In situ X-ray microtomography was used to characterize the changes in internal structure of an expanded thermoplastic polyurethane (eTPU) bead foam used in footwear midsole during compression. Quantitative data on cell size and volume changes based on conventional segmentation were computed. Image correlation on the 4D datasets, i.e. a 3D tomogram collected at various points during deformation, was performed to map the strain fields to aid in analysis of observed deformation. Morphological and structural characterization revealed the gradient porosity and ligament thickness and its influence on the global mechanical behaviour of individual bead foam. The correlation of changes in void size and shape, identified areas of potentially weak regions. Strain maps derived by using voids as markers were adequate to capture the instabilities in local cell collapse. The smaller cells at the surface densified more readily providing more resistance to deformation. In addition, the thicker ligaments in the centre of the bead also aided resistance to deformation. Finally, our results showed the initiation of failure in cell structure was influenced by the heterogeneities around the immediate neighbours in a cluster of voids.

中文翻译：

---

具有独特分级结构的 eTPU 珠粒泡沫压缩行为的原位 X 射线显微断层扫描

原位 X 射线显微断层扫描用于表征压缩过程中用于鞋中底的发泡热塑性聚氨酯 (eTPU) 珠状泡沫的内部结构变化。计算基于常规分割的细胞大小和体积变化的定量数据。对 4D 数据集进行图像相关，即在变形期间在不同点收集的 3D 断层图像，用于绘制应变场以帮助分析观察到的变形。形态和结构表征揭示了梯度孔隙率和韧带厚度及其对单个珠状泡沫的整体力学行为的影响。空隙大小和形状变化的相关性，确定了潜在薄弱区域的区域。通过使用空隙作为标记得出的应变图足以捕捉局部细胞坍塌的不稳定性。表面上较小的细胞更容易致密，从而提供更大的抗变形能力。此外，胎圈中心较厚的韧带也有助于抵抗变形。最后，我们的结果表明，细胞结构失效的开始受到一组空隙中紧邻周围异质性的影响。