D. M. Neto

Numerical modeling of friction stir welding process: a literature review

This survey presents a literature review on friction stir welding (FSW) modeling with a special focus on the heat generation due to the contact conditions between the FSW tool and the workpiece. The physical process is described and the main process parameters that are relevant to its modeling are highlighted. The contact conditions (sliding/sticking) are presented as well as an analytical model that allows estimating the associated heat generation. The modeling of the FSW process requires the knowledge of the heat loss mechanisms, which are discussed mainly considering the more commonly adopted formulations. Different approaches that have been used to investigate the material flow are presented and their advantages/drawbacks are discussed. A reliable FSW process modeling depends on the fine tuning of some process and material parameters. Usually, these parameters are achieved with base on experimental data. The numerical modeling of the FSW process can help to achieve such parameters with less effort and with economic advantages.

Improving Computational Performance through HPC Techniques: case study using DD3IMP in‐house code

The computational efficiency of the FEA is strongly dependent on the algorithmic and numerical efficiency of the FE solver. This is particularly important in case of implicit FE codes, such as DD3IMP, the in‐house static implicit FE solver under analysis in this work. This study describes the procedure adopted to identify the main computational bottlenecks of the FE solver in order to introduce the OpenMP directives and, consequently, to achieve a major speedup of the whole algorithm. The different parallelized branches of the code are tested using the well‐known square cup deep drawing example, considering different FE discretizations. The analysis of the preliminary results, concerning the CPU wall time, allows to demonstrate that the adoption of HPC techniques, such as the abovementioned OpenMP directives, enables to: (i) achieve a speedup factor close to the number of cores (in a single computer); (ii) solve a problem in a shorter time; (iii) solve a bigger problem in the same amount of time and, thus...

Improving Nagata patch interpolation applied for tool surface description in sheet metal forming simulation

The contact surface description is a very important field in the numerical simulation of problems involving frictional contact, which are among the most difficult ones in continuum mechanics, as is the case of sheet metal forming simulation. In this paper, a methodology to control the Nagata patch interpolation of piecewise linear meshes is proposed, in order to improve its applicability for tool surface description used in the numerical simulation of sheet metal forming processes. The interpolation can be applied either to triangular and quadrilateral Nagata patches, as well as structured and unstructured patches. The normal vectors needed for the Nagata interpolation are obtained through two distinct strategies. The first uses the information available in the CAD surface model, while the second resorts only to the piecewise linear mesh model information. In order to evaluate the interpolation accuracy, the Nagata patch is applied to describe a sheet metal forming complex shape part tool geometry. The results obtained show that, regardless of the strategy used to evaluate the surface normal vectors, the use of the proposed Nagata patch interpolation enables a large improvement in the geometric accuracy when compared with the models composed by piecewise linear elements. The use of CAD surface geometry to evaluate the surface normal vectors leads to the best Nagata patch interpolation in terms of shape and normal vector field accuracy.

Local Interpolation for Tools Surface Description

Surface description accuracy is of paramount importance when modeling contact problems. However, most finite element method (FEM) researchers still resort to polyhedral models to describe contact surfaces, which can oversimplify the original system by neglecting the curvature. A simple algorithm for interpolating discretized surfaces and recover the original geometry was recently proposed by Nagata [1]. The main idea behind this parametric surface description (subsequently named Nagata patch) is the quadratic interpolation of a curved segment, from the position and normal vectors at the end points. The curved segment is used to recover the curvature of triangular or quadrilateral patches, defined by the vertices of the polyhedral mesh. This paper presents a study concerning the use of Nagata patches to local interpolate tools surface either defined by analytical functions or polyhedral models. The use of triangular or quadrilateral Nagata patches is compared, both in terms of efficiency and robustness of the local interpolation algorithm. Different strategies to approximate the tools normal defined by polyhedral models are presented and the error in the local interpolation is evaluated.

On the influence of the yield parameters identification procedure in cylindrical cups earing prediction

This work presents a study concerning the deep drawing process of a cylindrical cup, following the process conditions defined on the BENCHMARK 1 - Earing Evolution During Drawing and Ironing Processes, of NUMISHEET 2011 [1]. The deep drawing operation is analyzed for an AA5042 aluminum alloy, which orthotropic behavior is described using the Cazacu and Barlat, 2001 yield criterion [2]. The constitutive parameters were determined based on the experimental data obtained from tensile tests, with different orientations to the rolling direction, disk compression test and the equibiaxial tension test, using DD3MAT in-house code. An analytical approach that relates the earing profile with the ones of both r -values and yield stresses [3,4] is used to understand the influence of the identification procedure on the analytically and numerically predicted earing profile. The numerical simulations of the forming process were performed using DD3IMP in-house code. The analysis shows that, although earing is generally a...

Remapping algorithms: application to trimming operations in sheet metal forming

Most of sheet metal forming processes comprise intermediate trimming operations to remove superfluous material. These operations are required for subsequent forming operations. On the other hand, the springback is strongly influenced by the trimming operations that change the part stiffness and the stress field. From the numerical point of view, this involves the geometrical trimming of the finite element mesh and subsequent remapping of the state variables. This study presents a remapping method based on Dual Kriging interpolation, specifically developed for hexahedral finite elements, which has been implemented in DD3TRIM in-house code. Its performance is compared with the one of the Incremental Volumetric Remapping method, using the split-ring test to highlight their advantages and limitations. The numerical simulation of the forming processes is performed with DD3IMP finite element solver.

Applying Nagata Patches in the Description of Smooth Tool Surfaces Used in Sheet Metal Forming Simulations

This study deals with the new strategy currently implemented in DD3IMP in-house code to describe the forming tools using Nagata patches. The strategy is based on the use of the Nagata patch interpolation to generate smooth contact surfaces over coarse faceted finite element meshes. The description of the adopted algorithm is briefly presented, highlighting the contact search algorithm employed. The reverse deep drawing of cylindrical cups, proposed as benchmark at the Numisheet’99 conference, is selected to examine the accuracy and robustness of the proposed approach. The effect of the gap between the blank-holder and the die is studied, adopting two distinct strategies: fixed gap and variable gap. The numerical results are compared with the experimental ones, previously presented and discussed in [1]. It is shown that the agreement is very good both in terms of punch force evolution and thickness distribution.

A staggered coupling strategy for the finite element analysis of warm deep drawing process

The thermomechanical finite element analysis of warm forming processes enables an improved comprehension of the process parameters affecting the material formability. However, the thermal and mechanical coupling problem is still a challenge from the computational standpoint. A staggered strategy for the thermomechanical coupling problem is presented in this study, which is based on an isothermal split approach and allows the treatment of the two problems separately. The exchange of information between the mechanical and the thermal problem is performed to achieve a compromise between computational cost and accuracy. The proposed algorithm was implemented in DD3IMP in-house finite element code. Its performance is analysed and compared with a classical strategy commonly employed for solving thermomechanical problems.