Evaluation of the performance of a nonlinear hardening model under cyclic and proportional loadings

In the present dissertation, a combined hardening model was employed in order to predict the material behavior of a plate with a hole under cyclic loadings. Von Mises yield criterion in conjunction with associated flow rule was utilized in the numerical approach. The kinematic part of the combined hardening rule was model using Armstrong – Frederic model. To incorporate the plasticity models into the finite element software, a user defined material subroutine so-called Hypela2 was used. In the first stage, single element test simulations were carried out to validate to plasticity moıdel used in this work. To this end, cyclic tension – compression and simple reversal shear applications were considered. Kinematic and isotropic hardening parameters were obtained from the monotonic and reversal stress – strain responses of the materials. Numerical results obtained from the finite element analyses were compared with the experimental outcomes and numerical predictions from literature studies. In the second stage, plasticity model with combined hardening model was used so as to determine the material response of a plate with a hole under combined loadings. Within this concept, OHFC copper was considered as a test material. Finite element results were compared with the numerical predictions procured from literature studies. According to the findings obtained in this research, it was concluded that the plasticity model used in this work provide accurate results especially for small strain.cyclic loading. Moreover, this model is user friendly and has an easy identification procedure. Keywords: Combined hardening, plasticity model, cyclic stress – strain behavior, Bauschinger effect, finite element method