Influence of Environment on Fracture Behavior of High-Strength, High-Modulus Fibers and Nanoscopic AFM Damage Evaluation

本研究项目的重点是高强度和高弹性模量纤维的断裂行为，陶瓷前体型纤维和芳族聚酰胺纤维。特别注意的是，断裂行为的测试环境的影响，和纳米表面损伤的原子力显微镜（AFM）进行评估。为了进行具有微米级小直径的纤维的拉伸和疲劳测试，使用了专门设计的测试机，该测试机能够进行机械测试，包括在受控环境中对诸如纤维的微小元件进行疲劳测试。通过电磁致动器向试样施加载荷。测试机配备有一个可以控制环境（如真空、湿和/或干气体）的腔室。包括γ-氧化铝（Altex ®）的陶瓷纤维的纵向弹性模量，SiC（Nicalon）和Si-Ti-C-O（Tyranno））独立于测试环境，即，真空、空气和去离子水。然而，准静态纤维强度在真空中是最高的，并在空气中，在水中的顺序下降：纤维强度随环境中的水含量的增加，并随着位移（应变）率降低。类似于陶瓷纤维，芳族聚酰胺纤维的断裂强度对测试环境敏感：包括Kevlar（<<0！>>）纤维和Technora^<<O！>>）纤维的纵向弹性模量和断裂强度随吸水率的增加而降低。当在真空中测试时，Kevlar 49的空气预处理的纤维强度（<<0！>>）在空气中进行的下降。至于疲劳，Kevalr 49纤维与金属材料相比具有上级的抗疲劳性。然而，在真空中进行的拉-拉疲劳强度高于在实验室空气中进行的。用原子力显微镜（AFM）对纤维表面损伤进行了研究，并对纤维的降解和断裂/疲劳机理进行了讨论。

This research project focuses the fracture behavior of high-strength and high elastic modulus fibers, i.e., ceramic precursor type fibers and aramid fibers. Special attention is paid to the influence of an testing environment on the fracture behavior, and nanometric surface damage is evaluated with atomic force microscopy (AFM). In order to conduct tensile and fatigue testing of fibers with small diameter of micrometers, a specially designed testing machine, which enables mechanical testing including fatigue of microelements such as fibers in a controlled environment was used. Loads are applied to a specimen by means of an electromagnetic actuator. The testing machine is equipped with a chamber which can control environments such as vacuum, wet and/or dry gases. The longitudinal elastic modulus of the ceramic fibers including gamma-alumina (Altex^<<O!>>), SiC (Nicalon), and Si-Ti-C-O (Tyranno^<<O!>>))were independent of testing environment, i.e., vacuum, air and deionized water. However, the quasi-static fiber strength in vacuum was the highest, and decreased in the order of in air, and in water : the fiber strength decreased with increasing water content in an environment, and with decreasing displacement(strain)rate. Similarly to ceramic fibers, the fracture strength of aramid fibers was sensitive to a testing environment : the mechanical properties of aramid fibers including Kevlar^<<O!>>) fibers and Technora^<<O!>>) fiber, longitudinal elastic modulus and fracture strength, decreased by water absorption. When tested in vacuum, the air-preconditioned fiber strength of Kevlar 49^<<O!>>) decreased from that conducted in air. As for fatigue, the Kevalr 49 fiber had superior fatigue resistance compared with metallic materials. However, the tension-tension fatigue strength conducted in vacuum was higher than that conducted in laboratory air. The fiber surface damage was examined by an AFM,and the degradation and fracture/fatigue mechanisms are discussed.