Dayong Li

A Crystalline Plasticity Finite Element Method for Simulation of the Plastic Deformation of AZ31 Magnesium Alloys

In this paper, a constitutive framework based on a crystalline plasticity model is employed to simulate the plastic deformation of AZ31 magnesium alloy, which posses the hexagonal close packed (HCP) crystal structure. Dislocation slip and mechanical twinning are taken into account in the model. The successive integration method is used to determine the active slip systems, and the contribution of twinning to the grain reorientation is treated by the PTR method. The FE model is introduced into ABAQUS/Explicit through a user material subroutine (VUMAT). Three deformation processes of AZ31 magnesium alloy, including tension, compression and a stamping process, are simulated with the present method. The simulation results are compared with experiment and those presented in the literature.

Crystal plasticity finite element modelling of the extrusion texture of a magnesium alloy

In this paper, a crystal plasticity finite-element model (CPFEM) is developed to simulate the hot extrusion texture of the magnesium alloy AZ31. The crystal plasticity model is implemented in ABAQUS™ via user interface VUMAT subroutine. The elasto-plastic self-consistent (EPSC) model is used as the basic polycrystal framework to simulate the slip and twinning during the extrusion. Furthermore, this framework is extended to account for the effects of the dynamically recrystallized (DRX) grains on the extrusion textures. Good agreement is found between the experimentally measured and simulated textures. The simulation results show that the presence of a secondary texture component around || extrusion direction (ED) can be attributed to the lattice rotation around the c-axis during the formation of the DRX grains. In addition, the shear strain imposed on the extruded material affects the resulting texture by enhancing the basal slip mode as the material passes through the extrusion opening.

Effect of Rate Sensitivity on Necking Behavior of a Laminated Tube Under Dynamic Loading

An elastic-viscoplastic based finite element model has been developed to study the necking behavior of tube expansion for rate independent materials, rate dependent monolithic materials, and laminated materials during dynamic loading. A numerical study shows that for rate independent materials, the dynamic loading will not delay diffused necking but localized necking; for rate dependent materials, high strain rate sensitivity can significantly delay the onset of localized necking for both monolithic and laminated sheets and affect the multiple-neck formation in high-speed dynamic loading. The model also shows that a higher volume fraction of a clad layer with positive rate sensitivity material in a laminated sheet improves the sheet ductility.

Numerical Simulation of the Roll Forming Process of Aluminum Folded Micro-channel Tube

Micro-channel tube is the most important component of flat tube heat exchangers. The folded microchannel tube is made of clad aluminum sheet through roll forming process, and has great advantage in the aspect of corrosion resistance over extruded tube. The folded tubes sub-millimeter channel size as well as tight dimensional precision requirement brings great challenge to roll forming process design. In this paper, the finite element model of the whole roll forming process of a ten-channel tube is established by using ABAQUS/Explicit. The deformation at different forming stands are investigated and compared with experiment. The hydraulic pressure test is carried out on the developed tube and its pressure bearing capacity is evaluated.

A RESHAPING ROLL FORMING TECHNIQUE FOR SQUARE/RECTANGULAR STEEL TUBE MANUFACTURING: NUMERICAL STUDY AND PROCESS DESIGN

Square/rectangular steel tubes are widely used in various industry fields and their quality is related greatly to manufacturing technologies. In this study, a new roll forming technique to manufacture square/rectangular tubes from round pipes is modeled and studied with the finite element method. In the proposed forming process, the horizontal and vertical rolls are installed alternately at the forming stands along the longitudinal direction and the corresponding pass profiles are no longer closed as in conventional reshaping process. The interference between driving horizontal and vertical rolls can be prevented, and more rolls can be used as driving rolls to provide larger driving force. Furthermore, the forming rolls become reusable and can be commonly used in manufacturing the tubes with different sizes. The forming characteristics of the new reshaping process are analyzed and process is designed through comparison among different forming schemes.

Analysis of BCC Sheet Metal Forming by Polycrystalline Plasticity method

The macroscopic deformation behavior of sheet metals is related physically to the microscopic deformation mechanism. For BCC metal, there have three kinds of slip systems, and the rules of the active slip system still not clear. A program is developed based on the proposed crystalline plasticity dynamic explicit finite element model to simulate sheet metal stamping as well as predict texture evolution. A stable proportion factor has been given to the different slip system and introduced into the rate‐independent polycrystalline model. A proper factor has been found by the contrast between the simulation result and experiment data.

Numerical Simulation on Sheet Metal Forming with Rate‐independent Polycrystalline Plasticity FEM

It has long been found that, during deformation process, the crystal orientations would gradually rotate around some ideal orientations, and then would affect the later deformation properties of sheet metal. So it is very important to introduce texture model into metal forming processes. In this paper, a rate‐independent polycrystalline plasticity model is developed and introduced into dynamic explicit element method. Metal flow is assumed to occur by crystallographic slip on given slip systems within each crystal. Every integration point represents a single crystal. Then cup drawing of sheet metal is studied using crystalline plasticity finite element analysis. For the rolled aluminum sheet, which contains strong {001}〈110〉 texture, earing is formed at 45° direction after cup drawing. For the annealing aluminum sheet, due to the balance between two main textures, the flange earing tendency is not obvious. And for the soft steel sheet with a faintish orientation distribution, the flange earing tendency is...