Influence of the Notch Radius on Fatigue Crack Propagation in Beam Specimens of 2017A-T4 Alloy
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INFLUENCE OF THE NOTCH RADIUS ON FATIGUE CRACK PROPAGATION IN BEAM SPECIMENS OF 2017A-T4 ALLOY D. Rozumek1,2 and S. Faszynka1 We present experimental results on the fatigue crack growth in specimens with rectangular cross sections made of 2017A-T4 aluminum alloy under bending. The specimens were weakened by sharp and blunt one-sided notches (for the notch root ρ = 0.2; 5; 10 and 22.5 mm). The tests were performed on a MZGS-100 fatigue test bench in the low- and high-cycle fatigue modes by imposing a constant value of the nominal load ratio R = – 1; 0 and a moment amplitude M a = 15.84 N⋅m. The results of fatigue tests were then analyzed in terms of the parameter ΔK including the influence of the notch. Keywords: fatigue crack growth, notch, bending, stress intensity factor range.
The fatigue crack growth rate is directly related to the existing stress concentrators in the studied elements [1, 2]. The fatigue-crack initiation usually occurs at the notch root. In many cases, the shape of the notch affects the fatigue life and the fatigue crack-growth rate [3, 4]. In the paper [5], the author presents a model for the description of the fatigue crack-growth rate including the shape of the notch and crack length in the specimen. The proposed model correctly describes the fatigue crack-growth rates in the specimens and in the actual machine parts of various shapes and sizes. The paper reveals that the applied model also enables one to determine the critical crack length. The authors of the paper [6] established the influence of the notch and the stress ratio on the fatigue life within the scope of crack initiation and propagation for the 7075-T6 aluminum alloy. Two parameters were proposed to specify the maximum local stresses with the help of which it is possible to determine the initiation and propagation of fatigue cracks in the analyzed element. In paper [7], the authors obtained a solution of the plane problem of the theory of elasticity for a plane with semiinfinite rounded V-shaped notch subjected to antisymmetric loading. On this basis, the relations between the stress intensity factor at the vertex of a sharp V-shaped notch, the maximal stresses on the boundary contour or the stress gradient at the vertex of the corresponding rounded V-shaped notch, and its radius of rounding were established. The main aim of this paper is to characterize the fatigue crack-growth rates in terms of the parameter K taking into account the shape of the notch, by using experimental data obtained for the specimens with rectangular cross sections. Material, Properties, and Test Bench The tested material was 2017A-T4 aluminum alloy (Polish standard PN-EN 573-3: 2010), which belongs to the group of nonweldable, moderately workable, and cyclically hardening materials. This kind of materials is widely used in the aircraft and aerospace structures. 1 2
Opole University of Technology, Opole, Poland.
Corresponding author; e-mail: [email protected].
Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 53, No. 3, pp. 112–117, May–Jun
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