PSI - Issue 39

Ilia Nikitin et al. / Procedia Structural Integrity 39 (2022) 599–607 Author name / StructuralIntegrity Procedia 00 (2019) 000–000

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When the crack is developed the regions of spherical particles can be observed only is localized zones. These zones are forming due to very complex shape of the crack path under torsion loading that provide a local contact of crack lips even at the later stages of crack growth.

Fig. 6. The initial stage of torsion crack growth in the plane of maximum shear stress (left) and neighboring region covered by spherical particles (right). 4. Discussions The results of numerical simulation on spatial damage developing in the smooth specimen under fully reversed (R=-1) torsion loading is presented on fig.7. Parameters of model are equal to  =0.5, 1     ,  =0.5, *  =0.98.

Fig. 7. Results of torsion crack path numerical simulation with outlined mechanisms of crack opening.

The model allows to identify the elements and corresponding dominated mechanisms in each cell. It was obtained that at the initial stage of damage developing the dominating mechanism was Mode II crack opening. The damage function reaches the critical values by the CSV criterion. At the later stages the normal crack opening mechanism is turned to be a dominated. The damage zone developing turned to the plane of maximum normal stress. The same scenario of fatigue crack growth was observed in the VHCF tests on titanium alloy.