PSI - Issue 42
D. Kosov et al. / Procedia Structural Integrity 42 (2022) 545–552 Author name / Structural Integrity Procedia 00 (2019) 000 – 000
551
7
A qualitative analysis of the distribution of the damage parameter over the wall thickness in the zone of the notch root is shown in Fig 5b. From the plot it can be seen that under a combination of tension, internal pressure and torsion, the accumulated damage is distributed through the entire thickness of the wall, and the maximum value of the damage parameter is observed at the top of the notch root. However, in the interaction of compression, internal pressure and torsion, damage accumulation does not start from the inner wall, but from the middle of the wall thickness. The same effect is observed in the interaction of compression and internal pressure. The traditional way to assess the effect of a complex stress state on material properties is to compare experimental data with classical strength theories. For this purpose, the theory of maximum normal stresses, the theory of maximum shear stresses, the generalized Pisarenko-Lebedev criterion in the form (6) are used:
(1 ) eqv
+ −
(6)
1
tension
where the constant is determined by the ratio of tensile strength to compressive strength. For the considered aluminum alloy this material constant is χ=0.97 .
Fig. 6. Ultimate state diagram
(1 - theory of maximum normal stresses; 2 – theory maximum shear stresses; 3 - equivalent to von Mises, taking into account damage; 4 - Pisarenko-Lebedev criterion)
Fig. 6 shows a comparison of classical strength theories and numerically obtained values of ultimate stresses for six variants of a complex stress state of aluminum alloy 2024 in coordinates normalized to the yield strength. It follows from the diagram that in the first quadrant of the limit state diagram at the biaxiality ratio, the theory of maximum normal stresses better describes the limit state. However, in the fourth quadrant, with the negative biaxiality ratio, it is necessary to use the Pisarenko-Lebedev criterion. Conclusions The object of the study was smooth specimen and hollow specimen with a notch. The values of limit stresses were experimentally determined by testing hollow cylindrical specimens under tension, torsion, internal pressure, and their combinations.
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