PSI - Issue 36

G. Pysarenko et al. / Procedia Structural Integrity 36 (2022) 30–35 Pysarenko G., Voynalovich O., Maylo A. et al. / Structural Integrity Procedia 00 (2021) 000 – 000

31

2

structure, Yakovleva (2003). Elastic and plastic materials are characterized by localization of plastic deformation in the form of stable slip bands and other similar defects, Babinský et al. (2021) and Shanthraj et al. (2011) which characterize the measure of accumulated microplastic deformation initiating the destruction of a structural element. Under conditions of periodic deformation, there is deformation defects structure on its surface. The distribution function of discrete surface defects exhibits normal distribution properties due to random nature of shear localization in a polycrystalline structure slip planes of the deformed specimen surface, Seidametova et al. (2018). Plastic shifts of polycrystalline planes appear as a system of extrusions and intrusions, Mughrabi (2009). Sliding bands form a deformation relief of the deformed sample surface due to the process of multiple sliding in crystallographic planes of the material surface layer. The accumulated defects relief depth (intrusions) of a deformed element surface is a parameter of a damage process in a structural material. Its density depends on amplitude and duration of mechanical loading. The parameter of sample structural material accumulated damage under mechanical loading characterizes exhaustion of the plasticity resource, both at periodic and monotonic deformation, Pysarenko et al. (2019). Plastic deformation develops in a limited number of microvolumes, their number increases with the increase in loading cycles, Alfyorova et al. (2018). It was shown that an increase in the specific density of slip bands develops as a damped process of cyclic hardening of a material, Maslak et al. (2019). Figure 1 illustrates surface topograms images of the surface of an aluminum alloy sample at different stages of alternating loading, Shanthraj et al. (2011).

Fig. 1. Images of the specimen surface of alloy D16T after cyclic loading: (a) 2 · 10 3 cycles; (b) 7 · 10 3 cycles; (c) 5 · 10 4 cycles.

The aim of this work is to develop an approach to apply deformation statistical characteristics of discrete distribution on a metal material surface under fatigue as a part to develop methods for non-contact analysis of durability and residual life in structural elements.

Nomenclature N cycles σ а

stress amplitude

k D accumulated damage I 0 and I i initial and current values of the deformation damage area parameter R 2 reliability of approximation

2. Research results The analysis of changes in the microrelief of a material surface layer was performed using the method described in Ravanellia et al. (2017) and Meireles et al. (2012). The diffuse scattering parameters of the laser beam reflected from the deformed surface correlate with the characteristic of discrete surface deformation distribution, Lacomte et al. (2006).