R. P. Cardoso

Development of a one point quadrature shell element for nonlinear applications with contact and anisotropy

A general purpose shell element for nonlinear applications including sheet metal forming simulation is developed based on reduced integration with one point quadrature. The developed shell element has five degrees of freedom and four nodes. It covers flexible warping behavior without artificial warping correction. A physical stabilization scheme with the assumed natural strain method is employed to derive a strain field that can be decomposed into the sum of a constant and a linear term with respect to the natural coordinates. The rigid body projection is introduced to treat rigid body rotations effectively. The shell element incorporates elasto-plastic planar anisotropic material models based on the incremental deformation theory. Linear and nonlinear patch tests are performed and the results are compared with analytical or previously reported results. Simulations that include impact and deformable body contact are performed to show the robustness of the contact algorithm. Finally, to demonstrate the capability of handling anisotropic materials, the developed shell element is used for the circular cup drawing process simulation in order to predict the earing profile of Al 2008-T4 alloy sheet.

SEMIAUTOMATED ULTRASONOGRAPHIC MEASUREMENT OF FETAL NUCHAL TRANSLUCENCY USING A COMPUTER SOFTWARE TOOL

Nuchal translucency (NT) thickness measurement has been recently proposed as a part of routine ultrasound scanning during the late first trimester of pregnancy, for the early screening of chromosomal abnormalities. Manual determination of NT is currently performed using electronic calipers placed by the operator in the middle of two echogenic lines displayed on the screen. Therefore, intraobserver and interobserver repeatability can be questioned. This paper presents a software tool that has been developed for achieving this goal in a semiautomatic way, improving the reproducibility of the method.

One point quadrature shell elements for sheet metal forming analysis

SummaryNumerical simulation of sheet metal forming processes is overviewed in this work. Accurate and efficient elements, material modelling and contact procedures are three major considerations for a reliable numerical analysis of plastic forming processes. Two new quadrilaterals with reduced integration scheme are introduced for shell analysis in order to improve computational efficiency without sacryfying accuracy: the first one is formulated for plane stress condition and the second designed to include through-thickness effects with the consideration of the normal stress along thickness direction. Barlat’s yield criterion, which was reported to be adequate to model anisotropy of aluminum alloy sheets, is used together with a multi-stage return mapping method to account for plastic anisotropy of the rolled sheet. A brief revision of contact algorithms is included, specially the computational aspects related to their numerical implementation within sheet metal forming context. Various examples are given to demonstrate the accuracy and robustness of the proposed formulations.

Multi-resolution MPS method

Abstract In this work, the Moving Particle Semi-implicit (MPS) method is enhanced for multi-resolution problems with different resolutions at different parts of the domain utilising a particle splitting algorithm for the finer resolution and a particle merging algorithm for the coarser resolution. The Least Square MPS (LSMPS) method is used for higher stability and accuracy. Novel boundary conditions are developed for the treatment of wall and pressure boundaries for the Multi-Resolution LSMPS method. A wall is represented by polygons for effective simulations of fluid flows with complex wall geometries and the pressure boundary condition allows arbitrary inflow and outflow, making the method easier to be used in flow simulations of channel flows. By conducting simulations of channel flows and free surface flows, the accuracy of the proposed method was verified.

Subspace analysis to alleviate the volumetric locking in the 3D solid-shell EFG method

The main objective of this work is to reduce the volumetric locking pathology at the Element Free Galerkin (EFG) 3D solid-shell meshless method. For this purpose, a subspace analysis is performed in order to extract the linearly independent incompressible deformation modes that can be reproduced by different background integration cells. Additional deformation modes reproduced by a cell configuration produces more flexibility for the meshless formulation. The Enhanced Assumed Strain (EAS) method is blended with the EFG formulation in such a way that additional (mathematical) variables are included in the formulation increasing its flexibility for nearly incompressible materials. Three numerical examples show the effect of the EAS formulation in alleviating the locking pathology for an almost incompressible material condition.

Benchmark 2 – Springback of a Jaguar Land Rover Aluminium

The aim of this benchmark is the numerical prediction of the springback of an aluminium panel used in the production of a Jaguar car. The numerical simulation of springback has been very important for the reduction of die try outs through the design of the tools with die compensation, thereby allowing for the production of dimensionally accurate complex parts at a reduced cost. The forming stage of this benchmark includes one single forming operation followed by a trimming operation. Cross-sectional profiles should be reported at specific (provided) sections in the part before and after springback. Problem description, tool geometries, material properties, and the required simulation reports are summarized in this benchmark briefing.

Development of a One Point Quadrature EAS Solid‐Shell Element

A correct reproduction of thickness effect can be accurately described by the use of three‐dimensional solid elements. In addition to convenient formulation for constitutive law, solid element provides a straightforward extension to geometrically non‐linear problems, particularly in the presence of large rotations, since only translational degrees of freedom are involved. Also, compared with shell elements, it is valid to consider double‐sided contact because of real physical nodes on top and bottom surfaces without any further modification. However, for low order elements, as thickness/length ratio value tends to zero, the transverse shear‐locking phenomenon becomes more evident. Also, plasticity leads to isochoric deformation, which is the main source of the volumetric locking phenomenon. Concerning bending dominant problems, it is difficult to use a single layer of solid elements due to the limitation of integration points along thickness direction. Multi‐layered solid element increases the CPU time dr...

A quadrilateral mesh generator for adaptive procedures in bulk forming processes

The simulation of real industry metal forming processes often requires the presence of adaptive procedures. With that purpose a quadrilateral mesh generator was developed. The algorithm is based on the simple fact that it is always possible to subdivide a region into quadrilaterals whenever the polygonal line that forms its boundary has an even number of sides and that, by joining two contiguous triangles, a quadrilateral may be formed. Rather than using an advancing front technique a cloud of nodal points is initially formed based on error estimators and criteria to define an optimal element size. With this procedure, using an adaptive process, the refinement is created where it will be needed.

Benchmark 4 - Wrinkling during cup drawing

Benchmark-4 is designed to predict wrinkling during cup drawing. Two different punch geometries have been selected in order to investigate the changes of wrinkling amplitude and wave. To study the effect of material on wrinkling, two distinct materials including AA 5042 and AKDQ steel are also considered in the benchmark. Problem description, material properties, and simulation reports with experimental data are summarized.At the request of the author, and Proceedings Editor, a corrected and updated version of this paper was published on January 2, 2014. The Corrigendum attached to the updated article PDF contains a list of the changes made to the original published version.

A general purpose one point quadrature shell element based on resultant-stress

Robustness, accuracy and good computational performance for large scale models are some of the salient requirements for general purpose finite element programs. A new one point quadrature shell element based on resultant‐stress that meets all these requirements has been developed and implemented in MSC.Marc. The finite element strain‐displacement matrices are described in convective coordinate system for the efficient implementation of physical stabilization procedure and Assumed Natural Strain (ANS) methods. For improved warping behavior, an element based fiber coordinate system is constructed at each node. In order to increase the computational efficiency of the shell element, the resultant‐stress equations are formulated by reducing dimensionality into the shell’s mid‐surface. Rigid body projection is performed to prevent artificial strains induced by rigid body rotations. Several examples are presented to demonstrate the element’s efficiency and robustness.