Evaluating Structural Failure of Load-Carrying Composite Box Beams with Different Geometries and Load Conditions

The load-carrying component of wind turbine blades is a composite box beam that often consists of two spar caps and two shear webs. Local buckling of such beams usually leads to failure of spar caps and/or shear webs. As the failure modes change with cross-sectional geometries and load conditions, it is of interest to develop a method for efficient structural failure evaluation. As a correlation exists between linear buckling response and the potential structural failure, this study presents comprehensive numerical studies on the box beams with different external shapes and layer thicknesses to establish buckling mode maps that can be useful for the preliminary structural design. The results show that the changes of cross-sectional aspect ratio affect the buckling strength more than the change of the weight or the material usage when the spar cap buckling dominates the failure. Larger curvature of spar caps can significantly improve the buckling strength due to better resistance to the cross-sectional flattening. The evaluation method only uses the modeling techniques readily available in common commercial FE software, and no in-house user subroutines is needed, thus allowing the failure evaluation to be performed efficiently in the early design of the load-carrying box beams in wind turbine blades.