A practical approach to fracture analysis at the trailing edge of wind turbine rotor blades

Abstract

Wind turbine rotor blades are commonly manufactured from composite materials by a moulding process. Typically, the wind turbine blade is produced in two halves, which are eventually adhesively joined along their edges. Investigations of operating wind turbine blades show that debonding of the trailing edge joint is a common failure type, and information on specific reasons is scarce. This paper is concerned with the estimation of the strain energy release rates (SERRs) in trailing edges of wind turbine blades in order to gain insight into the driving failure mechanisms. A method based on the virtual crack closure technique (VCCT) is proposed, which can be used to identify critical areas in the adhesive joint of a trailing edge. The paper gives an overview of methods applicable for fracture cases comprising non‐parallel crack faces in the realm of linear fracture mechanics. Furthermore, the VCCT is discussed in detail and validated against numerical analyses in 2D and 3D. Finally, the SERR of a typical blade section subjected to various loading conditions is investigated and assessed in order to identify potential design drivers for trailing edge details. Analysis of the blade section model suggests that mode III action is governing and accordingly that flapwise shear and torsion are the most important load cases.Copyright © 2013 John Wiley & Sons, Ltd.

Measurement of local relative displacements in large structures

“…Moreover, a greater number of measurements would be required to decrease uncertainties. The measured Mode-III deformations as discussed in [5] were too small in this case to serve for comparison purposes. On the other hand, the applied shear force was comparatively low, leading to low out-of-plane shear displacements.…”

Effects of geometric non-linearity on energy release rates in a realistic wind turbine blade cross section

“…Note that the influence of Mode-III was not dealt with in this paper. On the other hand, the shear force and torsional moment magnitude -both of which contribute strongly to Mode-III as described in [22] -are considered to be low in the investigated cross-section, as they are far from the root. Nevertheless, future fracture analyses of adhesive joints should include the effects of shear and torsion.…”

“…ijkl show that if all components of σ kl except σ xz are zero then ϵ 22 and ϵ 33 ̸ = 0. Therefore, the in-plane warping deformations do not -strictly speaking -comply with the adopted boundary conditions for torsion.…”

Prospective challenges in the experimentation of the rain erosion on the leading edge of wind turbine blades

“…The damage should be understood as changes to the constitutive material and/or the geometric properties, including alterations to the boundary conditions and structural connectivity, which can adversely affect structural and power performance . Thus, several issues have been studied, eg, manufacturing process, fracture, fatigue, and adhesive joints . Although diverse turbine designs exist, currently the most common design is built in an upwind horizontal axis with three blades.…”