PSI - Issue 41

Liviu Daniel Pîrvulescu et al. / Procedia Structural Integrity 41 (2022) 492–499 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Material and methods Constant amplitude fatigue tests were performed on the AM 50A magnesium alloy at ambient temperature. Table 1 shows the chemical composition for the AM50 magnesium alloy (with aluminum as the main alloying element) used to make the steering armatures. Table 1. Chemical composition of AM50A alloy Name alloy Al Fe (max.) Mn Ni (max.) Zn AM50A 4.9 0.004 0.32 0.002 0.22 The magnesium alloy AM50A has high mechanical characteristics (mechanical strength, elongation, deformation energy absorption), the mechanical properties are highlighted in Table 2, Serban et al. (2019). Table 2. AM50A alloy mechanical properties Mechanical properties Density [g/cm 3 ] Yield strength [MPa] Tensile strength [GPa] Elongation [%] 15 Fatigue tests were performed on the 100 kN Walter Bai hydraulically operated machine. Two sets of circular specimens were tested, loaded with traction with sinusoidal cycle having the degree of asymmetry of the cycle = 0.1 and the frequency = 5 . The first set of tests consisted of specimens obtained by casting with an average diameter = 6.2 and the second set of tests consisted of specimens obtained by casting and then processed by cutting with an average diameter = 8.0 , Fig. 3. a b Fig.3. Circular test specimens: (a) = 6.2 ; (b) = 8.0 3. Results and discussion A total number of 7 specimens from each set were tested. The test results are shown in Fig. 4 as S-N fatigue curves corresponding to each set of samples tested (excluding specimens that were broken or showed major casting defects). The test were performed under similar conditions for the two sets of samples. The results indicate a major effect of section size on finite fatigue durability. The analysis of the fatigue curves in Fig. 4 shows that the fatigue strength decreases as the diameter of the test piece increases. Fatigue resistance for finite lifetime can be represented by a power law similar to Basquin's law: = ′ ∙ ( ) (1) where is the stress amplitude, ′ is the fatigue strength coefficient, is the finite number of cycles and is the slope of the fatigue curve. Modulus of elasticity [GPa] AM50A 1.77 45 125 230