Kim H J, Benson R S
Department of Material Science and Engineering, University of Tennessee, Knoxville 37966-2200.
Biomed Mater Eng. 1994;4(3):171-85.
The present work is a study of the effects of soft segment molecular weight and chemical structure on the fatigue crack propagation of model copoly (ether-urethane-urea)s (PEUU). The PEUU were synthesized using polypropylene glycol (PPG), polytetramethylene glycol (PTMG), and polyethylene glycol (PEG) as the soft segment component. The number average molecular weights of the polyethers were within the range of 1000-2000. Methylene bis (4-phenylisocyanate) (MDI) and ethylene diamine were used as the diisocyanate and the chain extender, respectively. The cyclic loading experiments were carried out using a computerized film stretcher that can conduct sinusoidal operation at a constant strain amplitude, strain rate, and frequency. The Rivlin-Thomas tearing energy, T, and the fatigue crack propagation (FCP) rate were selected to characterize the fatigue behavior of the model polyurethanes. An empirical equation was applied to define the fatigue properties of model polyurethanes and to evaluate the fatigue resistance. To investigate the effect of molecular variables on the FCP, the morphological changes caused by structural differences and cyclic stress were determined using dynamic viscoelastometer (Rheovibron), Small Angle X-ray Scattering (SAXS), and Fourier-Transform Infrared (FT-IR) spectroscopy. Mooney-Rivlin plot was used to determine the crosslink density variation. In addition the orientation behavior at the crack tip was characterized by IR dichroism technique using a polarized FT-IR microscope. The results indicated a reasonable relationship between the FCP rates and the hard segment content, crosslink density, and deformation property at the crack tip. However, the initial stage of phase separation and domain disruption behavior did not show a good correlation with the FCP properties of model polyurethanes. Among the model polyurethanes tested, the PEUU with PTMG (Mn = 1000) exhibited the best fatigue resistance at given test condition.
本研究旨在探讨软段分子量和化学结构对模型共聚（醚 - 聚氨酯 - 脲）（PEUU）疲劳裂纹扩展的影响。以聚丙二醇（PPG）、聚四亚甲基二醇（PTMG）和聚乙二醇（PEG）作为软段组分合成了PEUU。聚醚的数均分子量在1000 - 2000范围内。分别使用亚甲基双（4 - 苯基异氰酸酯）（MDI）和乙二胺作为二异氰酸酯和扩链剂。循环加载实验使用计算机控制的薄膜拉伸仪进行，该拉伸仪能够在恒定应变幅度、应变率和频率下进行正弦操作。选择里夫林 - 托马斯撕裂能T和疲劳裂纹扩展（FCP）速率来表征模型聚氨酯的疲劳行为。应用一个经验方程来定义模型聚氨酯的疲劳性能并评估其抗疲劳性。为了研究分子变量对FCP的影响，使用动态粘弹性仪（Rheovibron）、小角X射线散射（SAXS）和傅里叶变换红外（FT - IR）光谱来确定由结构差异和循环应力引起的形态变化。使用穆尼 - 里夫林图来确定交联密度变化。此外，使用偏振傅里叶变换红外显微镜通过红外二色性技术表征裂纹尖端的取向行为。结果表明FCP速率与硬段含量、交联密度以及裂纹尖端的变形性能之间存在合理的关系。然而，相分离和区域破坏行为的初始阶段与模型聚氨酯的FCP性能没有显示出良好的相关性。在所测试的模型聚氨酯中，具有PTMG（Mn = 1000）的PEUU在给定测试条件下表现出最佳的抗疲劳性。
