Mixed mode I/II fatigue crack arrest in steel members using prestressed CFRP reinforcement

Abstract

In the present study, a strengthening design approach is proposed for the mixed mode I/II fatigue crack arrest in existing structural steel members using prestressed unbonded carbon fiber reinforced polymer (CFRP) composites. Through the analytical formulation of mode I and II stress intensity factor ranges, a design model is proposed to determine the strengthening solution, including the required prestressing level and/or the cross-sectional area of the reinforcement, which would ensure the complete arrest of an existing mixed mode I/II fatigue crack in a steel member. In parallel, sets of stepwise high-cycle fatigue tests were carried out on reference unstrengthened and prestressed CFRP-strengthened precracked steel plates of grade S355J2+N under various mode mixities. The experimental results revealed that the maximum tangential stress (MTS) criterion fairly predicts the state of the mixed mode I/II fatigue cracks (i.e., crack arrest or growth) in unstrengthened specimens, while the proposed design model provides a conservative estimation of the mixed mode I/II fatigue threshold in prestressed CFRP-strengthened specimens. Furthermore, the crack propagation characteristics of grade S355J2+N steel, i.e., Paris' law parameters (C and m) and the crack closure parameter (U), were determined and demonstrated to be independent of the material rolling direction. Based on the analytical and experimental results of the current study, it can be concluded that the proposed model can be used for the safe design of strengthening solutions, which is an increasing need to extend the service life of existing fatigue-damaged steel structures; certain recommendations are provided in this regard for practical strengthening applications.

Irreversible cyclic cohesive zone model for prediction of mode I fatigue crack growth in CFRP-strengthened steel plates

“…Note that the above results were not confirmed by the experimental study in [18] where it was shown that the mode mixity also plays a role on the fatigue lifetime. Fatigue crack growth in CFRP repaired four-point bend specimens was investigated in [10].…”

“…This technique was successfully applied to strengthen old steel bridges in Switzerland [3] and in Australia [4]. In all the above-mentioned studies, emphasis was on preventing crack initiation or on promoting crack arrest under both mode I [17] and mixed mode I/II [18] loading condition, resulting in the fatigue lifetime extension of old fatigue-sensitive steel structures. They proposed, through some conservative assumptions, suitable models to achieve a practical estimation of the fatigue crack threshold and the required prestressing level in the strengthening systems for crack arrest.…”

Iron-based shape memory alloy (Fe-SMA) for fatigue strengthening of cracked steel bridge connections

“…Nevertheless, with some further crack propagation and with the presence of shear stresses, the combined effects of bending and shear stresses govern the crack scenario. However, the mechanisms for crack propagation is still based on maximum principal stress [58]. The fatigue crack growth is resolved by the mode-I stress intensity factor (SIF) range, ∆K I = K I,max − K I,min , at the tip of the crack during the early stages of propagation.…”

Stress Intensity Factor Assessment for the Reinforcement of Cracked Steel Plates Using Prestressed or Non-Prestressed Adhesively Bonded CFRP

“…Adding pre-stressing force in the CFRP material allows using a more significant portion of the strength of the material. Moreover, by applying an adequate level of pre-stress to the CFRP laminate, the effective SIF at crack tip can be reduced below the SIF threshold and therefore lead to a full stop of the crack propagation [ 11 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ].…”