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The fatigue crack behavior of 7N01-T6 aluminum alloy in different particle environments

Chen Y. Q., Tang Z. H., Pan S. P., Liu W. H., Song Y. F., Zhu B. W., Liu Y., Wen Z. L.

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 4

468--483

EN

An experimental method of evaluating the fatigue behavior of alloys in different particle environments was designed, and the effects of four kinds of particles (i.e., graphite, CaO, Al2O3, and MnO2) on the crack propagating behavior of 7N01-T6 behaviour alloys were investigated. The results show that the particles deposited on the crack surface exert significant influence on the fatigue crack propagation behavior thereof. This influence strongly depends on the elastic moduli of the particles (Ep). As Ep is less than that of aluminium alloy (EAl), the particle accelerates the fatigue-crack-growth rate (FCGR) in the alloys due to the lubrication of the particles on the mating fracture surfaces. When the difference between Ep and EAl is small, the particle effect on the FCGRs of the alloys is small due to the counteraction between the decrease in friction and the promotion on the crack closure of mating fracture surfaces. When Ep is greater than EAl, the particles slow down the FCGRs of the alloys on account of significant crack closure effect. As Ep is much greater than EAl, the particles increase the FCGRs because of the increasing stress concentration at the crack tip.

2

Effect of grain size on the fatigue crack growth behavior of 2524-T3 aluminum alloy

Shou W. B., Yi D. Q., Liu H. Q., Tang C., Shen F. H., Wang B.

Archives of Civil and Mechanical Engineering

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2016

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Vol. 16, no. 3

304--312

EN

2524-T3 aluminum alloy sheets with different grain sizes (13 μm, 59 μm, 178 μm, 355 μm, 126 μm, and 87 μm) were prepared using methods such as rolling and annealing. The microstructures and mechanical properties of the 2524-T3 aluminum alloy sheets were studied using optical microscopy (OM), scanning electron microscopy (SEM), and tensile and fatigue crack growth (FCG) rate tests. The grain size had a significant effect on the fatigue crack growth (FCG) rate. Alloys with grain sizes between 50 and 100 μm exhibited high fatigue crack propagation resistances and the lowest FCG rates (da/dN = 1.05–1.45 × 10−3 mm/cycle at ΔK = 30 MPa m1/2). Microstructural observations revealed that fatigue cracks propagated more tortuously in the alloy with grain sizes within the range of 50–100 μm. This result is attributed to the combined effects of grain boundaries, crack deflection, fracture surface roughness-induced crack closure, and plasticity-induced crack closure.

3

3D fracture mechanics investigation on surface fatigue crack propagation

Shen H., Guo W., Lu G.

International Journal of Applied Mechanics and Engineering

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2009

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Vol. 14, no 4

1127-1138

EN

Surface fatigue crack propagation is the typical failure mode of engineering structures. In this study the experiment on surface fatigue crack propagation in 15 MnVN steel plate is carried out and the crack-shape and propagation life are obtained. With the concept of "equivalent thickness" brought into the latest 3D (three dimensional) fracture mechanics theory, one closure model applicable to 3D fatigue crack is put forward. By using the above 3D crack-closure model, the shape and propagation life of surface fatigue crack in 15 MnVN plates are predicted. The simulative results show that the 3D fracture mechanics based closure model for 3D fatigue crack is effective.

4

Determination of crack closure for structural steel from local compliance records.

Skorupa M., Skorupa A., Machniewicz T.

Archive of Mechanical Engineering

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2004

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Vol. LI, nr 3

391-414

EN

The usefulness of elastic compliance measurements to estimate crack closure in structural steel and for validity of the assumption of a constant compliance value for the fully open crack is examined. Based on considering different issues related to the experimental technique and compliance data processing, local compliance measurements and the compliance offset method recomended by the ASTM standard are selected to be most suitable for structural steel. The compliance data generated in fatigue tests on 18G2A steel conducted under a variety of loading conditions enabled to choose optimal strain gauge positioning and appropriate offset criterion values for the orginal compliance offset method and its modified (normalized) version. The adequacy of the closure measurements is assessed through checking the ability of the resulting effective stress intensity factors to account for the observed effects of the loading conditions on fatigue crack growth rates.

PL

W artykule rozważono możliwość oszacowania poziomu zamykania się pęknięcia w stali konstrukcyjnej na podstawie pomiaru podatności spężystej z wykorzystaniem procedur opartych na konwencjonalnym założeniu, że podatność próbki z otwartym w pełni pęknięciem jest stała. Spośród możliwych do zastosowania technik pomiarowych i koncepcji wyznaczania poziomu otwarcia pęknięcia za najodpowiedniejszą uznano metodę zalecaną przez normę ASTM, której przydatność w zastosowaniu do stali konstrukcyjnej nie została dotąd sprawdzona. Dane podatności, zarejestrowane w trakcie badań zmęczeniowych stali 18G2A, prowadzonych przy różnych typach obciążenia, pozwoliły na zbadanie wpływu techniki pomiarowej i wartości przyjmowanych w metodzie ASTM kryteriów do oceny zamykania się pęknięcia. Adekwatność zastosowanych opcji pomiarowych i procedur obliczeniowych zbadano rozważając korelacje pomiędzy wynikami pomiarów zamykania się pęknięcia i zaobserwowanymi prędkościami wzrostu pęknięć.