Fused filament fabrication (FFF) has seen broad industrial adoption as it is capable of manufaturing large complex parts from robust thermoplastics in a cost-effective manner. However, the mechanical performance of the printed parts is limited due to poor interlayer bonding and the presence of voids. In order to overcome these drawbacks, the addition of short or continuous fibers into the polymer matrix has been investigated, as the fibers can act as a mechanical reinforcement while also mitigating residual stress resulting from the material's rapid solidification following extrusion. Therefore, understanding the implications of process parameters and fiber reinforcements on printed part properties through detailed crystallization analysis and rheological characterizations is of paramount importance. The goal of this study is to understand the process–structure–property relationships of short carbon fiber-reinforced polyamide 6 (CF-PA6) by comparing the melt rheology and crystallinity of CF-PA6 versus a neat PA6 polymer. Differences in the melting and crystallization behavior resulting from the reinforcing fibers revealed an increased time window for crystallization in the fiber-reinforced matrix. Rheological characterizations at the recommended printing temperatures demonstrate the shear-thinning behavior of the samples at shear rates relevant to FFF. From a statistical design of experiments analysis, the layer thickness was found to be the most significant parameter affecting the tensile properties of a printed part at a constant printing temperature and printing speed. The tensile fracture surfaces of the printed specimens using scanning electron microscopy were analyzed to provide insights into the failure mechanisms as a function of AM processing variables.

中文翻译：

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使用基于材料挤出的增材制造制造的尼龙-碳纤维复合材料的流变学研究

熔融长丝制造 (FFF) 已在工业上得到广泛采用，因为它能够以具有成本效益的方式从坚固的热塑性塑料制造大型复杂部件。然而，由于层间结合不良和空隙的存在，打印部件的机械性能受到限制。为了克服这些缺点，已经研究了将短纤维或连续纤维添加到聚合物基体中，因为纤维可以作为机械增强材料，同时还可以减轻挤出后材料快速固化所产生的残余应力。因此，通过详细的结晶分析和流变学表征了解工艺参数和纤维增强材料对打印部件性能的影响至关重要。本研究的目的是通过比较 CF-PA6 与纯 PA6 聚合物的熔体流变性和结晶度，了解短​​碳纤维增强聚酰胺 6 (CF-PA6) 的工艺-结构-性能关系。由增强纤维引起的熔化和结晶行为的差异表明纤维增强基体中结晶的时间窗口增加。在推荐的印刷温度下的流变特性证明了样品在与 FFF 相关的剪切速率下的剪切稀化行为。从实验分析的统计设计中，发现层厚度是在恒定打印温度和打印速度下影响打印部件拉伸性能的最重要参数。