Patterson Brian M, Henderson Kevin, Gilbertson Robert D, Tornga Stephanie, Cordes Nikolaus L, Chavez Manuel E, Smith Zachary
Los Alamos National Laboratory,Polymers and Coating Group,Materials Science and Technology Division,P.O. Box 1663,MS E549,Los Alamos,NM 87545,USA.
Microsc Microanal. 2014 Aug;20(4):1284-93. doi: 10.1017/S1431927614000993. Epub 2014 May 20.
Meso-scale structure in polymeric foams determines the mechanical properties of the material. Density variations, even more than variations in the anisotropic void structure, can greatly vary the compressive and tensile response of the material. With their diverse use as both a structural material and space filler, polyurethane (PU) foams are widely studied. In this manuscript, quantitative measures of the density and anisotropic structure are provided by using micro X-ray computed tomography (microCT) to better understand the results of mechanical testing. MicroCT illustrates the variation in the density, cell morphology, size, shape, and orientation in different regions in blown foam due to the velocity profile near the casting surface. "Interrupted" in situ imaging of the material during compression of these sub-regions indicates the pathways of the structural response to the mechanical load and the changes in cell morphology as a result. It is found that molded PU foam has a 6 mm thick "skin" of higher density and highly eccentric morphological structure that leads to wide variations in mechanical performance depending upon sampling location. This comparison is necessary to understand the mechanical performance of the anisotropic structure.
聚合物泡沫中的中尺度结构决定了材料的力学性能。密度变化，甚至比各向异性孔隙结构的变化更能极大地改变材料的压缩和拉伸响应。聚氨酯（PU）泡沫作为结构材料和空间填充材料有多种用途，因此得到了广泛研究。在本论文中，通过使用微型X射线计算机断层扫描（microCT）提供密度和各向异性结构的定量测量，以便更好地理解力学测试结果。MicroCT显示了由于浇铸表面附近的速度分布，发泡泡沫不同区域的密度、泡孔形态、尺寸、形状和取向的变化。在这些子区域压缩过程中对材料进行“中断式”原位成像，揭示了结构对机械载荷的响应路径以及由此导致的泡孔形态变化。研究发现，模塑PU泡沫有一层6毫米厚的“表皮”，其密度较高且形态结构高度偏心，这导致根据取样位置不同，力学性能有很大差异。这种比较对于理解各向异性结构的力学性能是必要的。
