Adhesive Bonds and Wind Turbine Blade Failure: An Industry Perspective

Wind turbine blades are large composite structures with demanding performance requirements and commercial pressures toward low costs. Adhesive bonds are critical structural elements in most blades. A 140 m long blade may have 800 m of structural adhesive bond lines composed of toughened epoxy adhesive. Adhesive bond lines typically connect the two shells at the leading and trailing edges of the blade and connect the shell-integrated spar caps with one or more shear webs. In addition, co-bonded interfaces (bonds between pre-cured components and infused resin) are present within most modern blades, both in the originally manufactured structure and in repairs to blade structure. In the authors’ experience, failures of adhesive bonds are among the leading causes of wind turbine blade structural damage and failures. While blade failures are rare occurrences, when they do occur, the consequences can be significant. While much has been written on adhesion and adhesive bonds, there are few publicly available references that provide detailed information on failures of wind turbine blade bonds. Blade manufacturers or wind energy project owners and/or operators do not typically disclose the details of blade failure investigations publicly. The authors have extensive experience with blade failure investigations and blade factory assessments; these activities provide insights into the critical aspects of adhesive bonds in blades. This paper presents the authors’ understanding of the causes of adhesive bond failures in blades, including failure modes and potential causal factors for blade bond failures, and provides perspectives on what it takes to consistently make good adhesive bonds (e.g., bonds that meet specifications and requirements) in blades.