| Vacuum assisted resin transfer molding (VARTM) process is a new type of sandwich structure molding method, which is rapid molding, environmental-friendly and cost-efficiency. Products prepared with this processing method is light-weighted and with good properties. Opening grooves on the foam core will greatly improve the mold filling speed and production efficiency, and also enhance the interfacial properties between the structural core materials and the panels, which make it especially suitable for the preparation of large-scale, reinforced and shaped structural parts. Therefore, the process has been widely used in wind power, aerospace, transportation as well as other fields.To obtain saturated resin flow characteristics in the groove, this paper investigated the flow behavior of epoxy resin and silicone oil inside the PVC rigid foam wall channel via pressure-driven flow experiment. We found that a lot of roughness elements which were composed of broken or cracked bubbles distributed on the inner wall of the foam channel wall, and these roughness elements of different size and irregular distribution caused the mobility of the fluid in the foam wall channel to be only around 60% of that in the smooth wall channel. Equivalent permeability was used to characterize the mobility of the resin in non-seepage foam wall channel, and a calculation formula of equivalent permeability in the grooves was obtained.The unsaturated flow behavior inside the channel was studied by computer simulation. We found that after the flow starting, the flow rate increased rapidly to a value from zero, and then decreased monotonically with increasing the flow time, and the decline scale of the flow rate decreased. As the flow went on, the drop of pressure consumption in the saturated region behind the flow front increased. With increasing the flow channel diameter and the contact angle between the resin and the inner wall of the grooves, the equivalent permeability of the simulated channel gradually approached that of the parallel plate flow channel, and a calculation formula of equivalent permeability in the grooves with comprehensive consideration of the influence of contact angle and the channel diameter was obtained.For the resin flow in the groove-typed VARTM process, the equivalent permeability was used to characterize the mobility of the resin inside a non-seepage foam wall channel and the resin flow within the pre-forming fiber was regarded as an incompressible fluid flow in porous medium. Therefore, Darcy's law and the conservation of mass can be used to describe the resin flow. This paper aimed at optimizing the mold filling time to the shortest, based on which the parameters of the groove (groove width, groove depth, groove pitch) were optimized by numerical simulation. Two-dimensional and three-dimensional flow simulation results showed that when the groove width was 1-3mm, groove spacing was 20-50mm, the mold filling time is shorter. Also within these range, the greater the width and spacing of the groove were, the shorter the filling time was. However, with the groove width increased, and with the groove spacing decreased, the resin consumption would increase and thus resulted in higher production costs. Therefore, when designing grooves, resin consumption and filling time should be taken into account, preferably the groove width should be designed in the range of [1,3] mm, and appropriate groove spacing should be within [20,50] mm. Finally, by the groove-type VARTM process experiment, the above simulation results were verified. |
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