PSI - Issue 47

Aleksandr Inozemtsev et al. / Procedia Structural Integrity 47 (2023) 705–710 Author name / Structural Integrity Procedia 00 (2019) 000–000

707

3

Nomenclature N

number of cycles applied stress



scale related to the correlated behaviour in the ensemble of defects

l sc

scale associated with the process zone

L pz

correlation function

K(r)

Hurst exponent (surface roughness index)

H

surface relief height

z(x)

window of size

r

2. Materials and experimental conditions The low-cycle fatigue tests were performed for specimens cut from a plate of titanium alloy Ti-6Al-4V in the longitudinal and transverse directions. The schematic diagram of the specimen is shown in Figure 1.

Fig. 1. Geometry of the specimen used in low-cycle fatigue test, the dimensions are in mm.

The chemical composition (in weight %) of the alloy is shown in Table 1 and its tensile properties are summarized in Table 2. Table 1. Chemical composition of Ti-6Al-4V grade (in weight %). Al V Zr Si  Fe C O N H 6.6 4.3 0.021 0.026 0.21 0.009 0.175 0.002 0.0022

Table 2. Quasi-static tensile characteristics of Ti-6Al-4V grade. Elastic modulus (GPa) Yield stress (MPa)

Tensile strength (MPa)

Ultimate elongation (%)

115

814

950

16

Low-cycle fatigue tests in a soft cycle loading mode with a dwell period of 2, 5, 10 and 20 minutes in the loading cycle were conducted in accordance with ASTM E606 within the operating time up to 10000 cycles at room temperature for the asymmetry coefficient Rσ=0. The low-cycle fatigue characteristics were studied using the LFMZ test machine. The validity of theoretical assumptions about the leading role of multiscale mechanisms of structural relaxation caused by the collective behavior of the ensembles of defects, and the development of localization of plastic flow and fracture was investigated by the methods of structural analysis of the surface relief morphology using the optical interferometer-profiler NewView-5010. The obtained data were then used to calculate the scale invariant (the Hurst exponent) and the spatial scale of the region exhibiting the correlated behavior of microshears. The evaluation of the Hurst index of deformation structures can provide the physically meaningful interpretation of the universal nature of