Measurement and analysis on in-plane and through-thickness air permeation of fiber/resin prepreg

Nowadays, zero-bleeding process and out-of-autoclave process are prevailing for aircraft composite structures. For these cases, the prepreg property such as air permeability becomes a crucial element for entrapped air venting off from prepreg stack during cure process. Therefore, the measurement of air permeability is important for the understanding and optimization of autoclave and vacuum-bag processes to obtain void-free composite parts. In this paper, an air permeation measuring system was established to test in-plane and through-thickness air permeabilities of prepreg stack, and the effects of compacting pressure and temperature on the air permeability were investigated. Furthermore, the influences of air permeability of prepreg stack on the void characteristics inside the cured laminates processed by autoclave and vacuum-bag processes were analyzed. The results indicate that the proposed air permeation measuring systems can quantitatively measure the in-plane and through-thickness gas permeabilities of prepreg stack. The compacting pressure and temperature have important effects on air permeability. For the same prepreg system, the in-plane air permeability is two orders of magnitudes higher than the through-thickness one. Finally, void defects are sensitive to the air permeability for vacuum-bag process, especially in the case of thick laminates. It provides an effective way to evaluate the quality of the prepreg for control of void defect and an important guideline for prepreg manufacturers.