Explicit Dynamic Finite Element Model Research Articles

Rotary forging with double symmetry rolls

A novel metal plastic forming technology, namely rotary forging with double symmetry rolls (DSRs) is presented in comparison to more conventional single roll rotary forging. Based on a reliable three-dimensional elastic–plastic dynamic explicit finite element model, the fundamental deformation characteristics of cold rotary forging with DSRs of a cylindrical workpiece are made clear. Meanwhile, the interactive effects of two main processing parameters, feedrate v of the lower die and rotational speed n of the two upper dies on the forming process have been comprehensively revealed. As a specific case, hot rotary forging of a spiral bevel gear was analysed and an experiment was carried out on a developed hot rotary forging press with DSRs. The simulation results are in good agreement with the experimental ones and demonstrate that rotary forging with DSRs has a potential prospect in forming a complex spiral bevel gear. The results of this research help to better understand the advanced metal plastic forming technology of rotary forging with DSRs.

Deformation characteristics and mechanisms of the cold rotary forging of a ring workpiece

Cold rotary forging is an advanced but very complex incremental metal plastic-forming technology under coupled effects with multifactors. Previous research concentrates mainly on the study of the cold rotary forging process of a cylindrical workpiece and thus it is essential to explore the deformation characteristics and mechanisms of the cold rotary forging of a ring workpiece in order to use rotary forging presses with maximum efficiency. In the current paper, numerous simulations have been carried out based on a valid three-dimensional elastic-plastic dynamic explicit finite element model developed using ABAQUS software. Through these simulations, the interactive effects of three main processing parameters, the feed rate v of the lower die, rotational speed n, and inclination angle γ of the upper die on the cold rotary forging process of a ring workpiece, have been thoroughly explored. Furthermore, a comprehensive and decisive factor in cold rotary forging, namely the equivalent feed amount per revolution Q, is put forward, and its effects on the forming process have also been thoroughly revealed. The results obtained are explained with regard to the plastic penetrating states of the deformed ring workpiece. The results of this research thoroughly reveal the deformation characteristics and mechanisms of cold rotary forging of a ring workpiece, and provide valuable guidelines for optimizing the processing parameters so as to control precisely the cold rotary forging process of a ring workpiece.

Effect of anisotropy, kinematic hardening, and strain-rate sensitivity on the predicted axial crush response of hydroformed aluminium alloy tubes

There exists considerable motivation to reduce vehicle weight through the adoption of lightweight materials while maintaining energy absorption and component integrity under crash conditions. Aluminium and magnesium alloys, advanced high-strength steels, and composites are all proposed candidates for replacing mild steel in automotive structures. It was of particular interest to study the crash behaviour of lightweight tubular hydroformed structures. Thus, the current research has studied the dynamic crush response of hydroformed Al–Mg–Mn aluminium alloy tubes using both experimental and numerical methods. The research focused on axial crush structures that are designed to absorb crash energy by progressive axial folding. The main experimental parameter that was varied during the hydroforming process was the corner-fill radius of the tube. Numerical studies were carried out using explicit dynamic finite element models incorporating advanced constitutive material models to capture the measured forming and crash history. A constitutive model was implemented in the finite element models combining the Johnson–Cook strain-rate sensitivity model, a non-linear isotropic-kinematic hardening model, and the Yld2000-2d anisotropic model. Each effect was isolated, and it was shown that strain-rate sensitivity slightly increased the energy absorption capabilities while kinematic hardening and anisotropy effects decreased the energy absorption capabilities during axial crush. When including all three effects, the predicted energy absorption was less than the response predicted from simulations performed using the von Mises yield criterion and in reasonable agreement with measured data. It is recommended that a combined constitutive model be utilized for the study of materials that show sensitivity to the Bauschinger effect, strain-rate effects, and anisotropy.

Finite element simulation of sheet metal stamping with polycrystalline plasticity

The rate-dependent crystalline plasticity constitutive model is introduced into Mindlin shell element and dynamic explicit finite element method. A tangent modulus method is employed to calculate plastic strain increment. The crystal orientations are as- signed to finite element integration points and the stress of polycrystalline is calculated according to the normal distribution charac- teristic of orientation distribution function (ODF) in orientation space. 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. The stamping process of a rolled aluminum sheet, whose initial main textures are Cu and S texture for a square punch is numerically studied. The validity of proposed model is proved through the comparison between numerical results and experimental ones. By the crystalline plasticity finite element method, not only the sheet metal deformation process during stamping can be simulated, but also the evolu- tion of sheet metal texture can be predicted. During the box stamping process, Cu and S textures are not stable and transform to other orientations gradually.

Utilizing the Explicit Finite Element Method for Studying Granular Flows

Granular flows are systems of complex dry particulates whose behavior is difficult to predict during sliding contact. Existing computational tools used to simulate granular flows are particle dynamics, cellular automata (CA), and continuum modeling. In the present investigation, another numerical tool—the explicit finite element method (FEM)—is analyzed as a potential technique for simulating granular flow. For this purpose, explicit dynamic finite element models of parallel shear cells were developed. These models contained 52 particles and consisted of granules that are both round and multi-shaped (diamond, triangle, and rectangle). Each parallel shear cell consisted of a smooth stationary top wall and a rough bottom surface that was given a prescribed velocity of U = 0.7 in/sec (1.78 cm/s). The coefficient of friction (COF) between the particle–particle and particle–wall collisions was varied between 0.0 and 0.75. Utilizing the output of the simulations, results are presented for the shear behavior, particle kinetic energy, and particle stresses within the shear cell as a function of time. As a means of validating the explicit technique for granular flow, a 75 particle, zero roughness, couette shear cell model (solid fraction of 0.50) is subsequently presented for which direct comparisons are made to the results published by Lun. [Lun, C.K. et al.: Phys. Fluids 8, 2868–2883 (1996)] Overall, the results indicate that the explicit FEM is a powerful tool for simulating granular flow phenomena in sliding contacts. In fact, the explicit method demonstrated several advantages over existing numerical techniques while providing equivalent accuracy to the molecular dynamics (MD) approach. These advantages included being able to monitor the collision (sub-surface and surface) stresses and kinetic energies of individual particles over time, the ability to analyze any particle shape, and the ability to capture force chains during granular flow.

Dynamic behavior of a homogenized composite under contact with friction loading

This work is devoted to the numerical study of a composite under dynamic contact with friction loading, known as tribological loading. A dynamic explicit finite element model is used and Lagrange multipliers allow determining the local forces due to contact and friction. The convergence of numerical contact with friction models, achieved by using a regularized Coulomb friction law, is presented first. This study also shows the equivalence between the results obtained with heterogeneous and homogeneous materials under dynamical tribological loading. The homogeneous models are built by calling on classical homogenization theory because the main wavelength of the loading is much higher than that of the heterogeneities and the contrast between elastic properties is low. To cite this article: G. Peillex et al., C. R. Mecanique 335 (2007).

The establishment of a failure criterion in cross wedge rolling

Internal defects in the cross wedge rolling (CWR) process can lead to the catastrophic failure of products. Using specialised experiments and the explicit dynamic finite element model (FEM), this work investigates the mechanisms of void generation and growth in the cross wedge rolling process. Based on a combined numerical and experimental approach, the morphology of void generation is determined as a function of the workpiece material and three primary parameters in the cross wedge rolling process: the forming angle, α, the stretching angle, β and the area reduction, ΔA. Through the definition of a non-dimensional deformation coefficient, e, a method for predicting the likelihood of void formation is subsequently ascertained and discussed with respect to CWR tooling design and operating conditions.