Abstract

Aramid fibers, with superior mechanical properties, have been widely used in a lot of industrial fields. From a safety point of view, long-term durability is required for these aramid fibers. In this study, the fatigue and tensile properties of two types of single aramid fibers, poly(para-phenylene terephthalamide) (PPTA) and poly(para-phenylene-co-3,4′-oxydiphenylene terephthalamide) (PPODTA), were investigated. Single fiber tensile and fatigue tests, cyclic tensile tests, tensile tests for post-fatigue test specimens, and optical microscopic observations were conducted. The stress–strain curves of the cyclic tensile tests indicated that PPTA and PPODTA fibers could be deformed above the elastic limit, and the strain at 2.0 GPa stress and the initial tensile modulus in subsequent tensile tests were changed by the cyclic stress. In fatigue tests, the cumulative probabilities of fatigue failure increased with the number of stress cycles for both the PPTA and PPODTA fibers. The fatigue behavior was influenced by the stress conditions and gauge length of the specimens. The initial tensile modulus in subsequent tensile tests was increased by the fatigue tests for both the PPTA and PPODTA fibers. However, regarding the tensile strength, significant decreases due to the fatigue tests were not observed. Fibrils detached from the fiber surface were observed in the post-fatigue test PPTA and PPODTA fiber specimens by optical microscope observations, with the loss of these fibrils contributing to the changes in modulus.

摘要

具有优异机械性能的芳族聚酰胺纤维已被广泛用于许多工业领域。从安全角度考虑，这些芳族聚酰胺纤维需要长期的耐久性。在这项研究中，两种类型的单芳族聚酰胺纤维，聚（的疲劳性能和拉伸性能对位亚苯基对苯二甲酰胺）（PPTA）和聚（对研究了-亚苯基-co-3,4'-氧二亚苯基对苯二甲酰胺（PPODTA）。进行了单纤维拉伸和疲劳测试，循环拉伸测试，疲劳后试样的拉伸测试以及光学显微镜观察。循环拉伸试验的应力-应变曲线表明，PPTA和PPODTA纤维可能会在弹性极限以上变形，而2.0 GPa应力下的应变和后续拉伸试验中的初始拉伸模量会因循环应力而发生变化。在疲劳测试中，PPTA和PPODTA纤维的疲劳破坏累积概率均随应力循环次数的增加而增加。疲劳行为受应力条件和试样长度的影响。PPTA和PPODTA纤维的疲劳试验都增加了后续拉伸试验中的初始拉伸模量。然而，关于拉伸强度，未观察到由于疲劳试验而显着降低。在疲劳后测试PPTA和PPODTA纤维样品中，通过光学显微镜观察观察到从纤维表面分离的原纤维，这些原纤维的损失有助于模量的变化。