Abstract
Load carrying components of modern wind turbine blades are manufactured from composites, consisting of non-crimp fabrics infused with polymer resins. The effective stiffness of the resulting laminate is a combination of the properties of its building blocks i.e. fibers, and matrix as well as from the fabric texture imperfections e.g. fiber undulations. Moreover, ply inherent boundary conditions, e.g. the restriction of the Poisson deformation of the matrix imposed from the adjacent fibers, are determining the in-situ orthotropic performance. Towards modelling the in-plane stiffness of a unidirectional (UD) infused non-crimp fabric, a two-step modular procedure is proposed, accounting for the aforementioned parameters, based only on experimental data and analytical formulations. Initially, a micromechanical model is predicting the stiffness of the ideal UD ply i.e. disregarding fiber undulations. Subsequently, a plate model is generated based on the classical lamination theory, approximating the UD laminate as a multiaxial configuration of ideal UD sub-plies. Each sub-ply thickness and orientation is based on the fiber angle density distribution of dry fabrics and cured laminates. These are derived experimentally with an integrated optical camera system and Computer Tomography scans respectively. The theoretical laminate stiffness is correlating very well with standard and thick UD laminate quasi-static tests.
Highlights
IntroductionWind turbine blades are subjected in high cycle fatigue loads over their operational life span [1]
Wind turbine blades are subjected in high cycle fatigue loads over their operational life span [1].Especially in the edge-wise direction these loads are driven from the blade mass [2]
Load carrying components of modern wind turbine blades are manufactured from composites, consisting of non-crimp fabrics infused with polymer resins
Summary
Wind turbine blades are subjected in high cycle fatigue loads over their operational life span [1]. The model is considering the matrix in-situ stiffening due to the Poisson deformation restriction, resulting from the adjacent fibers and the fiber in-plane angle distribution of the non-crimp fabric. A hexagonal pack scheme is considered and the corresponding UD composite ply properties EE⊥h, GG⊥||h, (stiffness transverse to the fibers and in-plane shear stiffness), are described in eq (4) and (5). Elastic properties of the multilayer laminate Based on the fiber angle distribution measurements of the dry fabrics and the cured laminates, the UD configurations can be approximated as the summation of UD sub-plies with a range of fiber orientation. The experimental in-plane angle distribution for the 4-layer and the 22-layer laminates before and after infusion with the corresponding bell-shaped probability densities are shown in Figure 5 and Figure 6
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