PSI - Issue 13

Ho-Wan Ryu et al. / Procedia Structural Integrity 13 (2018) 1932–1939 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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different behavior with those under monotonic loading. Plenty of experiments have been done to understand deformation behavior under a low cycle fatigue condition by Kim et al. (2016, 2017). From previous experimental researches, it is found that the effect of strain rate on the fracture resistance is independent and load ratio (R) has significant effect on fracture behavior under cyclic loading conditions. An effort to simulate a deformation behavior of component in numerical analysis was also made by many researchers. To predict a complex material behavior under cyclic loading condition, cyclic hardening rules are suggested for last 5 decades. From isotropic hardening model to complicated combined hardening models by Chaboche et al. (1979), Chaboche (1991) and Ohno and Wang (1993), there are many models were developed for applying to numerical simulation. Isotropic hardening and linear kinematic hardening which is suggested by Prager (1956) are quite simple to application. But, there are some limitations to predict hardening curvature and change of yield surface in cyclic deformations precisely. Representatively, Chaboche developed a combined hardening model which is combined isotropic hardening and nonlinear kinematic hardening suggested by Amstrong (1966). This model can be used to predict deformations more precisely. But, there are some difficulties to determine many parameters for simulations. There are so many researches to predict cyclic deformation behavior in non-defected component with hardening rules. But, works on the problem of defected or cracked components is limited because of severe deformations in a cracked region. Sherry and Wilkes (2005) and Klingbeil et al. (2016) reported the results of ductile fracture simulation with compact tension (C(T)) under cyclic loading conditions. A simple isotropic hardening model was adopted in simulations of Sherry and Wilkes (2005), whereas a kinematic hardening model in the research of Klingbeil et al. (2016). In these results, they showed that fracture behavior can be predicted with the determined damage models. However, the deformation differences occurred from hardening rules are not analyzed. In this paper, the determination procedures of combined hardening parameters were demonstrated based on limited material test data. Furthermore, the effect of each parameter is analyzed using numerical simulations. Hysteresis loops from three different strain amplitudes were used to determine hardening parameters and Test data from two materials (SA312 TP316 SS and CF8A CASS) and two stress ratios (R=-0.5, -1.0) were used to simulate cyclic C(T) simulation. A debonding option was implemented in ABAQUS (2016) for the simulation of crack growth in numerical analysis. Then, the effect of each parameter from the combined hardening rule were obviously compared.

Nomenclature 

displacement increment

R

load ratio

 a

crack extension

 ,  i

back stress

strain amplitude stress amplitude

 a

 a

cumulative plastic strain equivalent plastic strain size of yield surface

 pl,cum

 pl,eq

 o

C(T)

compact tension

SS stainless steel CASS cast austenite stainless steel FE finite element LLD load line displacement RT room temperature LCF low cycle fatigue YS yield strength