The paper presents a simple but efficient new numerical scheme for the integration of nonlinear constitutive equations. Although it can be used for the integration of a system of algebraic and differential equations in general, the scheme is primarily developed for use with the direct solution methods for solving boundary value problems, e.g. explicit dynamic analysis in ABAQUS/Explicit. In the developed explicit scheme, where no iteration is required, the implementation simplicity of the forward-Euler scheme and the accuracy of the backwardEuler scheme are successfully combined. The properties of the proposed NICE scheme, which was also implemented into ABAQUS/Explicit via User Material Subroutine (VUMAT) interface platform, are compared with the properties of the classical forwardEuler scheme and backwardEuler scheme. For this purpose two highly nonlinear examples, with the von Mises and GTN material model considered, have been studied. The accuracy of the new scheme is demonstrated to be at least of the same level as experienced by the backward-Euler scheme, if we compare them on the condition of the same CPU time consumption. Besides, the simplicity of the NICE scheme, which is due to implementation similarity with the classical forwardEuler scheme, is its great advantage.
COBISS.SI-ID: 11946779
Springback, a phenomenon that is governed by elastic strain recovery after the removal of forming loads, is of great concern in sheet metal forming. There is no doubt that in this regard, physically reliable numerical modelling of the forming process and predictions of springback obtained by respective computer simulations are crucial for controlling this problem. Unfortunately, by currently available approaches, springback still cannot be adequately predicted in general. In this paper, a new constitutive model is proposed which considers simultaneously sheet anisotropy, damage evolution and strain path-dependent stiffness degradation during sheet metal forming. For parameter identification of the built constitutive model, a particular experimental procedure is developed and an optimization procedure is employed to solve the inverse problem that arises. The proposed approach to constitutive modelling is validated in the end by a simulation of the springback in the formed HSS steel sheet. The simulation results, which prove to be in good agreement with the experimental ones, lead to the conclusion that accurate modelling only of anisotropic yielding is not enough to accurately predict the springback phenomenon; the constitutive model should also include the strain path-dependent change of the elastic moduli.
COBISS.SI-ID: 11877915
In the paper by an inverse numerical procedure the temperature dependent thermal and mechanical material parameters are identified from given experimental data for an austenite stainless steel 316L (AISI). The adequacy of the adopted material consitutive model and identified material parameters is shown by simulating numerically three-pass butt welding experiment. Good agreement between the calculated results and data from the literature is found. Moreover, annealing of the welded plate for residual stress-relief was simulated numerically. The obtained reduction of residual stresses is found to be in agreement with the amount of the residual stress reduction provided from literature. Appropriateness of using a viscous power constitutive law and the adequacy of the presented material characterisation procedure in modelling of thermo-mechanical processes is thus demonstrated.
COBISS.SI-ID: 12226587