Issue 27

A. Kostina et alii, Frattura ed Integrità Strutturale, 27 (2014) 28-37; DOI: 10.3221/IGF-ESIS.27.04 34 2 : 1 : ( ) p p p T p p T p Q W p                                 where p Q - inelastic contribution to the heat, p W - plastic work. Under isoentropy conditions it has the form: : 1 : ( ) p p p p p Q W p                    Results of modeling Fig. 7 presents the experimental results for tension of Armco iron samples. To simulate the homogeneous part of plastic deformation, we propose the existence of two process steps. The first step is corresponding to the loading of the sample up to yield stress, Luders bunds propagation and unloading. The second step corresponds to the loading of preloaded specimen. During the second step the specimen exhibits the homogeneous plastic deformation, parabolic hardening and decreasing of stored energy ratio. This process can be simulated by definition of nonzero initial deformation. The schematic of the process is presented in Fig. 7. Figure 7 : Experimental stress-strain curve for Armco iron. Numerical simulation of the considered process was carried out in the finite element package Simulia Abaqus 6.13. Fig. 8 shows the finite-element mesh of the specimen. Eight-node linear brick elements were used for the simulation. The above explained model was applied for the material behavior description using the subroutine UMAT. Arrays of material constants, strain, strain increments and the time step passed as input data to the procedure. Increments of the stress tensor components and increments of the defect density tensor components are determined from the system of constitutive equations. Values of these components at the next time step are defined as the sum of the values on the previous step and the appropriate increment. Fig. 9 presents the stress-strain curves obtained from experimental data (dash dot line) and results of numerical simulation (solid line). Results calculated by the model are in a good agreement with experiment. Figure 8 : Finite-element mesh of the specimen.