Residual alignment and its effect on weld strength in material-extrusion 3D-printing of polylactic acid
Residual alignment and its effect on weld strength in material-extrusion 3D-printing of polylactic acid
复制标题
DOI：
10.1016/j.addma.2020.101415
复制
发表时间：
2020-12-01
影响因子：
11
通讯作者：
McIlroy, Claire
中科院分区：
文献类型：
--
作者：
Costanzo, Andrea;Spotorno, Roberto;McIlroy, Claire
获得材料挤出（MatEx）3D打印的分子理解对于预测和控制零件性能至关重要。在这里，我们报告的直接观察到的独特的双折射定位到焊接区域之间的打印长丝，表示存在的分子取向，是不存在的大部分的长丝。在焊缝处的双折射值在较高的打印速度和较低的喷嘴温度下增加，并且被发现对通过垂直于打印方向的拉伸测试测量的焊缝强度是有害的。我们采用分子意识的MatEx流动和冷却过程的非等温模型来预测在玻璃化转变时被困在焊缝中的对齐程度。我们发现，预测的剩余对准因子，（A）在酒吧，是线性相关的双折射的程度，Δ n。因此，通过结合实验和分子建模，我们表明，焊接强度是不受限制的相互扩散，如通常预期的，而是由缠结的聚合物网络的配置。我们采用经典的玻璃态聚合物断裂的分子解释来解释测量的焊接强度如何随着打印速度的增加和喷嘴温度的降低而降低。
Gaining a molecular understanding of material extrusion (MatEx) 3D printing is crucial to predicting and controlling part properties. Here we report the direct observation of distinct birefringence localised to the weld regions between the printed filaments, indicating the presence of molecular orientation that is absent from the bulk of the filament. The value of birefringence at the weld increases at higher prints speeds and lower nozzle temperatures, and is found to be detrimental to the weld strength measured by tensile testing perpendicular to the print direction. We employ a molecularly-aware non-isothermal model of the MatEx flow and cooling process to predict the degree of alignment trapped in the weld at the glass transition. We find that the predicted residual alignment factor, (A) over bar, is linearly related to the extent of birefringence, Delta n. Thus, by combining experiments and molecular modelling, we show that weld strength is not limited by inter-diffusion, as commonly expected, but instead by the configuration of the entangled polymer network. We adapt the classic molecular interpretation of glassy polymer fracture to explain how the measured weld strength decreases with increasing print speed and decreasing nozzle temperature.