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Fatigue crack growth under overload/underload in different strength structural steels
Abstract Aiming at the different strength-level structural steels, fatigue crack growth rate (FCGR) tests were conducted under a series of loading conditions, i.e., constant amplitude load (CAL), single overload (OL), single underload (UL), or periodic underloads (PULs). Meanwhile, the effects of various baseline loading stress ratios on the FCGR were considered. To analyze the effects of crack-tip behavior on the crack propagation following an OL/UL, the crack-tip strain fields and crack opening displacement were obtained by digital image correlation (DIC). It was found that when the OL/UL-amplitude was constant, the fatigue crack propagations under the OL/UL were affected by both steel strengths and baseline loading stress ratios. In general, an increase in the steel strength grade indicated a lower crack retardation/acceleration during the OL/UL process, which was more evident under the lower baseline stress-ratio condition. The higher the strength, the lower the crack-opening stress level, the smaller the plastic zone size, and the higher the crack-tip residual strain. Correspondingly, there were different variations in the instantaneous FCGR and OL/UL-affected cycles. When the OL/ULs are considered in the design stage, our work can guide the steel strength grade selection and provide a better understanding of the crack growth retardation/ acceleration mechanisms.
Highlights Fatigue crack growth rates in the structural steels with strength grades of 355, 460, 550, and 690 MPa were focused. The crack growth retardation/acceleration caused by overload/underload in various steels was systematically investigated. The structural steel strength effect on the crack growth retardation and acceleration was summarized. Crack-tip deformation that followed the overload/underload was observed through DIC, XRD, TEM and calculated by FEA. Mechanisms of the crack growth retardation and acceleration that occurred in the structural steels were discussed.
Fatigue crack growth under overload/underload in different strength structural steels
Abstract Aiming at the different strength-level structural steels, fatigue crack growth rate (FCGR) tests were conducted under a series of loading conditions, i.e., constant amplitude load (CAL), single overload (OL), single underload (UL), or periodic underloads (PULs). Meanwhile, the effects of various baseline loading stress ratios on the FCGR were considered. To analyze the effects of crack-tip behavior on the crack propagation following an OL/UL, the crack-tip strain fields and crack opening displacement were obtained by digital image correlation (DIC). It was found that when the OL/UL-amplitude was constant, the fatigue crack propagations under the OL/UL were affected by both steel strengths and baseline loading stress ratios. In general, an increase in the steel strength grade indicated a lower crack retardation/acceleration during the OL/UL process, which was more evident under the lower baseline stress-ratio condition. The higher the strength, the lower the crack-opening stress level, the smaller the plastic zone size, and the higher the crack-tip residual strain. Correspondingly, there were different variations in the instantaneous FCGR and OL/UL-affected cycles. When the OL/ULs are considered in the design stage, our work can guide the steel strength grade selection and provide a better understanding of the crack growth retardation/ acceleration mechanisms.
Highlights Fatigue crack growth rates in the structural steels with strength grades of 355, 460, 550, and 690 MPa were focused. The crack growth retardation/acceleration caused by overload/underload in various steels was systematically investigated. The structural steel strength effect on the crack growth retardation and acceleration was summarized. Crack-tip deformation that followed the overload/underload was observed through DIC, XRD, TEM and calculated by FEA. Mechanisms of the crack growth retardation and acceleration that occurred in the structural steels were discussed.
Fatigue crack growth under overload/underload in different strength structural steels
Liang, Hang (Autor:in) / Zhan, Rui (Autor:in) / Wang, Dongpo (Autor:in) / Deng, Caiyan (Autor:in) / Guo, Baichen (Autor:in) / Xu, Xiaohan (Autor:in)
26.02.2022
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
Structural steels , Fatigue crack growth , Overload , Underload , Crack-tip deformation , VAL , variable amplitude load , CAL , constant amplitude loading , OL , single overload , UL , single underload , FCGR , fatigue crack growth rate , LD , longitudinal (rolling) direction of the plate , TD , transverse direction of the plate , SIF , stress intensity factor , MT , central crack tension , PULs , periodic underloads , DIC , digital image correlation , FCG , fatigue crack growth , FEA , finite element analysis
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