Issue34

E. Marcisz et alii, Frattura ed Integrità Strutturale, 34 (2015) 379-386; DOI: 10.3221/IGF-ESIS.34.42 380 Cu Mn Zn Mg Fe Cr Si Ti Al 4.40 0.62 0.08 1.70 0.25 0.01 0.13 0.05 Balance Table 1 : Chemical composition (in wt %) of the 2024 aluminium alloy  y (MPa)  u (MPa) E (GPa) A 5 (%) 432 552 77.5 12 Table 2 : Mechanical properties of the 2024 aluminium alloy Aluminium alloys containing copper and magnesium, that is duralumin, are among materials characterised by high strength properties. In the structure of a specimen cut off along the rod axis, are visible elongated grains of the  solid solution as well as numerous precipitations of the intermetallic phase CuAl 2 , Al 3 Mg 2 , Al 6 Mn containing iron Cu 2 FeAl arranged in a streaked way, mainly on the grain boundaries (Fig. 1). Precipitations of these phases significantly influence on strength and hardness of 2024 aluminium alloy. In particular, the precipitations in the phase boundaries decrease the plastic properties. Figure 1 : The 2024 aluminium alloy microstructure under magnification 500x Test pieces are square cross-section specimens taken from a bar 20 mm in diameter, shown in Fig. 2. Figure 2 : Shape and dimensions of specimen (in mm). The specimens have been tested on MZGS-100Ph fatigue test stand, shown in Fig. 3. The test stand enables conducting structural material test, subjected to bending, torsion or various combinations of sine bending-torsional loads. The test stand is composed of three sub-assemblies: the loading one, the driving one and the control and measurement one. The driving sub-assembly transmits its rotational speed from motor through the driving belt transmissions to the loading sub- assembly. The loading sub-assembly consists of vibrators loaded with weights, rods, levers and springs. Unbalanced