PSI - Issue 57

Giovanni M. Teixeira et al. / Procedia Structural Integrity 57 (2024) 670–691 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 2. Example of cyclic stress strain curve predicted by Frederic- Armstrong’s model. Young’s modulus E= 120000, yielding limit Sy=120, kinematic hardening coefficient H=60000, saturation parameter b=1700.

Where  controls the stabilization rate and R ∞ defines the maximum size of the yield surface. Assuming the drag stress R is zero in the absence of plastic strains, the integration of equation 6 yields: = ∞ (1 − (− , )) (7) Figure 3 shows how the yield stress moves from its original value of 150MPa towards the saturation value 250MPa as the accumulated plastic strain increases.

Fig. 3. The effect of the drag stress R on the yield surface.

Isotropic softening is predicted when R ∞ is negative whereas isotropic hardening is predicted if R ∞ is positive, as illustrated in figure 4. The figure doesn’t show the stabilized loop but rather just the evolution of the yield surfaces towards the saturation value of 250MPa.