Finite Element Simulation of Single Point Incremental Sheet Forming With Barlat 2004 Yield Function, CPFEM, and 3D RVE

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URL: http://rave.ohiolink.edu/etdc/view?acc_num=osu1543170842564928

Abstract

In the last two decades, automotive and aerospace industries have been showing increasing interests in understanding and applying a novel flexible manufacturing method known as the Incremental Sheet Forming (ISF) for rapid prototyping and small batch production of sheet metal components. In the first part of this thesis, the results of a detailed literature review is presented to shed light on different aspects of the ISF process including fundamental deformation mechanisms, formability, tool path generation methods, geometric accuracy, compensation techniques, thickness distribution, forming forces and moment, springback, surface finish, as well as efficiency with respect to time and energy. A comprehensive review of the ISF process modeling including analytical, finite element, and damage modeling is also discussed. In addition, a detailed review of other variants of the ISF process including warm incremental sheet forming, electrically-assisted incremental sheet forming, water jet incremental sheet forming, and examples of their applications in various industries, including biomedical applications, is presented.

It is well known that significant out-of-plane shears develop in the sheet metal in the ISF process, which affects material formability and forming limit diagram (FLD). Therefore, it is necessary to use a three-dimensional (3D) yield function to account for normal and shear stress components when modeling the ISF process. To simulate the single point incremental forming (SPIF) of 7075-O aluminum alloy sheet, three different 3D yield functions namely, von Mises, Hill’s 1948, and Barlat Yld2004-18p, were used. The most elaborate of the three yield functions, Yld2004-18p, was implemented into the commercial FEA code ABAQUS as a user material subroutine (VUMAT), by considering the cutting-plane algorithm for the integration of the elasto-plastic constitutive model.

The anisotropy coefficients of Yld2004-18p and Hill's 1948 were calculated using uniaxial tensile test data for AA7075-O. To calibrate the parameters of the non-quadratic anisotropic 3D yield function Yld2004-18p, requires the knowledge about out-of-plane normal and shear stresses which are difficult to obtain experimentally. To remedy the problem, a novel approach was developed in which the microstructural properties of AA7075-Osheet obtained from Electron Backscattered Diffraction (EBSD) images were utilized to generate a three-dimensional (3D) representative volume element (RVE). Then, by applying the microstructure-based crystal plasticity (CP) material model to the 3D RVE, it was possible to perform computational experiments to calculate the out-of-plane normal and shear stresses required for the calibration of the Yld2004-18p yield function.

Finally, to model the single point incremental forming (SPIF) of 7075-O aluminum alloy sheet, two different calibrated yield functions namely; Hill’s 1948 and Yld2004-18p were used. A detailed comparison of the two yield functions’ predictions was made with respect to different parameters, such as the tool force and moment, part thickness distribution, stress and strain tensor components, and the effective plastic strain distribution.

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