Study on Dynamic Environmental Strength of Advanced High-Strength, High-Rigidity Fiber Reinforced Composites.

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The advanced composite materials investigated are 1) Two types of carbon fiber reinforced epoxy resins (CFRP) (normal type and heat-resistant type), 2) A carbon fiber reinforced PEEK resin (CFRTP), 3) Two types of aramid fiber reinforced epoxy resins (ARFRP) (Kevlar 49^<(R)> and Technola^<(R)> fiber reinforcements), and 4) A silicon carbide whisker reinforced aluminum alloy. In the present study, in-situ observation by means of an acoustic emission (AE) analysis, evaluation of internal damage by means of a scanning acoustic microscope (SAM), and SEM observation of fracture surface are combined to elucidate tensile and fatigue fracture mechanisms and fatigue crack growth characteristics. Moreover, hygrothermal degradation of FRP and corrosion damage in water of SiCw/Al are made clear. Two-dimensional images of internal damages can be clearly observed by SAM, and SAM fractography is proved to be quite useful. Synthesized AE analyses including the distributions of AE amplitude, AE event duration, and AE frequency, give us useful and powerful information to analyze the complicated fracture mechanisms of composite materials. The water absorption characteristics depends upon the type of epoxy resins so much. Water absorption causes plasticization of epoxy resin, thereby improving mechanical properties of FRP. Also water absorption causes resin degradation and weakening of fiber/resin interfaces, thereby reducing the strength of FRP. In addition, splitting of aramid fibers by water absorption further decreases the strength of ARFRP. SiC whisker so much improves mechanical properties of SiCw/Al alloy, but local cells composed between SiC whisker and Al matrix lower the strength of the composite. The mode I delamination resistance of CFRTP hardly accelerated in water, and the capability of damage tolerance of CFRTP is so high compared to that of CFRP.