Simulation of the manufacturing process and subsequent structural stiffness of a composite wind turbine blade with and without defects

The stiffness of a polymer resin-infused composite wind turbine blade is a function of the fiber volume fraction and the respective orientations of the fibers in the plies. Traditional ply-based and zone-based structural-composite models depend on a user-prescribed fiber orientation in the respective plies and therefore can require multiple tedious definitions to account for changes in the fiber directions resulting from the composite manufacturing process. Without the micromanaging of these fiber orientations, these traditional composites models may not necessarily truly quantify the blade structural stiffness, which may lead to a compromised prediction of the state of strain due to an applied load. Compounding the challenge of modeling the state of strain is the presence of defects, such as resin-rich pockets (resulting from out-of-plane waves) and in-plane waves that can develop during the manufacturing process. The formation of these two types of waves is a consequence of the combination of the part geometry, fabric architecture, and manufacturing process parameters. As a result, composite wind turbine blades are typically overdesigned to compensate for the presence of defects and for the uncertainties in the fiber orientations, thereby increasing weight and material costs over what they could be.;In the current research, a methodology is presented for simulating the manufacturing process for fabric-reinforced composite wind turbine blades using Abaqus/Explicit. The methodology captures the evolution of the yarn directions during the forming process thereby allowing for a map of the fiber orientations throughout the blade. A hybrid approach using conventional beam and shell elements is used to model the various non-crimp fabric layers. By experimentally characterizing the mechanical behavior of the fabric and resin materials used in a blade's design and incorporating the respective material behaviors in user-supplied material models, the forming simulation can give insight into the formability of a given fabric to a given geometry, and can capture fabric stresses, in-plane yarn waviness and changes in the in-plane yarn orientations as the layers of fabric conform to the shape of the mold, as well as out-of-plane wave defects as a result of the manufacturing process. Subsequently, after the fabric layers have been laid into the mold and the final yarn orientations are known, the structural stiffness of the blade can be calculated. The methodology can thereby link the resulting bending and torsional stiffnesses of the composite structure back to the manufacturing process and predict locations in the blade that may develop defects. This methodology can then be used to guide changes in fabric selection and the manufacturing process to avoid needlessly overdesigning a composite blade.