Analysis of cracked steel members reinforced by pre‐stress composite patch

Abstract

Pre-stress bonded composite patch is a promising technique to reinforce steel member damaged by fatigue. ifhe effectiveness of this technique was verified by fatigue tests on notched steel plâtes. Results showed that the application of carbon fibre reinforced plastic (CFRP) strips and, eventually, the introduction of a compressive stress by pretension of the CFRP strips prior to bonding produced a significant increment of the remaining fatigue life. In this paper, the stress intensiqr factor in the notched plates is computed by a two-dimensional finite element model in connection with the three-layer technique in order to reduce the computational effort. Due to high stress concentrâflon at the plate crack tip, debond is assumed at the adhesive-plate interface. The goal is to illustrate the influence of some reinforcement parâmeters such as the composite strip stiffness, the pre-stress level, the adhesive layer thickness and the size of the debonded region on the effectiveness of the composite patch reinforcement.Keyvords composite patch; fatigue crack reinforcement; parametric analysis.In Bassetti5 a novel technique was proposed to reinforce steel member damaged by fatigue. It consists in the appiication of carbon fibre reinforced plastic (CFRP) strips and, eventually, the introduction of a compressive stress by pretension of CFRP strips prior to bonding. Note that this new methodology applied to riveted steel members avoids the drawbacks of standard reinforcement techniques such as hole drilled at crack fiont, cover plates application, replacement of rivets by high strength bolts, cold expansion of the rivet hole and welding of the detected cracks. effectiveness of pre-stress CFRP-strips to stop fatigue crack emanating from the rivet hole or to prevent further cracking at other locations. The carbon fibre reinforced plastic laminates have physical and mechanical properties particularly interesting for reinforcement of fatigue damaged steel elements. The high fatigue resistance of CFRP avoids crack propâ-gation from the cracked steel section into the patch. The high stiffness of CFRP reduces the stress range in the cracked steel section and promotes crack bridging. llhe high tensile strength of CFRP allows also the application of a pretension to composite strips in order to increase the effectiveness of the bonded patch on thicker steel section. Finally, the low self-weight of CFRP plates limits the dead load increment and simplifies the strengthening operations. Composite patch reinforcement technique is a standard and reliable procedure in different engineering branches to reinforce structural elements subjected to extreme actions (high fatigue loads, high temperature ranges and exposure to aggressive agents) and nowadays, is also a standard reinforcement methodology in aircraft industries.T In fact the CFRP laminates is becoming a familiar procedure for O 2003 B ackwe I Publ sh ng Ltd. Fatigue Fract Engng Mater Struct 26, 59-66

Fatigue crack growth in CFRP-strengthened steel plates

“…In several studies, the fatigue behavior of notched steel members reinforced by using prestressed CFRP laminates is considered. Prestressed reinforcements were observed to be more effective in extending the crack growth life [11,17,18]. Crack patching by prestressed CFRP strips produces, in fact, supplementary benefits since the compressive stresses introduced by prestressing the steel elements give rise to an additional reduction of the COD and emphasize the crack closure phenomenon.…”

“…The effects of one or two side reinforcements and of an application prior or subsequent to crack propagation were also taken into account. Colombi et al [11] showed that the application of pre-stress bonded composite patches is a promising technique to reinforce notched steel plates damaged by fatigue. The application of CFRP strips and, eventually, the pretension of the strips prior to bonding remarkably increased the remaining fatigue life.…”

Modelling fatigue crack propagation of a cracked metallic member reinforced by composite patches

“…This approach has already become a standard one in the aircraft industry [1], where most studies have focused on repair of cracked aluminum alloy structures [2][3][4][5]. Such applications have also been used in other engineering fields, such as automobile industry and civil engineering [6][7][8]. Most of the industrial members are subjected to fatigue loading.…”

“…Most of the industrial members are subjected to fatigue loading. Therefore, fatigue assessment has been widely applied to check the effectiveness of a composite patch [7][8][9][10][11].…”

Fatigue Behaviour of CFRP Strengthened Out-of-Plane Gusset Welded Joints with Double Cracks

“…Figure 13a illustrates a typical finite element model (double-sided strengthened specimen, a = 20 mm). A previous study [54] confirmed that local debonding existed around the crack tip area due to high stress concentration. Therefore, a semi-elliptical shaped debonding area was assumed at the adhesive-steel interface for the cases where the crack had propagated underneath the CFRP laminate, as shown in Figure 14.…”