P. D. Barros

Earing Prediction in Drawing and Ironing Processes Using an Advanced Yield Criterion

This work aims to contribute to the understanding of the role/influence of advanced yield criteria on the earing profile prediction after drawing and ironing, for a cylindrical cup benchmark proposed at the NUMISHEET 2011 conference [1]. Two typical materials used for can-making were considered and studied: an AA5042 aluminum alloy and an AKDQ steel. The drawing and ironing operations are performed on a special die which allows drawing and ironing in one single punch stroke in order to simplify the real process. The benchmark results report include, for each material: (i) the earing profile after drawing and ironing, presenting the cup height evolution with the angle from the rolling direction, and (ii) the evolution of punch force with punch stroke. This work presents a comparison between experimental and numerical results obtained for the aforesaid benchmark with DD3IMP in-house solver, using two sets of parameters for the Cazacu and Barlat 2001 [2] yield criterion, identified based on uniaxial tensile, equi-biaxial tension and disc compression test results. The first set uses the initial yield stress values while the second one used the flow stress values for an accumulated plastic work of 20 MPa. The results highlight the different impact of the experimental data in the earing prediction for both materials: the results for the second set are slightly improved for the AKDQ steel while for AA5042 the effect is negligible. The improved earing prediction obtained with the second set for the AKDQ steel seems to result from a better description of the stress states that occur in the flange zone.

DD3MAT - a code for yield criteria anisotropy parameters identification.

The authors gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) via the projects PTDC/EME-TME/118420/2010 and UID/EMS/00285/2013. The first author is also grateful to the FCT for the PhD grant SFRH/BD/98545/2013.

Trimming of 3D solid finite element meshes: sheet metal forming tests and applications

Abstract Over the last years, the numerical simulation of integrated processes has become the major challenge in virtual try-out of sheet metal components, including trimming operations that may occur between forming steps. Detailed simulation of trimming processes is a challenging task, particularly when integrated with other forming operations such as deep drawing or hemming. A simplified approach can be adopted in which elements outside the trim surface are deleted from the finite element (FE) model adjusting the remaining to the surface. Following this approach, the state variables are mapped from the old FE mesh to the new trimmed mesh to continue the simulation. This paper addresses this simplified approach to the trimming process exploring a previously presented algorithm (Finite Elem Anal Des 42: 1053–1060, Baptista et al. 2006), which allows the treatment of hexahedral finite element meshes. Particularly, it focuses on the performance evaluation of the implemented strategies for correcting the FE mesh to the trimming surface, including the treatment of pentahedral-shaped elements. Different correction and treatment strategies are evaluated on different types of meshes, based on numerical simulation results of simple mechanical tests: uniaxial tensile test and simple bending test. Finally, two practical applications are given where the local effect of the trimming algorithm is highlighted.

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...

Pre-strain effect on springback of 2D draw bending

This work focuses on the BENCHMARK 4 – pre-strain effect on springback of 2-D draw bending, proposed under the NUMISHEET 2011 conference (Huh et al., 2011), where the deep drawing of a U-rail is performed considering the same base material, submitted or not to an 8% tensile pre-strain. A DP780 steel with a thickness of 1.4 mm is studied. The analysis considers all the results reported in Huh et al. (2011) and the ones obtained using DD3IMP. Experimental and numerical results show that the pre-strain leads to a springback increase, showing the influence of the yield stress to elastic modulus ratio. Indeed, the elastic modulus during unloading seems to be as important as the adopted hardening model, being the contribution of the yield criterion smaller. The results accuracy seems to depend more on the strategy adopted to determine the material constitutive parameters than on the selected constitutive model.