Scaling effects in the manufacture and testing of grid-stiffened composite structures

Scaling effects in the manufacture and testing of glass fiber-reinforced epoxy grid-stiffened structures have been investigated in this study. Four nominally identical scaled sizes of mold have been manufactured, in which the length, width, height, and internal channel sizes were varied to achieve ¼, ½, ¾ and full-scale stiffened structures. The panels were manufactured on a glass mold using the vacuum-assisted resin transfer molding technique, enabling the flow front to be monitored throughout the filling process. Grid-stiffened beams were removed from the cured panels and tested in flexure on scaled bending fixtures. The vacuum-assisted resin transfer molding manufacturing study on the four scaled sizes indicated that resin infusion incurred more rapidly in the smallest mold, possibly due to difficulties in accurately cutting the glass fabric, which in turn reduced the effective areal density of the fabric, thereby modifying its effective permeability. The flow rates and velocities of the resin fronts in the larger mold sizes were similar, suggesting that an appropriately scaled mold can be used to successfully predict the infusion process in more representative structures. Flexural tests on the grid-stiffened samples highlighted a similar response in the three largest samples, with the smallest sample again offering a modified response. Similar failure mechanisms, including fracture of the grid structure, debonding at the skin-core interface, and flexural failure in the center of the sample, were observed in all of the samples.