UNIVERSITY OF MASSACHUSETTS
Objectives: As wind turbine sizes scale up, the manufacturing-induced defects (specifically wrinkling or out-of-plane buckling) associated with large-scale composite blades will affect the integrity and reliability of the entire energy generation system, impacting all blade manufacturers. To address this problem, the proposed research will focus on three primary objectives: Process Optimization Models: To understand the cause of such manufacturing-induced defects and minimize or eliminate such defects through material selection, part design and process improvements based on validated forming models; Effect of Defects: To understand and quantify what effect these wrinkling defects have on resulting blade performance, static overload failure, and fatigue failure; and Digital Image Correlation: To develop a rapid, large-area method for the detection of such defects in manufactured blades using digital image correlation (DIC), a new sensing technique for structural health monitoring and quality assurance. The overall objective of this program is to significantly reduce the need for overly conservative (i.e., expensive) or ineffective assumptions of applied safety factors (i.e., unanticipated risk) in the go/no-go criteria established for production quality control. Project Description: Both coupon-level studies and 'full-scale' experiments on a 9-m blade will be conducted. Coupon studies will focus on quantifying the critical wrinkle amplitudes and resultant strain amplifications that can lead to premature failure. To represent full-scale structural effects, two 9-m blades (NW100 or CX100 design) will be fabricated at TPI. Validation of the process modeling will be done by comparing the location of observed defects to model predictions. Detailed blade-defect identification will be conducted through nondestructive inspection (NDI) using both UML's DIC system and other NDI techniques routinely used at SNL. One blade will be sectioned for localized fatigue testing, while the other blade will be sent for full-scale fatigue testing at NREL. Project Impact: The two primary 'products' from this program are the process modeling software for minimizing wrinkles and the DIC full-field measurement technique, both informed by the understanding of the effect of the wrinkle defect and the resulting critical flaw size. These manufacturing quality control and operations monitoring products are based on commercial, off-the-shelf systems that will be enhanced for specific application to composite wind turbine blades. The proposed work will thus provide directly transferable solutions spanning almost all aspects of blade design, development, manufacturing and inspection. Based on this work, materials suppliers can develop fiber architectures that provide greater stability against wrinkle formation; structural and process engineers will have a tool to interrogate design details such as ply thickness, orientation, ply drops, and vacuum application rates; tool designers will have a new insight into how the interactions of surface geometry, process rates and materials can be modified to mitigate wrinkle defects; and engineers will have a tool to assess whether a blade goes on the tower when wrinkles are identified. The net result will be a measurable reduction in the cost of energy based on improved material utilization, reduction in manufacturing costs and a rational approach to product disposition in the presence of defects.