ＡｒＦＲＰの引張と疲労における層間はく離進展特性に及ぼす水環境効果

Abstract

An investigation has been carried out concerning the influences of water absorption on the tensile and fatigue properties of two kinds of (0°/±45°/90°)2s aramid fiber/epoxy composites, i.e., Kevlar 49 and HM50 composites. The delamination growth behavior was quantitatively evaluated with a scanning acoustic microscope. The specimens used were dry and wet ones, which were respectively preconditioned in air and in water at 80°C for two months. Under a static tensile loading, for both wet and dry specimens, resin cracking and interfacial debonding in the weakest 90° ply were followed by the lowering of load carrying capacity of 90° and 45° plies, and the final fracture was caused through an increase in 0° ply stress. Resin cracking in wet specimens was observed at a lower stress level than in dry ones, because water absorption lowered the interfacial strength between fiber and matrix, i.e., lowering of the interlaminar strength of laminates. Under a fatigue loading, compliance changes were divided into three regions, i.e., Region I, II and II'. In the cases of dry specimens in air and wet specimens in air, compliance was kept constant in Region I and was increased in Region II. In the case of wet specimens in water, however, Region I was diminished and Region II started from the beginning of the fatigue test owing to the water absorption through the 90° ply cracking. The influence of water absorption on delamination growth behavior was also discussed based upon the observation of ply-to-ply delamination with a scanning acoustic microscope.