Explicit Analysis of Sheet Metal Forming Processes Using Solid-Shell Elements

To simulate sheet metal forming processes precisely, an in-house dynamic explicit code was developed to apply a new solid-shell element to sheet metal forming analyses, with a corotational coordinate system utilized to simplify the nonlinearity and to integrate the element with anisotropic constitutive laws. The enhancing parameter of the solid-shell element, implemented to circumvent the volumetric and thickness locking phenomena, was condensed into an explicit form. To avoid the rank deficiency, a modified physical stabilization involving the B-bar method and reconstruction of transverse shear components was adopted. For computational efficiency of the solid-shell element in numerical applications, an adaptive mesh subdivision scheme was developed, with element geometry and contact condition taken as subdivision criteria. To accurately capture the anisotropic behavior of sheet metals, material models with three different anisotropic yield functions were incorporated. Several numerical examples were carried out to validate the accuracy of the proposed element and the efficiency of the adaptive mesh subdivision.

Aerodynamic Pressure Mapping Technique from CFD to FEM Model of N219 Winglet

Due to relatively complex geometry of N219 winglets, CFD simulations have to be conducted to predict the aerodynamic load by the structure in some critical flight conditions. Since the aerodynamic CFD model is not the same as the finite element model of the structure, there is a need to accurately transform the load data between the two models. This paper discusses a simple alternative technique to map pressure distribution from the mesh or face zone of a CFD simulation to an FEM model using a Matlab based in-house code program. The technique focuses on how an FEM shell element has same pressure value with its nearest CFD element. Although the cumulative forces sometimes give different result, the pressure distribution is highly accurate, moreover when the FEM model has smoother elements. Validation has been conducted by comparing with other pressure mapping technique of a commercial software Patran. The results show a good agreement where the present technique provide a more accurate result especially for the critical biggest load among the cumulative forces in the three-dimensional direction. The proposed technique is currently suitable to evaluate loading characteristics of semi monocoque structures. A further treatment of the technique for other types of structure is currently under development.

An Efficient Computational Model for Magnetic Pulse Forming of Thin Structures

Electromagnetic forming (EMF) is one of the most popular high-speed forming processes for sheet metals. However, modeling this process in 3D often requires huge computational time since it deals with a strongly coupled multi-physics problem. The numerical tools that are capable of modeling this process rely either on shell elements-based approaches or on full 3D elements-based approaches. The former leads to reduced computational time at the expense of the accuracy, while the latter favors accuracy over computation time. Herein, a novel approach was developed to reduce CPU time while maintaining reasonable accuracy through building upon a 3D finite element analysis toolbox which was developed in CEMEF. This toolbox was used to solve magnetic pulse forming (MPF) of thin sheets. The problem was simulated under different conditions and the results were analyzed in-depth. Innovative techniques, such as developing a termination criterion and using adaptive re-meshing, were devised to overcome the encountered problems. Moreover, a solid shell element was implemented and tested for thin structure problems and its applicability was verified. The results of this element type were comparable to the results of the standard tetrahedral MINI element but with reduced simulation time.

Analytical Solution of Composite Curved I-Beam considering Tangential Slip under Uniform Distributed Load

An analytical solution of composite curved I-beam considering the partial interaction in tangential direction under uniform distributed load is obtained. Based on the Vlasov curved beam theory, the global balance condition of the problem has been obtained by means of the principle of virtual work; integrating this by parts, the governing system of differential equations and corresponding boundary conditions have been determined. Analytical expressions for the composite beam considering the partial interaction have been developed. In order to verify the validity and the accuracy of this study, the analytical solutions are presented and compared with other three FEM results using the space beam element and the shell element. The deflection and the tangential slip of the composite curved I-beam are investigated.