Short fiber reinforced polymer composites processed by selective laser sintering (SLS) generally show an oriented fiber structure, which leads to anisotropic properties of fabricated components. However, the formation mechanism of fiber orientation is barely investigated. In this study, the oriented structure of the carbon fiber/polyamide12 composites processed by SLS is characterized using the X-ray computed tomography, and the role of powder-spreading in formation of the fiber orientation is investigated by simulation using the discrete element method. The short fibers in the fabricated sample show preferred alignment along the spreading direction (X direction) and perpendicular to the building direction (Z direction), even with the orthogonal scanning path. The formation of fiber orientation is attributed to the powder-spreading process. During the powder-spreading process, the particle pile experiences a shearing flow along the building direction, where the higher the Z position, the faster the X-direction speed of the particle flow. Consequently, short fibers driven by the torque caused by the shearing flow gradually rotate and align to the spreading direction, leading to the anisotropy in the final products. The strength of the shearing flow can be tailored by adjusting the spreading parameters such as layer thickness, spreading speed and rotating speed of the roller. Potential approaches to tailor the fiber orientation during the powder-spreading procedure of SLS are discussed.

通过选择性激光烧结（SLS）处理的短纤维增强聚合物复合材料通常显示出定向的纤维结构，这导致了制成部件的各向异性。但是，几乎没有研究纤维取向的形成机理。在这项研究中，使用X射线计算机断层扫描技术表征了SLS处理的碳纤维/聚酰胺12复合材料的取向结构，并通过离散元素方法模拟研究了粉末分布在纤维取向形成中的作用。即使在正交扫描路径下，制成的样品中的短纤维也表现出沿扩展方向（X方向）和垂直于构建方向（Z方向）的最佳排列。纤维取向的形成归因于粉末铺展过程。在散粉过程中，粒子堆沿构建方向经历剪切流，其中Z位置越高，粒子流的X方向速度越快。因此，由剪切流引起的扭矩驱动的短纤维逐渐旋转并与铺展方向对齐，从而导致最终产品中的各向异性。剪切流的强度可以通过调整铺展参数（例如层的厚度，铺展速度和辊的旋转速度）来调整。讨论了在SLS撒粉过程中调整纤维取向的潜在方法。因此，由剪切流引起的扭矩驱动的短纤维逐渐旋转并与铺展方向对齐，从而导致最终产品中的各向异性。剪切流的强度可以通过调整铺展参数（例如层的厚度，铺展速度和辊的旋转速度）来调整。讨论了在SLS撒粉过程中调整纤维取向的潜在方法。因此，由剪切流引起的扭矩驱动的短纤维逐渐旋转并与铺展方向对齐，从而导致最终产品中的各向异性。剪切流的强度可以通过调整铺展参数（例如层的厚度，铺展速度和辊的旋转速度）来调整。讨论了在SLS撒粉过程中调整纤维取向的潜在方法。