PSI - Issue 65

A.N. Romanov / Procedia Structural Integrity 65 (2024) 200–208 A.N. Romanov / Structural Integrity Procedia 00 (2024) 000–000

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3. Results and their discussion.

Steel 22k because of deformation aging and a related decrease in plasticity compared with plasticity at room temperature from cyclically stable became a cyclically hardening material (Fig.2,a). As shown in Fig. 2,a, in the first half-cycle of loading, the material hardens significantly (loop width decreases). Then, a transient period of stable development is observed and starts to harden after the transient period (about 100 loading cycles). There was no unilateral strain accumulation (Fig.2,b). After the transition period, the width of the hysteresis loop (hardening) and the accumulation of insignificant strain begin to decrease. And only at durability less than 100 cycles did quasi-static failure occur. In this case, the limiting factor is the loss of plastic deformation stability in the last half-cycle. Failure occurs with the formation and growth of a crack up to the limit value, followed by brittle failure. a b

Fig.2. Variation curves of the cyclically reversible (a) and unilaterally accumulated (b) deformations of steel 22k.

The kinetics of damage accumulation from cyclic (Fig.3,a) and accumulated (Fig.3,b) strains occur in accordance with changes in deformation characteristics. a b

η

Fig.3. Half-cycle tensile strain damage (a) and accumulated strain damage (b) of 22k steel at 270 0 C.

Accumulation proceeds mainly due to cyclic reversible deformation (Fig.3,a). Moreover, the contribution to the total damage from reversible deformation (deformation in the tensile half-cycle) increases with increasing durability at Np = 86 cyc[es η = 0.45 and at Np = 2010 cycles it amounted to η = 0.6. As shown in Fig.4,a, strain aging by strengthening the material restrained the accumulation of strain and kept the true stresses constant at all stages of deformation. The elastic strain damage calculated from Equation (6) (Fig.4,b) does not exceed 20%. The kinetics and extent of plastic deformation (reversible and accumulated) determine the contribution of each component to the total, including ultimate and permanent damage accumulation (Fig.5).