Recent studies of carbon fiber and carbon/glass hybrid laminates have reported compression strengths and failure strains which are borderline for wind turbine blade designs, depending upon the reinforcement architecture, matrix resin, and environment. Compressive strength is known to be sensitive to the straightness of the fibers, with even relatively small degrees of waviness or misalignment causing significant decreases in compression properties. The effects of fiber waviness, induced by infusion processes and inherent in fabric architectures, on compressive strength, have been investigated. Structural details such as ply drops and ply joints can cause significant levels of fiber misalignment, depending on parameters such as ply thickness, fraction of plies dropped, ply drop location, ply joint gap, and mold geometry and pressure. These parameters have been varied in the study reported in this paper, with compressive properties determined in each case. The results show that prepreg laminates containing ply drops and joints can provide adequate compressive strength, but that severe knockdowns can occur for geometries where large misalignments are induced.

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Application of different damage modeling approaches for use with composite materials and composite material structures has grown with increasing computational ability. However, assumptions are often made for "worst case" scenarios with these modeling techniques In order to develop a tool that will allow for accurate analysis of a complete structure, modeling approaches must be optimized by including defects of different parameters. It was the optimization of these approaches that was investigated herein with specific application toward establishing a protocol to understand and quantify the effects of defects in composite wind turbine blades. A systematic, three-round study of increasing complexity was performed to understand the effects of three typical blade manufacturing defects while investigating continuum, discrete, and combined damage modeling. Through the three rounds of the benchmark material testing, significant coupon level testing was performed to generalize the effects of these defects. In addition, material properties and responses were analyzed and then utilized as material inputs and correlation criteria for each analytical technique. A standard defect case was initially used for each modeling technique and correlation was compared both qualitatively and quantitatively. While each modeling type offered certain attributes, a combined approach yielded the most accurate analytical/experimental correlation. Thus, a unique comparison of several different analytical approaches to composites with respect to manufacturing for consistency, accuracy, and predictive capability allowing for improved blade reliability and composite structural assessment. NomenclatureBRC = Blade Reliability Collaborative MSUCG = Montana State University Composites Group BMT = Benchmark Material Testing OP = Out-of-plane wave IP = In-plane wave CDM = Continuum Damage Model DDM = Discrete Damage Model UMAT = User Material Subroutine σ = Stress ε = Strain u = Displacement