Strengthening of old metallic structures in fatigue with prestressed and non-prestressed CFRP laminates

Test results and theoretical considerations on four different configurations of strengthened old steel plates with a centre notch loaded in fatigue are presented in this paper. The main interest of the research was to improve fatigue life by adhesive bonding of CFRP laminates on the steel surface, and this was achieved. Measurements included monitoring of crack growth and strains/stresses in the laminate and adhesive. Results showed that it was possible to lengthen the fatigue life almost four times as long as a reference specimen with non-prestressed laminates, and when prestressing laminates, crack growth was halted completely. A simple fracture mechanics solution was used to predict stop of crack growth for prestressed specimens, and a linear elastic model for stresses in the adherents and adhesive was used for design of the specimens. Both proved their reliability with well prepared and precisely fabricated specimens.