FRACTURE OF STRUCTURAL ADHESIVE UNDER PURE MODE III LOADING CONDITIONS: EXPERIMENTAL STUDY AND CHALLENGES

As one of the primary load-carrying materials, adhesives play a crucial role in the structural integrity of composite-made wind turbine blades. A thorough understanding of the mechanical behavior of adhesives in terms of fracture behavior is mandatory in order to optimize the blade design. Fracture analysis of trailing edge failure revealed that mode III contributed the most to the strain energy release rate, with flapwise shear and torsion being the principal load cases responsible for mode III fracture. According to the authors' knowledge, there are few publications that investigate the fracture behavior of bulk adhesive in pure mode III. In order to evaluate the fracture behavior of bulk adhesives under pure mode III loading conditions, Single Edge Notch (SEN) specimens were utilized in this investigation. SEN specimens were selected because it is impossible to produce cylindrical specimens with high viscosity adhesive, which is prevalent in the wind turbine sector. The specimen was loaded under out-of-plane shear at the fracture plane using one of the available test rigs, i.e., asymmetric four-point bending. Acoustic Emission (AE) has been employed to assess the position of damage onset during the test since the specimens break from the crack plane and inner support. By AE localization, it has been demonstrated that the majority of AE events and resulting damage are concentrated on the crack plane and that the ultimate fracture occurs at the crack tip.

Keywords:fracture, mode III, adhesive, wind turbine blades