Simulating the Manufacturing Process and Subsequent Structural Stiffness of Composite Wind Turbine Blades with and without Defects

Abstract

Traditional ply-based and zone-based models are limited in their ability to account for the fiber directions resulting from the forming of fabric-reinforced composite wind turbine blades. Compounding the problem is the presence of defects such as resin-rich pockets of the polymer matrix due to out-of-plane and in-plane waves resulting from the manufacturing process. As a result, blades are typically overdesigned, unnecessarily increasing weight and material costs. 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 fabric layers. Using experimental shear, tensile, bending, and friction data to characterize the mechanical behavior of the fabric layers, the model captures in-plane yarn waviness and changes in the in-plane yarn orientations as they 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 resulting from the resin-infused fabrics can be calculated. The methodology can thereby link the resulting bending and torsional stiffnesses of the blade back to the manufacturing process. This paper discusses the methodology for determining the material properties of the beam and shell elements in their final orientations in the cured composite to predict the structural stiffness of a wind turbine blade.

Predictive model for the detection of out-of-plane defects formed during textile-composite manufacture

“…For example, a stitched biaxial non-crimp fabric (NCF), like that shown in Fig. 2b, is discretized using the same unit cell as for a woven fabric [22,23]. Note that the approach employed in the current research does not explicitly model stitches.…”

“…Furthermore, the shared node at the intersection of beam elements enforces the primary function of the stitching, which is to secure the position of layers within a single ply. The model for the NCF considered in this research was previously validated to ensure that the fabric behavior is properly simulated using this FE approach [23]. However, a modeling technique has been developed to model stitches explicitly for NCFs whose behavior is not adequately captured by the unit cell of Fig.…”

Investigation into the changes in bending stiffness of a textile reinforced composite due to in-plane fabric shear: Part 1 – Experiment

“…This approach relies heavily on experimental processes to determine the deformation of the fabric during the manufacturing process and the resulting structural behavior of the final composite part. The design-build-test methodology is very time consuming and expensive, so models are often used as a complementary virtual design tool to aid in predicting the final orientations of the fiber tows within a part as a result of manufacturing [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. A recent investigation by Mitchell et al [35] was performed to demonstrate how the output of such a simulation of the composite manufacturing process can facilitate a subsequent finite element model which would use the geometry of the deformed textile to predict the behavior of the final composite structure.…”

“…The picture-frame test is performed by clamping a sample of fabric to a pin-jointed frame. A load is applied in the bias direction of the frame, which creates a state of pure shear in the fabric [9,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. An example of a picture-frame test is shown in Fig.…”

Investigation into the changes in bending stiffness of a textile reinforced composite due to in-plane fabric shear: Part 2 – Numerical analysis

“…1. Many researchers have presented finite element models that consider the mechanical behavior of the textile during the manufacture of a composite structure to predict the final orientations of the fiber tows [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. These simulations aid in the design of molds used to form the material and to assist in the selection of fabrics to satisfy the drapability requirements of the part geometry.…”