Debonding in FRP strengthened beams: Stress assessment versus fracture mechanics approach

In the present paper we analyze the debonding failure of abeam strengthened by a fiber reinforced polymer. We propose an analytical approach, whose basic assumptions are that (i) sections inside the beam remain plane and (ii) the adhesive layer acts as a shear lag. A stress concentration is found at the edge of the reinforcement length. Two failure criteria are proposed to study the debonding process. The former is a stress assessment criterion, i.e. failure takes place whenever the maximum tangential stress reaches a limit value (the interfacial bond strength). The latter is an energy, fracture mechanics criterion, i.e. failure takes place as long as the strain energy release rate due to debonding reaches a critical value (the interfacial fracture energy). By means of Castigliano's theorem, the load vs. deflection graph is drawn, showing the possible rising of both snap-back and snap-through instabilities.