As a typical additive manufacturing process, fused filament fabrication (FFF) commonly utilizes a cooling fan to speed up cooling and solidification of thermoplastic melts, thereby preventing the melts from flowing and improving the manufacturing quality. However, the temperature gradient created by the cooling fan often induces nonuniform crystallization, and further affects the mechanical properties in subsequent service, particularly for the thermoplastics polyether ether ketone (PEEK) with a high processing temperature. Therefore, tracing the dynamic crystallization is the key issue to achieve an integrated simulation suitable for analyzing the material-process-property relationship, and ultimately to improve the manufacturing quality. In this study, we developed a continuous phase-evolution model, suitable in the process simulation of FFF manufacturing of PEEK. Compared with existing phase-evolution models, this developed model considers the potential plastic deformation of continuously formed crystals in subsequent service. Each newly formed crystal phase is modeled by one newly added elastic-plastic branch with an initial stress-free state. Therefore, both the initial configuration at the formation moment and its impacts on the subsequent plastic deformation can be traced. By introducing the effective phase concept, the continuous added phases are equivalent to one effective phase, significantly reducing the computational burden of dynamic crystallization in PEEK. Consequently, the developed model can be implemented into the user defined subroutine for the finite element analysis, and the FFF manufacturing can be modeled by the element activation technology according to the real manufacturing path. To validate the developed model, the FFF manufacturing of a quadrangular prism specimen and the subsequent nanoindentation tests were studied. Both the crystallinity evolution during manufacturing and the mechanical properties in subsequent nanoindentation tests, respectively, at the downwind side and at the upwind side can be well predicted, indicating that the developed method can be used to design the FFF manufacturing process of engineering components.

中文翻译：

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熔丝制备中 PEEK 的不均匀结晶及其对后续机械性能的影响

作为一种典型的增材制造工艺，熔丝制造 （FFF） 通常利用冷却风扇来加速热塑性熔体的冷却和凝固，从而防止熔体流动并提高制造质量。然而，冷却风扇产生的温度梯度通常会导致不均匀的结晶，并进一步影响后续使用的机械性能，特别是对于加工温度较高的热塑性聚醚醚酮 （PEEK）。因此，追踪动态结晶是实现适用于分析材料-过程-性能关系的集成仿真并最终提高制造质量的关键问题。在这项研究中，我们开发了一个连续相演化模型，适用于 PEEK 的 FFF 制造过程模拟。与现有的相演化模型相比，该开发的模型考虑了连续形成的晶体在后续服务中的潜在塑性变形。每个新形成的晶相都由一个新添加的具有初始无应力状态的弹塑性分支建模。因此，可以追踪形成时刻的初始构型及其对后续塑性变形的影响。通过引入有效相概念，连续添加的相相当于一个有效相，显著减轻了 PEEK 中动态结晶的计算负担。因此，开发的模型可以实现到用户定义的有限元分析子程序中，并且 FFF 制造可以根据实际制造路径通过元件激活技术进行建模。 为了验证开发的模型，研究了四棱柱试样的 FFF 制造和随后的纳米压痕测试。在下风侧和上风侧，制造过程中的结晶度演变和后续纳米压痕测试中的机械性能都可以很好地预测，表明所开发的方法可用于设计工程部件的 FFF 制造工艺。