TY - JOUR

T1 - Mixed mode I/II fatigue crack arrest in steel members using prestressed CFRP reinforcement

AU - Hosseini, Ardalan

AU - Nussbaumer, Alain

AU - Motavalli, Masoud

AU - Zhao, Xiao Ling

AU - Ghafoori, Elyas

N1 - Funding Information: The authors gratefully acknowledge the financial support provided by the Swiss National Science Foundation (SNSF) Project No. 200021-153609 , and the Australian Research Council (ARC) Linkage Grant ( LP140100543 ). The first author would like to sincerely thank Walter Bollier, Alex Stutz, Roland Koller, and Hans Michel from the Mechanical Systems Engineering Laboratory, as well as the technicians of the Structural Engineering Research Laboratory of Empa, for their exceptional support and assistance in performing the experiments. Furthermore, the technical support provided by the Central Workshop of Empa in manufacturing the specimens and mechanical components is highly acknowledged. Finally, special thanks go to S&P Clever Reinforcement Company AG, Switzerland, for providing the materials that were used in the experiments. Publisher Copyright: © 2019 Elsevier Ltd

PY - 2019/10

Y1 - 2019/10

N2 - 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.

AB - 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.

KW - Carbon fiber reinforced polymer

KW - Crack arrest

KW - Design model

KW - High-cycle fatigue testing

KW - Mild steel

KW - Mixed mode I/II loading

KW - Prestressed strengthening

KW - Steel structures

UR - http://www.scopus.com/inward/record.url?scp=85067996661&partnerID=8YFLogxK

U2 - 10.1016/j.ijfatigue.2019.06.020

DO - 10.1016/j.ijfatigue.2019.06.020

M3 - Article

AN - SCOPUS:85067996661

VL - 127

SP - 345

EP - 361

JO - International journal of fatigue

JF - International journal of fatigue

SN - 0142-1123

ER -