Manufacturing processes of natural fiber reinforced polymer (NFRP) composites are becoming the interest of industrials and scientists because these eco-friendly materials are emerging in automotive and aerospace industries. In this context, machining processes of NFRP composites present significant issues related to the complex structure of natural fibers that need thorough tribological studies. This paper aims to explore the effect of natural fiber orientation on the machinability of NFRP composites using Merchant model in order to separate the shearing energy from the friction energy. Orthogonal cutting process is conducted on unidirectional flax fibers reinforced polypropylene composites by changing the fiber orientation from 0° to 90° with respect to the cutting direction. Iosipescu shear tests are also performed to determine the mechanical shear behavior in function of the fiber orientation. Results show the applicability of Merchant model on the machining analysis of NFRP composites by verifying the main model assumptions. The fiber orientation affects significantly the shearing and the friction energies that control the cutting behavior and the chip formation of the NFRP composite. The resulted machined surfaces are hence intimately related to the natural fiber orientation.

天然纤维增强聚合物（NFRP）复合材料的制造工艺正在引起工业界和科学家的兴趣，因为这些环保材料正在汽车和航空航天工业中兴起。在这种情况下，NFRP复合材料的加工过程提出了与天然纤维复杂结构相关的重大问题，需要进行彻底的摩擦学研究。本文旨在利用Merchant模型探讨天然纤维取向对NFRP复合材料可加工性的影响，以将剪切能与摩擦能分开。通过将纤维相对于切割方向的方向从0°更改为90°，对单向亚麻纤维增强的聚丙烯复合材料进行正交切割工艺。还进行了Iosipescu剪切测试，以确定与纤维取向有关的机械剪切行为。结果表明，通过验证主要模型假设，Merchant模型可用于NFRP复合材料的机械加工分析。纤维取向会显着影响剪切力和摩擦能，从而控制NFRP复合材料的切削性能和切屑形成。因此，所得到的机加工表面与天然纤维的取向密切相关。纤维取向会显着影响剪切力和摩擦能，从而控制NFRP复合材料的切削性能和切屑形成。因此，所得到的机加工表面与天然纤维的取向密切相关。纤维取向会显着影响剪切力和摩擦能，从而控制NFRP复合材料的切削性能和切屑形成。因此，所得到的机加工表面与天然纤维的取向密切相关。