Carbon fiber reinforced facing/aramid honeycomb core sandwich composite materials were studied through three point bending test. In order to clarify the influences of water on the stiffness and strength, the dry and wet specimens were used. At the same time, the fractured specimens were inspected by a scanning electron microscope (SEM) and a scanning acoustic microscope (SAM) to observe the superficial and interior fractures of the specimens, respectively, and the fracture mechanism was analyzed. The experimental results showed the following.
(1) Sandwich material increased the bending stiffness a little after its absorption of 6wt.% water, but decreased the shearing stiffness by about 10%.
(2) Water absorption affected the core shearing strength more than the facing strength.
(3) The strength of interface between the facing layer and core of sandwich materials was larger than that of the matrix resin.
(4) The buckling axis was observed on the compressive fracture surface of the wet specimens more than that of the dry specimens, which shows that most fibers in the wet specimens are fractured by compressive stress.
(5) In case of short span beams whose length was shorter than 200mm, the wet specimens flexed more than the dry specimens. It is thought to be caused by the degradation of cell wall of the core.