Abstract
Over the years, there has been an increased research interest on the use of adhesively bonded composite reinforcements for upgrading metallic structures. Although most of this work has concentrated on the use of composites for the fatigue repair of aircraft components (e.g. Baker & Jones 1988), recently, a small number of studies has focused on the use of bonded composite plates for strengthening metallic bridge members (e.g. Tavakkolizadeh & Saadatmanesh 2003a). However, the emphasis of this research has been on the strengthening of deteriorated or degraded steel members with only a handful of cases, where the strengthening of fatigue damaged steel bridge components was investigated (e.g. Tavakkolizadeh & Saadatmanesh 2003b). In this paper, the problem of a steel plate with a fatigue surface crack growing in the thickness direction, reinforced with an adhesively bonded composite (CFRP) patch is analysed using the finite element method. Parametric 2D finite element (FE) analyses are performed and the effect of a number of parameters, such as the crack depth and the properties of the patch and the adhesive on the interfacial shear and peel stress distributions, the crack tip stress fields and the fatigue life of the repaired plate is investigated. Results for the shear and peel stresses developed at the steel/adhesive interface indicate that severe stress concentrations occur at the extremities of the patch at the near-crack and end-of-patch positions. Greater peel stresses are found near the end-of-patch region, while the region near the crack is found to be dominated by large shear stresses. The shear stresses in the latter region are found to be several times greater than those near the end-of-patch region. The beneficial effects of crack patching are observed through the considerable reduction in the stress magnification factor Y. A parametric study whereby the Young's modulus and the thickness of the patch (Ec and tc) and the adhesive (Ea and ta), normalised by those of the steel plate (Es and ts), are varied in a systematic way, demonstrates that the reduction in Y is influenced primarily by the properties of the patch (see Fig. 1). Fatigue life calculations based on the crack growth model by Paris & Erdogan (1963) show a significant increase in the fatigue life of the damaged plate, when this is strengthened with a patch. This is shown in Table 1, where the ratio of the fatigue life for a patched plate Np to that for an unpatched plate Nu is presented for different patch configurations. Typically, the fatigue life is increased by approximately 2.6 to 3.6 times for cracks growing between 10% and 50% of the plate's thickness. Although these preliminary results appear to be encouraging they do not take into account debonding, which generally decreases the patch effectiveness. Further work in this direction is currently in progress. © 2006 Taylor & Francis Group.