Constitutive Model For Large Deformation Research Articles

Numerical simulations of regolith sampling processes

We present recent improvements in the simulation of regolith sampling processes in microgravity using the numerical particle method smooth particle hydrodynamics (SPH). We use an elastic-plastic soil constitutive model for large deformation and failure flows for dynamical behaviour of regolith. In the context of projected small body (asteroid or small moons) sample return missions, we investigate the efficiency and feasibility of a particular material sampling method: Brushes sweep material from the asteroid's surface into a collecting tray. We analyze the influence of different material parameters of regolith such as cohesion and angle of internal friction on the sampling rate. Furthermore, we study the sampling process in two environments by varying the surface gravity (Earth's and Phobos’) and we apply different rotation rates for the brushes. We find good agreement of our sampling simulations on Earth with experiments and provide estimations for the influence of the material properties on the collecting rate.

Integration of physically based models into FE analysis: Homogeneity of copper sheets under large plastic deformations

Abstract In this paper, an integration approach consists of implementation of true internal state variables constitutive model to finite element (FE) analysis is presented. From the approach, the deformation homogeneity during severe plastic deformation of sheet (SPD) is investigated. Since there is not any constitutive model for large deformation that based on appropriated physical assumptions, here a new constitutive model is proposed that is entirely based on metallurgical mechanisms. Also, in order to achieve accurate results with low computation time, a new approach for integration of the constitutive model to FE analysis is presented. By coupling the constitutive model and FE analysis, the homogeneity of hardness of severely deformed copper sheet by constrained groove pressing is investigated. A comparison between modeling results and experimental data shows an acceptable agreement. The results show that in contrast to the previous modeling work, increasing the pass number of the process causes to lower inhomogeneity of hardness in processed sheet.

Hot Working — Constitutive Equations and Computational Procedures

A state variable constitutive model for large deformation, isotropic thermo-elasto-viscoplasticity, and an implicit time-integration procedure to integrate the evolution equations for the state variables have been developed. The constitutive equations and time integration procedure have been incorporated into the general purpose finite element computer code ABAQUS via its “user material” subroutine option. By using this program, representative problems have been numerically analyzed. The predictions from the analysis concerning the forging load as a function of ram travel, and the overall shape changes are found to be in excellent agreement with measurements made in similar laboratory experiments.

Some computational aspects of large deformation, rate-dependent plasticity problems

The governing equations for a finite element formulation of boundary value problems for large deformation metal forming processes are derived using a principle of virtual work formulated in a Lagrangian reference system. The updated Lagrangian method is used to simplify the equations. The resulting nonlinear equilibrium equations are solved using Newton's method. A constitutive model for large deformation, rate-dependent plasticity is developed. The model incorporates a one parameter, implicit integration operator for stability and accuracy. The stressrate/strain-rate relation is written in terms of the Jaumann rate of stress. Numerous example problems are solved to demonstrate the effectiveness of the numerical algorithms.