Page 8 - dysertaciyahrynenko

8

introduction of optical-digital image correlation (ODIC) in experimental and

finite element method (FEM) in theoretical mechanics of materials, the possibility

of precise research of local strain not only of the surface but also of the internal

volumes of the material appeared. Since experimental studies have shown that the

damage and fracture accumulation of cylindrical steel samples under static tension

begins in the internal volumes of the material, and not from the surface, the actual

task and purpose of this work is to model and determine the stress-strain state

(STS) of the modified Bridgman sample for its elastoplastic strain by axial quasi-

static stretching at different levels of pre-strain and hydrogen-charge. The object

of the study is the local stress-strain state (STS) and material damage in the

vicinity of the stress concentrator under complex loading. The subject of research

is models and methods for evaluating the strength and resistance to fracture of

structural elements at different levels of pre-strain and hydrogen-charge.

The work includes an analytical review of modern theoretical and

experimental approaches to the mechanics of deformable solids, which are used

to establish the strain and fracture patterns of structural materials under complex

loading. The main strength criteria are given and an analysis of the characteristics of

the material's resistance to fracture is made.

Taking into account the analysis carried out, the scientific and technical

task of assessing the strength and resistance to fracture of low-carbon steels,

which are used for the manufacture of structural elements of thermal power

equipment and pipelines, taking into account their possibility to be hydrogen-

charged, is set and solved in the work. The paper proposes a theoretical-

experimental approach to predict the resistance to fracture of structural elements

based on the damage accumulation model using the energy approach. One of the

unique characteristics of the proposed approach is that it uses local parameters of

the STS, which are determined by a highly accurate and easy-to-use non-contact

method of ODIC, which can be used both in laboratory conditions and for

structural elements under real operating conditions. The proposed method of