, manifesting from the initial impacts in both aged and unaged composite laminates. Moreover, a correlation between the number of impacts to failure and the cumulative energy is revealed. Ultimately, water aging reduces the strength of the studied composite laminates and their resistance to impact fatigue. Furthermore, the hybrid laminates with high proportion of flax layers are particularly susceptible to water ageing effects.

中文翻译：

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水老化下冲击疲劳混合亚麻玻璃/环氧树脂复合材料的损伤研究


本研究的目的是研究混合亚麻玻璃/环氧树脂复合材料在水老化后重复冲击载荷下的疲劳行为。使用真空灌注技术制造了这些复合材料的不同板。考虑了五种堆叠顺序：[F8]、[G/F3]S、[G2/F2]S、[G3/F]S 和 [G8]，其中 F 和 G 代表亚麻/环氧树脂和玻璃/环氧树脂层， 分别。通过将复合材料样品在室温下的自来水中浸泡不同的持续时间来进行水老化，直至达到饱和。使用三种冲击能量进行疲劳冲击测试：3、4 和 5 J。使用先进的高分辨率相机来监测非冲击表面上发生的损坏机制的演变，同时考虑使用激光温度计来跟踪每个复合样本内的温度变化。所得结果表明，亚麻-玻璃杂化可将亚麻/环氧树脂复合材料中吸收的水质量减少高达 70%。此外，老化复合材料的纵向模量和最大应力下降更为明显，与未老化复合材料相比，下降幅度高达 70%。此外，即使在低能量水平下也会发生明显的损坏，这从老化和未老化复合材料层压板的初始冲击中可见一斑。此外，还揭示了失效冲击次数与累积能量之间的相关性。最终，水老化会降低所研究的复合材料层压板的强度及其抗冲击疲劳性。此外，具有高比例亚麻层的混合层压板特别容易受到水老化效应的影响。