Issue 42

D. Rozumek et alii, Frattura ed Integrità Strutturale, 42 (2017) 23-29; DOI: 10.3221/IGF-ESIS.42.03 24 E XPERIMENTAL PROCEDURE Material and specimen pecimens with rectangular cross-section and gross size 8 x 10 mm were used in fatigue tests. The specimens were made of the AW-2017A-T4 aluminium alloy and described in the standard PN-EN 573 of 1997. Mechanical properties of the material are given in Tab. 1. The specimens were made of a extruded bar 16 mm in diameter.  y (MPa)  u (MPa) E (GPa)  382 480 72 0.32 Table 1 : Mechanical properties of the AW-2017A-T4 aluminum alloy. The specimens had an external, unilateral notch, which was a 0 = 2 mm long and its radius was  = 0.2 mm (Fig. 1). The notches in the specimens were cut with a milling cutter and their surfaces were polished on abrasive paper with decreasing gradation. The theoretical stress concentration factor in the specimen under bending K t = 3.76 was estimated according to Ref. [14]. Figure 1 : Shape and dimensions of specimen (in mm). Alloys of aluminium with copper and magnesium, that is duralumin, belong to alloys characterised by supreme strength properties. Elements of such shape are used, among others, in cars (by Renault Co.), trucks and tanks (attaching springs) as torsion bars, and as indirect beams used in drilling for oil and natural gas. Fig. 2 shows a microstructure of the AW- 2017A-T4 aluminium alloy. The microstructure heavily dominated by elongated grains of the solid solution α of various sizes, and a width of about 50 μm. Between large elongated grains are also visible cluster very small equiaxed α phase grains in the system band. On a background of solid solution α, there are many precipitation of intermetallic phases, particularly Al 2 Cu, as well as Mg 2 Si, AlCuMg. Precipitations phase Al 2 Cu occur mainly in the chain system on grain boundaries of the solid solution, and their size does not exceed 5 mm [15]. Figure 2 : Microstructure of the AW-2017A-T4 aluminum alloy. S