Investigating the influence of High-Void content on the impact and Post-Impact properties of Flax/Epoxy composite laminates with different stacking configurations

Defects in composite materials, such as voids, significantly impact their long-term performance and should be carefully considered in the design process of engineering structures. This study investigates the effects of high void content on the impact and post-impact properties of pure Flax/Epoxy (FE) composite laminates. Three main configurations, namely cross-ply (CFE), angle-ply FE (AFE), and quasi-isotropic FE (QFE), are examined using drop-weight impact and three-point bending tests. The results reveal distinct behavior among the configurations. The drop-weight impact test results show that the AFE configuration exhibits 3.5% and 6.45% higher impact resistance compared to CFE and QFE, respectively. to the increase of the impact energy to 15J amplifies the differences to 9.31% and 19.11 %. Also, post-impact flexion tests demonstrate a significant decline in flax composite resistance by 14% for CFE, 26% for QFE, and AFE. Furthermore, the overall impact and flexural properties of the FE composites are not significantly affected by the void content. However, it has a major impact on the damage mechanism that is ispected visually and through X-ray tomography, emphasizing the importance of considering the void content in the design and analysis of such flax composites. The proposed numerical model to predict the onset of damage and damage evolution in these composite materials under low velocity impact show a good greement with the experimental results.