This paper presents a study involving the assessment of strength of bonded joints. Coupon specimens made of 6061-T6 aluminum alloy were used in the fatigue strength testing experiments. Two sharp grooves were cut on each face of the specimen in order to simulate the cracks in the wind turbine blade. Thin patches made of the same material were adhesively bonded to the surface of the specimen, covering the grooves. All coupon specimens with and without patches were tested under oscillating bending load. Parameters such as the thickness of the adhesive material, the peeling strength and stress distribution between layers were investigated. Failures in the form of patch delamination and subsequent structure fracture were recorded and the numbers of loading cycles which caused these failures were determined. Relationships between the applied loads and the fatigue lives of tested specimens were established. On the basis of the experiments and Finite Element Analysis, an easy-to-use method for estimating the fatigue life of a real wind turbine blade was developed. The proposed method can be extended to applications involving patching of other structures subjected to repeated loads.
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