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. 4. Frederick- Armstrong and Voce’s combined hardening model. E= 120000, Sy=150, H=60000, b=1700, R ∞ =100,  =30.

The yield criterion for the nonlinear combined model can therefore be defined as: = | − | − − 0 where 0 , and are the yield stress, drag stress and backstress respectively. 1.2. The Unified Viscoplastic Chaboche Model Chaboche [9] proposed the backstress was represented by a combination of Frederick-Armstrong terms: = ∑ 1 (9) where N is the number of F-A terms employed. The evolution of these terms is evaluated by a differential equation of the form: = 2 3 − | | (10) where H i and b i are parameters to be calibrated against experimental data. According to Chaboche three terms are usually sufficient in most simulation cases. The addition of multiple terms allows for a better description of the material response across a wide range of strains. The viscoplastic behavior is described by the equation: ̇ = ⟨ | − |− − 0 ⟩ (11) Where Z and n are the viscosity parameters. In this context creep is added to the model in accordance with Norton’s creep law [7] as follows: = ̇ 1 (12) (8)