Studies on structural and performance changes under dynamic loads, such as cyclic tension, are limited. We synthesized a casting polyurethane based on 1,5-naphthalene diisocyanate with exceptional fatigue resistance, capable of withstanding up to 700,000 cycles of flexural fatigue. Tensile fatigue tests were conducted at a stretching strain amplitude of 100%, a frequency of 10 Hz, and cycles ranging from 10,000 to 100,000 to investigate the microstructures and properties. Atomic force microscopy revealed a gradual decrease in the high modulus region content, while the medium modulus region initially increased and then decreased, and the low modulus region showed an increasing trend. Transmission electron microscopy images clearly depicted the destruction process of spherulites: crystal bundles initially separated from the spherulites, and with increasing cycles, these crystal bundles became smaller, eventually evolving into “small black dots” after 100,000 cycles. Wide-angle and small-angle X-ray diffraction analyses indicated that crystallinity, grain size, and long period decreased, while the transition layer thickness increased. We further explored the correlation between structural evolution and performance, elucidating the underlying mechanisms. This study provides crucial insights into the performance of casting polyurethanes under dynamic loading, valuable for designing durable, fatigue-resistant materials.

中文翻译：

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1,5-萘二异氰酸酯 （NDI） 基浇注聚氨酯的动态载荷响应：微观结构和机械演变研究


对动态载荷 （如循环拉伸） 下的结构和性能变化的研究是有限的。我们合成了一种基于 1,5-萘二异氰酸酯的浇注聚氨酯，具有优异的抗疲劳性，能够承受高达 700,000 次的弯曲疲劳循环。拉伸疲劳试验在 100% 的拉伸应变幅值、10 Hz 的频率和 10,000 至 100,000 次的循环范围内进行，以研究微观结构和性能。原子力显微镜显示高模量区含量逐渐降低，中等模量区先增加后减少，低模量区呈增加趋势。透射电子显微镜图像清楚地描绘了球晶的破坏过程：晶束最初与球晶分离，随着循环次数的增加，这些晶束变小，最终在 100,000 次循环后演变成“小黑点”。广角和小角 X 射线衍射分析表明，结晶度、晶粒尺寸和长周期减小，而过渡层厚度增加。我们进一步探索了结构进化与性能之间的相关性，阐明了潜在的机制。这项研究为铸造聚氨酯在动态载荷下的性能提供了重要见解，对于设计耐用、抗疲劳的材料很有价值。