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                  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
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