PSI - Issue 18

Goran Vukelic et al. / Procedia Structural Integrity 18 (2019) 406–412 Vukelic, Pastorcic, Vizentin/ StructuralIntegrity Procedia 00 (2019) 000–000

409

4

2.2. Material Chemical composition of the gear material was determined using glow discharge spectrometer (GDS) LECO GDS500A, Tab. 1.

Table 1. Chemical composition of the gear material (w t %). C Mn Si P S Mo Ni

Cr

V

Rest

0.25

0.18

0.24

0.024

0.021

0.35

2.2

1.00

0.06

95.725

Composition of tested material is adequate to the special alloy structural steel 28NiCrMoV8-5. The alloy structural steels are widely used in automotive, plane and marine industry, guided missile, weapons, railway, bridges, pressure vessels, machine tools, mechanical components with a bigger sectional size, etc. It is a spring steel typically used in manufacturing of light and heavy vehicle leaf springs and coil springs, safety valve springs, shock absorbers on heavy machinery, instrument springs, friction plates, etc. Comparing the composition of the tested steel to standard EN 10250-3:2000, it can be noted that the percentage of nickel is just over the standard range (1.8-2.1 %), while chromium is just at the minimum value (1-1.5 %). As there was enough material, three standard tensile test specimens were machined out of shaft part and tensile test performed to determine material yield strength of 473 MPa, tensile strength of 820 MPa and Young modulus of 188 GPa. All of the values are within standard range for steel 28NiCrMoV8-5. 2.3. SEM analysis Fracture surfaces on the specimens cut from gears, Fig. 4, were examined using scanning electron microscope (SEM) FEI Quanta 250 under suitable magnification. Spalling damage can be detected along the damage area.

a)

b)

c)

Fig. 4. SEM of fractured spiral bevel gearat locations corresponding to Fig. 3: a) location 1a, 50x magnification, b) location 1b, 31x magnification, c) location 1c, 60x magnification. 3. Calculation Finite element (FE) model of considered gear pair was built in order to perform a numerical analysis of the stress and the contact pressure. Scanned dimensions of the gear pair were used to build 3D FE model of tetrahedron elements in Ansys, with mesh refinement of teeth and contact surfaces . In order to verify FE model, first, a stress analysis, according to DIN 3991[6], is performed. The gear ratio is 4, with pinion and gear number of teeth 17 and 68, respectively. The gear pair was loaded with 700 Nm on the output. Maximum equivalent stress obtained numerically