Effects of defects in composite wind turbine blades. Round 1.

The Wind Turbine Blade Reliability Collaborative (BRC) was formed with the goal of improving wind turbine blade reliability. Led by Sandia National Laboratories (SNL), the BRC is made up of wind farm maintenance companies, turbine manufacturers and third party investigators. Specific tasks have been assigned by SNL to the various parties. The portion of the BRC that will focus on establishing the criticality of manufacturing defects (aka, Effect of Defects) is being researched by the Montana State University Composites Group (MSUCG). The research described herein compiles the second round of a multi-year year plan consisting of three rounds of work performed by Montana State University (MSU) within two areas—Flaw Characterization and Effects of Defects. The purpose of this document is to capture and convey the progress which has been made by the MSU team under the first round of the effort. The work presented has established that characterization of defects common to wind turbine blades is possible. A consistent framework has been established and validated for quantitative categorization and analysis of flaws. With proper characterization, it is possible to establish the structural implication of a flaw. Applying the characterization techniques described herein to incoming data will enable the generation of a statistically significant and comprehensive flaw database. It is the goal of this investigation that these tools and data, once disseminated to industry, will contributed to improvements in the reliability of wind turbines. Understanding the changes in the material properties associated with characterized flaws has been achieved on a coupon level with physical testing being performed with several configurations of several different flaw types. This testing clearly indicated that fiber misalignment and porosity resulted in degraded material properties and decreased material performance. To complement and work toward predicting these types of results, simple modeling efforts have been performed and reasonable agreement has been achieved when compared to the test data. Additional work is necessary to improve the accuracy and a more complex modeling effort will be undertaken in the future. Work will continue with efforts to acquire as-built flaw data to ensure the characterized flaws are representative of full-scale wind turbine blades. In addition, research will be performed into reliability methods suitable for wind turbine composites. Finally, characterization of second round test specimens for use in model validation and physical testing correlation through the use of improved and more accurate models.