Abstract
The Marine Energy Advanced Materials project is an ongoing, multiyear, multilaboratory project with the main goals of addressing barriers and uncertainties facing marine energy developers in adopting advanced materials for structural applications. The National Renewable Energy Laboratory’s (NREL’s) goals for the project were to address subcomponent testing needs for marine energy materials, improve understanding of design allowables at full scale, and provide near-net-scale static and fatigue data of composite subcomponents using materials applicable to the marine energy industry. In the long term, the test method development and data generated will be used to inform standards development. This report outlines perhaps one of the largestscale studies conducted with regard to saltwater conditioning of various composite material subcomponents and their subsequent structural validation, specifically directed at the marine renewable energy industry. A variety of fiberglass composite panels with epoxy and vinyl ester epoxy resin systems were manufactured at Montana State University and were then used to manufacture an array of different types of subcomponent test specimens at NREL’s Flatirons Campus. These subcomponents were in the form of T-bolt and double-ended-insert specimens, which were intended to represent bonded and mechanical bolted connections for thick composite laminates, metal-metal and composite lap shear specimens to evaluate adhesion of constituent materials, and adhesive beam-shear specimens as part of an effort to better evaluate the characteristics of thick adhesive bondlines. Overall, the materials used were fiberglass reinforced epoxy and vinyl ester matrix composites, epoxy and methacrylate adhesives, and 316 and 2507 stainless steels. Specimens were then conditioned in salt water at various temperatures and for various periods of time at Florida Atlantic University and Pacific Northwest National Laboratory. All specimens were mechanically characterized and validated using various test methods under static and fatigue loading conditions at NREL’s Structural Technology Laboratory. Throughout the conditioning and mechanical validation process, valuable experience was gained, which will help guide future test method development for marine energy materials. In many instances, the results were similar to what had been observed during previous coupon-scale characterization efforts that provided a vital understanding of the scale-up process. However, in some instances, unexpected phenomena were observed, such as interactions between the adhesives and 316 steel. Furthermore, some materials exhibited significant degradation due to the saltwater conditioning. Ultimately, this report provides a detailed summary of the specimens that were designed, the subcomponent test methods that were developed, and the results that were generated, which will serve as important guidance for marine renewable energy developers and researchers for future structural designs and validation.