3D Permeability of Thick-section Off-axis Glass Fabric Vinyl ester Composite by VARIM Processing

Abstract

The vacuum-assisted resin infusion molding (VARIM) method has been increasingly used in manufacturing large composite structures, such as MW-scale wind turbine blades, due to structural size, cost-effectiveness and out-of-autoclave curing requirements. Among various material and processing parameters, 3D permeability of composites with thick section laminate construction is critical in controlling resin flow in an efficient manufacturing process development and in accurate numerical modeling and simulations. Resin flow in a mold with complex geometries, such as a wind turbine blade with a perforated foam core and multiple fabric orientations, is affected by its through-thickness, 3D permeability. The objectives of this research are to: (1) establish analytical models to include 3D flow and off-axis flow front tracking, and (2) determine orientation and principal components of permeability tensor for two types of E-glass fabrics in both homogeneous and symmetric, hybrid lay-ups, such as those found in a spar cap. The number of fabric layers is varied to investigate scaling and compressibility. A noninvasive point infusion method with vinyl ester resin as the infusing medium was used. In experiments, the flow front was tracked by a video camera, and both the laminate thickness and the mass flow rate were measured. The measurement method required an isotropic transform solution for the Laplace equation to relate the flow rate through the inlet tube, Darcy’s Law, and an expanding hemisphere. The orientation of the principal axes was calculated by comparing the in-plane flow front along the 0°, 45° and 90° axes. The analytical models provide a method to describe the permeability tensor with the flow front position, laminate thickness and fabric and resin properties as the only inputs. The results provided reasonable values for the components of the permeability tensor and demonstrated that the analytical models behaved well as laminate thickness and the flow front radius increased.