Widespread attention to make use of biodegradable resources as a replacement for petroleum products leads to the exploitation of natural fiber reinforced composites. Natural fiber reinforced polymer composites usually exhibit lower mechanical properties than synthetic fiber ones. Thus, understanding key factors affecting the overall mechanical properties in order to increase them is crucial. One underlying factor is the length of fiber highly contributing to the extent of matrix/fiber interfacial load transfer at the interface. However, the concurrent examination of the load transfer mechanism at the interface of fiber/matrix in terms of fiber length has not been well performed using computational, analytical and experimental approaches. This work is aimed at the determination of the critical fiber length associated with a full load transfer condition using various methods to better understand their accuracy and the interfacial load transfer mechanism. For this purpose, specimens of neat polypropylene (PP) and 20 wt% kenaf/PP composites were fabricated using extrusion injection molding. Tensile testing, scanning electron microscopy and density measurements were conducted to incorporate the obtained results into the models and to verify the results predicted by the models. A three dimensional representative volume element (RVE) representing the filler content of fabricated specimens was assumed. A micromechanical model was employed to make the results of analysis independent of the RVE dimensions. The critical fiber length for a full load transfer was determined by evaluating the stored elastic strain energy changes against the fiber length. The results showed that the kenaf fiber length is critical to both the load transfer efficiency and stiffening of composites. The results further revealed that to obtain the full interfacial load transfer, the length of kenaf fibers needs to be greater than the critical length being ∼2.4 mm provided that perfect kenaf/PP interfacial interaction exists.

利用生物可降解资源替代石油产品的广泛关注导致对天然纤维增强复合材料的开发。天然纤维增强的聚合物复合材料通常表现出比合成纤维低的机械性能。因此，了解影响整体机械性能的关键因素以提高它们至关重要。一个基本因素是纤维的长度对界面处基质/纤维界面载荷转移的程度有很大的影响。然而，利用计算，分析和实验方法不能很好地同时进行纤维/基体界面处的载荷传递机制的检查。这项工作旨在使用各种方法确定与满负荷转移条件相关的临界纤维长度，以更好地了解其准确性和界面负荷转移机制。为此，使用挤出注塑成型法制备了纯聚丙烯（PP）和20 wt％的洋麻/ PP复合材料的样品。进行拉伸测试，扫描电子显微镜和密度测量，以将获得的结果合并到模型中并验证模型预测的结果。假定一个三维代表性的体积元素（RVE），代表制作样品的填料含量。使用微机械模型使分析结果与RVE尺寸无关。通过评估存储的弹性应变能相对于纤维长度的变化来确定全负荷转移的临界纤维长度。结果表明，洋麻纤维长度对于复合材料的载荷传递效率和刚性至关重要。结果进一步表明，要获得完整的界面载荷转移，洋麻纤维的长度必须大于临界长度〜2.4 mm，前提是存在完美的洋麻/ PP界面相互作用。