PSI - Issue 5

Valeriy Lepov et al. / Procedia Structural Integrity 5 (2017) 777–784 Valeriy L pov et al. / Structural Integrity Procedia 00 (2017) 00 – 000

779 3

STM-, ASM- and optical microscopy and fractography of deformation and fracture surfaces

Size distribution of microdefects on different structural levels

1 mkm

Fractal parameters of damage

Estimation the limit size of parameters

Stochastic modeling of growth and branching of small crack

Damage accumulation law

Coherent model of elastoplasticity

Statistical regularity of fracture

and damage accumulation

Estimation of limit state and lifetime of structure element or construction

B

A

Fig. 1. (a) Scheme of assessment of the strength and lifetime on the basis of structural modeling; (b) STM-image of deformation surface of steel probe with grain boundary and inhomogeneities.

2.2. Materials and method for mechanical tests The locomotive tires are exposed to influence of various loadings during operation. Material of the wheel of this locomotive element is merged in the complex stress state. So the internal and superficial defects are developed and damage plastic deformation and difficult tension takes place. The standard tension test for the steel does not a great gulf fixed for mechanical properties (as yielding, breaking point, and tensile strain) at room and low temperature (see Table 1). But because the bandage of locomotive tire is operated not only in a wide range of working temperatures, but in static and dynamic loading too the principle is to study the impact toughness of the material of the band, as positive (20  C) and below freezing (-20, -40, -60  C) also. Table 2 shows the results of impact test of bandage steel and average values for three or five samples. For welded steel probes the 30 run were carried out during the arc welding process, and a total of four different beads were achieved, such as the root run, hot pass, the filling and the capping. But before these welding runs were made, the steel alloy of 8 mm thickness was cut into the required dimension with the help of lathe machine. The initial joint configuration was obtained by securing the plates in position using tack welding. Single V butt joint configuration was used to fabricate the joints using manual metal arc welding process. This welding was done on the both side of the material. All the necessary cares were taken to avoid the joint distortion and the joints were made with applying clamping fixtures. The specimens for testing were sectioned to the required sizes.