Fatigue performance of open-hole structural elements reinforced by CFRP overlays

The main aim of the study is to improve a strengthening procedure of structural elements, based on the application of CFRP overlays and adhesive joints, which allows for an increase in the fatigue life from low-cycle fatigue to at least a high-cycle fatigue regime. In experimental investigations, the effectiveness of three different adhesives is analysed which differ in chemical compositions and stiffness modulus (S&P Resin 220 Epoxy adhesive, 3 M Scotch-Weld DP6310NS, and Loctite HY 4080 GY). The experimental fatigue tests (stress ratio R = 0.1) are performed for flat specimens with a square hole with rounded corners reinforced by CFRP overlays. The maximal nominal tensile load is set close to the Yield limit. It is observed that fatigue strength mainly depends on the applied adhesives and the increase of fatigue strength of the reinforced sample varies in the range FI = 48%–1000 % with respect to the fatigue life of the bare sample. The highest efficiency of fatigue performance is reached for Loctite HY 4080 GY for which the average fatigue life increase is about FI = 890 %. •Application of CFRP overlays may significantly increase the fatigue life (even 10 times).•Properties of the adhesive layer have a significant influence on the fatigue strength.•Full-field surface strains and damage growth during fatigue tests can be determined with the use of Digital Image Correlation.•Application of adhesively bonded CFRP overlays reduces the stress concentrations.