Issue 63

H. A. R. Cruz et alii, Frattura ed Integrità Strutturale, 63 (2023) 271-288; DOI: 10.3221/IGF-ESIS.63.21

As the results of the other models are evaluated, in ascending order of slenderness ratio, there is a gradual reduction in the ultimate resistance load of the prototypes. A common factor in this set of simulations is the failure mode of the specimens, in which global buckling prevailed over local instabilities. Figs. 14 through 15 illustrate the collapse of one of the numerically tested models, with slenderness ratio equal to 200, in the analysis increment referring to its ultimate resistance load and, thus, to the beginning of its global instability. Fig. 16 shows the local failure due to the flattening of the bar, for small indices of slenderness ( 20 ≤ λ ≤ 100). To provide greater clarity to the visualization of the specimen deformation at this loading stage, a scaling factor of 5e+01 was applied to the displacements of the finite element mesh.

Figure 14: Displacements referring to the global buckling of a numerical model example in Abaqus® software, in millimeters (mm).

Figure 15: Von Mises stresses referring to the global buckling of a numerical model example in Abaqus® software, in MegaPascal (MPa).

The displacement and stress results of specimens with slenderness ratios contained in the range of 120 to 200 indicate a brief transition between failure modes due to excessive local deformation of the flattened ends and global buckling of the prototypes. In such a transition, a partial plasticizing is observed in the transition zones of cross-sections of the model with a slenderness ratio equal to 120, although global instability is its characteristic collapse mode. In the following numerical analyses, related to the three models of slenderness immediately greater, a reduction in the level and a change in the location of the highest tensions can be observed. In this set of analyses, the critical stresses of the prototypes moved from the flattened ends of the bars to their central regions. To conclude the series of simulations, the structural behavior of the model with a slenderness ratio equal to 200 under compressive load was defined by the global buckling of the prototype still in the linear elastic regime. This fact is attested by the von Mises stress level reached at this stage of the analysis, whose values are entirely below the yield strength of AISI 1020 steel.

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