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

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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