Development of Fatigue Properties Evaluation System for Mesoscopic Component for Composite Materials

为了研究复合材料的界面强度，提出了微观复合材料试验方法。该试验保持了真实复合材料中纤维和基体的边界条件，使在界面上测量屈服和断裂成为可能。采用电磁作动器，研制了专用的极低负荷疲劳试验机。研究结果总结如下：(1)电磁致动器专用低负荷能力疲劳试验系统的研制利用专用电磁致动器研制了容量为2.5N的新型疲劳试验机。这台试验机可以控制很小的负载，小到10mN。开发该驱动器的关键是碟形弹簧，它能保证加载轴方向的准确性。成功地进行了极低载荷（几十mN）下的疲劳试验，低载荷疲劳试验系统的研制已基本完成。(2)静载荷和疲劳载荷下不同界面强度的复合材料细观构件试验采用不同的阳极氧化法对PAN基碳纤维进行不同程度的表面处理。酸功能随电量的增加而线性增加。然后，制造了一种称为“微复合材料”的模型复合材料。在微复合材料中，中心纤维被六种纤维包围，其中浸渍了树脂。中心纤维的边界条件与实际复合材料中纤维的边界条件相似。通过拔出中心纤维来测定界面强度。静载荷作用下的界面强度取决于纤维的表面处理。而纤维表面处理对疲劳载荷下的界面强度没有影响。不同应力比下的疲劳试验结果表明，以最大应力表示疲劳强度时，应力比的影响可以忽略不计。(3)与宏观疲劳性能的比较宏观II型疲劳分层的应力比依赖性与界面疲劳试验完全不同。因此，虽然加载方式相似，但疲劳断裂的机理却完全不同。少

Micro composite test was proposed in this study in order to investigate the interfacial strength of composites. This test keeps the boundary condition of fibers and matrix in real composites, and makes it possible to measure the yield and fracture on the interface. Special fatigue testing machine with very low-load capacity was developed for this microcomposite tests by using electromagnetic actuator. The results are summarized as follows :(1) Development of special low-load capacity fatigue testing system with electromagnetic actuatorA new type fatigue testing machine of the capacity of 2.5N was developed by using a special electromagnetic actuator. This testing machine can control a very small load down to 10mN.The key point for developing this actuator is the disc type spring which keeps the accuracy of the direction of the loading shaft. Fatigue tests at very low load (several tens of mN) were carried out successfully, and the development of the low-load fatigue testing system was … More almost finished.(2) Composite mesoscopic component tests with different interfacial strength under static and fatigue loadingsDifferent levels of surface treatment were carried out on PAN based carbon fiber by varying the amount of electricity through the anodic oxidation method. Acid function increased linearly with increasing the amount of electricity. Then, a model composite which is called "micro composite" was manufactured. In micro composite, the central fiber is surrounded by six fibers, and resin was impregnated among them. The boundary condition of the central fiber is similar to that of fiber in real composites. Interfacial strength was measured by pulling out the central fiber. The interfacial strength under static loading depends on the surface treatment of fiber. However, the interfacial strength under fatigue loading was not influenced by the surface treatment of fiber. The results of fatigue tests under different stress ratios showed that the effect of stress ratio was negligible when the fatigue strength is expressed by the maximum stress.(3) Comparison with macroscopic fatigue propertiesThe stress-ratio dependency of macroscopic mode II fatigue delamination was completely different from that of interfacial fatigue test. Thus, the mechanism of fatigue fracture is completely different, although the loading mode was similar. Less