关键词: 夹芯结构, 泡沫壁, 真空辅助树脂传递模塑成型, 等效渗透率, 沟槽

Abstract: Foam core sandwich panels are widely used in many technical fields, especially in aerospace and wind power structures, due to their high specific strength and high specific stiffness. Among the various manufacturing processes for sandwich panels, vacuum assisted resin transfer molding (VARTM) is used extensively for manufacturing large composite structures. The success of VARTM depends upon the complete filling of the mold with adequate wetting of the fiber preform. The addition of grooves on the surface of the low-density core is used to shorten the fill time, because of the high permeability of grooves. Therefore, the resin flow through the grooves is an important step to ensure that the resin infusion process can be finished before the resin gels. The flow characteristics in grooves with impermeable foam walls for sandwich panels were investigated through experimental observations. An empirical equation for the volume flow rate in a glass tube and cylindrical grooves with impermeable foam walls was obtained. It was shown that the volume flow rate was a function of pressure drop, pipe dimension and fluid viscosity. When compared to pipe flow with no-slip boundary conditions, the flow ability in grooves dropped by about 40%. This was ascribed to the rough surface of grooves and demonstrated by scanning electron microscope (SEM),which clearly showed that there were many broken or uncracked bubbles distributed in the foam walls. An equivalent permeability was introduced to describe the flow capacity in the grooves. The grooves were treated as a porous medium whose permeability represented the average flow capacity in grooves,and the empirical Darcy’s Law was used to calculate the average velocity in grooves. Then the equivalent permeability equation for pipe flow in grooves with impermeable foam walls was obtained. This equation can be used for quick engineering estimate of equivalent permeability in grooves.

Key words: sandwich structure, foam wall, vacuum assisted resin transfer molding, equivalent permeability, grooves