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Crack behaviour after High Frequency Mechanical Impact treatment in welded S355 structural steel
Published in Hiroshi Yokota, Dan M. Frangopol, Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations, 2021
H. Al-Karawi, M. Al-Emrani, J. Hedegård
It was stated in section 1 that the flow of material behind the crack tip is the main cause of plasticity-induced crack closure. That implies that the HFMI’s capability of closing the cracks depends on the position of impact with respect to the crack. In light of that, several FE-simulations were conducted on a 1 mm cracked structure where the position of impact was changed in each model. The results showed that the treatment should always be slanted toward the base metal. Otherwise, the cold working might cause material flow away from the crack which has a detrimental effect and caused additional crack opening. Figure 15 summarizes the findings. The Figure shows the crack closure shape for each impact position. Notice that case (2) shown in the Figure is similar to the finding in Figure 4 which witnessed full crack ‘‘disappearance’’. That emphasizes the importance of controlling the position of impact when HiFIT is to be used for crack retrofitting.
Fatigue Crack Growth under Large-Scale Plasticity
Published in Ashok Saxena, Advanced Fracture Mechanics and Structural Integrity, 2019
Crack closure is a phenomenon by which the crack surfaces close at the crack tip prior to the external load or stress becoming zero during the fatigue cycle. The portion of the loading cycle after crack closure is ineffective in growing the crack and thus the corresponding load range must be subtracted from the applied cyclic load, ΔP, to determine the value of the loading parameter such as ΔK. This phenomenon was first observed by Elber [11,12] who argued that a zone of residual tensile deformation is left in the wake of a growing fatigue crack. The residual deformation causes the opposing fracture surfaces in the crack vicinity to come in contact, prior to the completion of unloading. The load at which the opposing crack surfaces first come in contact is called the crack closure load. Similarly, upon reloading, the crack tip remains at least partially closed until a load equal to the crack opening load is applied. Thus, the region ahead of the crack tip remains at a lower stress until the load exceeds the crack opening load. The crack opening and closing loads are nearly identical. This type of crack closure is referred to as the plasticity-induced crack closure in the literature.
Fatigue Crack Propagation
Published in T.L. Anderson, Fracture Mechanics, 2017
Interferometric techniques provide a local measurement of crack closure [57]. Monochromatic light from a laser is scattered off of the two indentations on either side of the crack. The two scattered beams interfere constructively and destructively, resulting in fringe patterns. The fringes change as the indentations move apart.
Micromechanisms of a macrocrack propagation behavior affected by short to long fatigue microcracks
Published in Mechanics of Advanced Materials and Structures, 2022
Xu Li, Yue Sheng, Hongda Yang, Xiaoyu Jiang
Crack closure effect is mainly determined by the residual plasticity at the crack tip. Under the constant amplitude fatigue load, the size of residual PZ at the crack tip is a quarter of the area of maximum PZ. Thus, when the load exceeds the residual plasticity stresses, or the load is half of the maximum load, the Kop and U can be described as Kop = 0.5·KI, max and U = 0.5, respectively. In this article, the material is considered as ideal elastoplastic, the external load is proportional loading-unloading cycle, the stress ratio R = 0. When Kop decreases and U increases, the plastic hardening effect may be occurring and the size of residual PZ is very small. Elber [37] developed the U for aluminum alloy by means of experiment, the U is described as U = 0.5 + 0.33R + 0.12R2. In the equation, the stress ratio R is a function of U, and the plastic hardening effect of materials is considered automatically. With regard to aluminum alloy, when R = 0, the U = 0.5.
Fretting fatigue behaviour of Ti–6Al–4V in contact with Alloy 718
Published in Tribology - Materials, Surfaces & Interfaces, 2022
S. Srivathsan, S. Ganesh Sundara Raman
There have been studies dealing with the effect of contact pressure on fretting fatigue life, e.g. see Ref. 5–7. Fernando et al. [5] reported the effect of contact pressure on fretting fatigue life of BS L65 4% Cu–Al alloy. At low contact pressures, fretting fatigue life decreased with an increase in contact pressure, the usual trend. However, at high contact pressures life increased with an increase in contact pressure. It was attributed to the retardation of crack growth produced by crack closure due to the high compressive contact load. Nakazawa et al. [6] reported a monotonous reduction in fretting fatigue life for a high strength steel and a titanium alloy with an increase in contact pressure at higher cyclic stress amplitudes. However, at lower cyclic stress amplitudes the variation of fretting fatigue life with contact pressure exhibited a variable behaviour, i.e. minimum life at a low contact pressure, maximum life at an intermediate contact pressure, then life decreased again and became constant at high contact pressures. This behaviour was explained on the basis of change in frictional stress, critical relative slip, crack growth retardation effect due to crack closure at high contact pressures and stress concentration effect. A similar behaviour was observed in Al–Mg–Si alloy AA6061 [7].
Optimization of a cruciform specimen for fatigue crack growth under in and out-of-phase in-plane biaxial loading conditions
Published in Mechanics of Advanced Materials and Structures, 2023
R. Baptista, V. Infante, J. F. A. Madeira
For in-phase loads, three different biaxial load ratios were applied (Table 5). The stress ratio was considered to be equal to 0.1. Although the introduced mean stress will affect the final fatigue life, crack closure effects are reduced.