The effect of fibre alignment on the fatigue behaviour of unidirectional flax fibre composites
Topic(s) : Material science
Co-authors​ :
Ali MOGHIMIARDEKANI (BELGIUM), Jan IVENS (BELGIUM), Aart Willem VAN VUUREAbstract :
Evaluating manufacturing-induced effects, such as fibre misalignment, after the production of composites is crucial for enhancing the reliability of the production process. Additionally, an understanding of the fatigue behaviour allows the prediction of the long-term properties of these materials. An experimental investigation was conducted to explore the influence of fibre alignment on the fatigue behaviour of non-dry unidirectional flax/epoxy biocomposites. Fibres were not dried before production because previous research has demonstrated enhanced moisture durability, as well as savings in cost and effort.
Some researchers have studied the effects of environmental factors, such as humidity, and various constituent variables, including fibre volume fraction, types of fibre and matrix, and fibre architecture, on the fatigue lifetime of these materials[1–3]. However, there has been limited exploration of the impact of fibre misalignment on the fatigue properties of unidirectional NFCs. The tension-tension fatigue of unidirectional flax fibre composites with epoxy matrix was studied, which were prepared by vacuum assisted resin infusion (VARI) and by preparing impregnated fibre bundles (IFBT). X-ray micro-computed tomography was employed to visualize the structure of the NFCs, followed by analysis using VoxTex and Avizo software. The S/N curve results (see Figure 1a) indicate that the IFBT_1st sample exhibits a steeper S/N curve and so a shorter fatigue life[1] compared to the IFBT_2nd and VARI samples. Additionally, by evaluating the 95% confidence level of fatigue data, as shown in Figure 1b, it is observed that the fatigue life of IFBT_2nd is not statistically shorter than that of VARI, despite IFBT_2nd having a steeper S/N curve. The VoxTex output confirms that IFBT_2nd exhibits better in-plane fibre alignment compared to IFBT_1st. Additionally, Avizo results indicate that both IFBT samples (1st and 2nd) have slightly higher void content. Consequently, fatigue parameters such as stiffness during fatigue, permanent strain, and dissipated energy were assessed to identify any differences. The findings reveal that IFBT_1st exhibits the highest permanent strain, lower stiffness, and a shorter fatigue life. Misaligned fibres are likely a contributing factor to this behaviour. In the case of IFBT_2nd and VARI, permanent strain values in both cases are statistically similar. However, the stiffness during fatigue for VARI is slightly higher than for IFBT_2nd, this discrepancy possibly attributed to micro-impregnation issues (void content).
Some researchers have studied the effects of environmental factors, such as humidity, and various constituent variables, including fibre volume fraction, types of fibre and matrix, and fibre architecture, on the fatigue lifetime of these materials[1–3]. However, there has been limited exploration of the impact of fibre misalignment on the fatigue properties of unidirectional NFCs. The tension-tension fatigue of unidirectional flax fibre composites with epoxy matrix was studied, which were prepared by vacuum assisted resin infusion (VARI) and by preparing impregnated fibre bundles (IFBT). X-ray micro-computed tomography was employed to visualize the structure of the NFCs, followed by analysis using VoxTex and Avizo software. The S/N curve results (see Figure 1a) indicate that the IFBT_1st sample exhibits a steeper S/N curve and so a shorter fatigue life[1] compared to the IFBT_2nd and VARI samples. Additionally, by evaluating the 95% confidence level of fatigue data, as shown in Figure 1b, it is observed that the fatigue life of IFBT_2nd is not statistically shorter than that of VARI, despite IFBT_2nd having a steeper S/N curve. The VoxTex output confirms that IFBT_2nd exhibits better in-plane fibre alignment compared to IFBT_1st. Additionally, Avizo results indicate that both IFBT samples (1st and 2nd) have slightly higher void content. Consequently, fatigue parameters such as stiffness during fatigue, permanent strain, and dissipated energy were assessed to identify any differences. The findings reveal that IFBT_1st exhibits the highest permanent strain, lower stiffness, and a shorter fatigue life. Misaligned fibres are likely a contributing factor to this behaviour. In the case of IFBT_2nd and VARI, permanent strain values in both cases are statistically similar. However, the stiffness during fatigue for VARI is slightly higher than for IFBT_2nd, this discrepancy possibly attributed to micro-impregnation issues (void content).