| With the increasing use of advanced resin matrix composite materials in the aviation field,some problems of the widely used autoclave technology are exposed. Firstly, it is more difficult to achieve the integral forming by one step. Secondly, preparation, storage and transportation of prepregs cost too much. Thirdly, paving layer efficiency is low, it is difficult for automatic paving layer to cover more complex structure.Vacuum assisted resin infusion(VARI)technology is a typical and cost-effective liquid composite molding technique, which has some advantages that other traditional technology do not have. By use of this technology, we can not only molding large and complex components that with sandwich, bars and embedded parts by one step, but also oriented-laying fibers according to the structural requirements. In addition, the cost of equipment and technology is not so high. However, composites manufactured by VARI with high content of pores and defects have uneven thickness and fiber volume fraction, also have low fiber volume content, due to its low molding pressure. That causes the mechanical performance can not meet the requirements of aeronautical composite materials, which restricting the application of VARI technology in aerospace structures seriously.As the problem of low fiber volume and poor mechanical properties of the elevator manufactured by VARI in our country, this paper designed a new type of molding technology named autoclave/VARI technology that combined autoclave and VARI together. The main contents and results include the following aspects:In this paper, the new type of molding technology named autoclave/VARI technology was designed. In this design, we just need to add a special resin trap that could bear high temperature and pressure, and autoclave transforming is unnecessary. The cost is cheap and the risk is low, so meet the molding requirements. The thickness, fiber volume content and mechanical properties of the composite manufactured by autoclave/VARI technology were measured. And these properties of the composites, that manufactured respectively by VARI and autoclave/VARI technology, werecompared with each other. The results show that, the autoclave/VARI sample has smaller thickness and higher fiber volume fraction, and its fiber volume fraction can reach 65%, which only 55%when it comes to VARI sample. Also its mechanical properties are better than VARI sample and its pores and resin enrichment area are less. It has more dense fibers and more excellent inter-layer combination as well.The effect of dwell pressure on thickness, fiber volume content and mechanical properties were studied. Results show that, the higher the dwell pressure, the less the thickness and porosity content, and the higher the dense carbon fibers, fiber volume fraction and modulus. When the pressure reaches about 200 KPa, the thickness, fiber volume fraction(about 65%) and modulus are no longer change, and the pore disappears. With the increase of dwell pressure, ±45° in-plane shear strength almost remains constant, 90° tensile strength has a rising trend, but the trend is not obvious. The higher the dwell pressure, the greater the short beam shear strength, then it decreases and leveled off finally, 0° tensile strength has no obvious regularity.The effect of dwell time on thickness, fiber volume content and mechanical properties, etc were studied. It turns out that, the longer the dwell time, the less the thickness and porosity content,and the higher the dense carbon fibers, fiber volume fraction and modulus. When the time up to 20 min, the thickness, fiber volume fraction and modulus are no longer change any more, and at the same time the pore disappears. With the increase of dwell pressure, ±45° in-plane shear strength almost remains constant, 90° tensile strength has a rising trend, but the trend is not obvious, and in the meantime short beam shear strength decreases first and leveled off finally, 0° tensile strength shows the tendency of decreased first then increased. |
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