This article presents the effect analysis of the printing time sequences on the mechanical properties in correlation with the crystallization kinetics and rheological behavior. For this purpose, two printing order of 3D printed samples (printed simultaneously or in sequence) were chosen. In addition, two different infill patterns (line and gyroid) and building directions (horizontal and vertical) have been used. Concerning the polymer filaments, two commercial polylactic acid (PLA 3D870 and PLA 3D850) having different crystallization kinetics were used. The effect of the printing time delay between each layer on the temperature profile and the crystallization evolution was studied using a finite element analysis method simulation. The simulation results show a greater thermal excursion for longer delay times between the layers and with a crystallization degree evolution characterized by a step pattern. Moreover, a major density of crystals appears in the center of the final part. A new approach was adapted to measure the volumetric contraction of the material as a function of the temperature; it was performed with a gap test using a rotational rheometer under static conditions (without external deformation). The normal force measured from the test has shown a faster and higher increase of the contraction for the material with faster crystallization kinetics and with a higher degree of crystallinity. The results concerning the tensile properties show better rigidity for the samples printed in sequence due to the minor time of delay between the deposited layers. The mesostructure of the printed parts was analyzed with an X-ray tomography and a scanning electron microscope. The highest difference is presented from the PLA 3D870 characterized by the highest rate of crystallization resulting in more microvoids compared with the PLA 3D850, due to the less welding cohesion between the layers.

中文翻译：

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3D 打印温度曲线对聚合物材料行为的影响

本文介绍了印刷时间序列对与结晶动力学和流变行为相关的机械性能的影响分析。为此，选择了 3D 打印样品的两个打印顺序（同时或按顺序打印）。此外，还使用了两种不同的填充模式（直线和陀螺）和建筑方向（水平和垂直）。关于聚合物长丝，使用了两种具有不同结晶动力学的商业聚乳酸（PLA 3D870 和 PLA 3D850）。使用有限元分析方法模拟研究了每层之间的印刷时间延迟对温度分布和结晶演变的影响。模拟结果表明，层间延迟时间越长，热漂移越大，结晶度演化呈阶梯状。此外，晶体的主要密度出现在最终部件的中心。采用一种新方法来测量材料的体积收缩随温度的变化；它是在静态条件下（没有外部变形）使用旋转流变仪进行间隙测试。从测试中测得的法向力表明，对于具有更快结晶动力学和更高结晶度的材料，收缩会更快和更高地增加。由于沉积层之间的延迟时间较短，有关拉伸性能的结果显示顺序打印的样品具有更好的刚性。使用 X 射线断层扫描和扫描电子显微镜分析打印部件的细观结构。与 PLA 3D850 相比，PLA 3D870 的差异最大，其特点是结晶率最高，由于各层之间的焊接内聚力较低，因此与 PLA 3D850 相比，微孔较多。