Prompted by environmental legislation and citizens’ awareness induced by global warming effects, the market for plant-fibre reinforced composites has been growing steadily for the past 10-20 years, as observed by the substantial increase in academic and industrial research developments. However, the transition to larger production still requires several uncertainties to be overcome. Among these uncertainties, defects in plant fibres are known to decrease the mechanical properties at the composite scale. It is therefore of interest to better understand the defects nature, origin and consequences at the fibre scale to monitor the use of plant fibres as reinforcement. In recent decades, finite element modelling has emerged in various scientific fields as an interesting tool that complements experimental characterization. Finite element modelling is even more critical for small and intricate elements such as plant fibres where standard mechanical tests require substantial adjustments and investments due to their complex ultrastructure compared to synthetic materials. The main objective of this review is to provide a novel overview of defects found in plant fibres and their influence on the mechanical properties of plant fibres based on experimental and modelling work. Through a top-down and multi-scale approach, we first describe the flax fibre ultrastructure with a focus on defects. Then, advanced testing methods and emerging numerical approaches that capture the complex mechanical behaviour of plants, especially flax fibres, are addressed.

在环境立法和公民由全球变暖效应引起的意识的推动下，植物纤维增强复合材料的市场在过去 10-20 年里一直在稳步增长，正如学术和工业研究发展的大幅增加所观察到的那样。然而，向更大生产的过渡仍然需要克服几个不确定因素。在这些不确定性中，已知植物纤维中的缺陷会降低复合材料的机械性能。因此，更好地了解纤维尺度上的缺陷性质、起源和后果以监测植物纤维作为增强材料的使用是很有意义的。近几十年来，有限元建模作为一种有趣的工具出现在各个科学领域，作为对实验表征的补充。有限元建模对于小而复杂的元素（例如植物纤维）更为重要，因为与合成材料相比，植物纤维的超微结构复杂，因此标准机械测试需要大量调整和投资。本综述的主要目的是基于实验和建模工作，对植物纤维中发现的缺陷及其对植物纤维机械性能的影响提供新的概述。通过自上而下和多尺度的方法，我们首先描述了亚麻纤维的超微结构，重点是缺陷。然后，解决了捕获植物（尤其是亚麻纤维）复杂机械行为的先进测试方法和新兴数值方法。