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TECHNICAL PAPERS

# Modeling the Influence of Material Structure on Deformation Induced Surface Roughening in AA7050 Thick Plate

[+] Author and Article Information
T. J. Turner

Materials and Manufacturing Directorate, Air Force Research Laboratory, 2230 10th Street, Wright-Patterson AFB, OH 45433-7817

M. P. Miller

Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853

J. Eng. Mater. Technol 129(3), 367-379 (Nov 14, 2006) (13 pages) doi:10.1115/1.2744395 History: Received November 15, 2005; Revised November 14, 2006

## Abstract

A methodology for incorporating a description of material structure into a finite element formulation is presented. This work describes an experiment/simulation - based methodology for characterizing attributes of material structure, and then incorporating those attributes into a modeling framework. The modeling framework was used to study the development of deformation induced surface roughening in thin sheets machined from AA 7050 thick plate. Predicting this roughening phenomenon necessitates the quantification and representation of material structure and processes that exist over several size scales. Electron backscatter diffraction experiments were used for material structure characterization, which included crystallographic texture, distributions in grain sizes, and a distribution in intragrain misorientation. These distributions in structure were incorporated in digital microstructures which represented virtual specimens composed of finite element-discretized crystals. A continuum slip-polycrystal plasticity model was coupled with the digital microstructures to study the differences in roughening seen in specimens deformed along the rolling direction and transverse direction of the plate material. The success of these simulations build additional insight into how to incorporate material structure into deformation simulations, and build representative virtual specimens that can be used to study the complicated processes that underlie deformation mechanics in polycrystalline materials.

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## Figures

Figure 6

Normalized power spectral decomposition (PSD) curves for surface profiles of the: (a) RD specimen in the RD direction; (b) the RD specimen in the TD direction; (c) the TD specimen in the RD direction; and (d) the TD specimen in the TD direction

Figure 7

Optical micrograph of the grain structure at the T/2 plane of the 6.35-cm-thick AA 7050 plate prepared with electrolytic Barker’s etch

Figure 8

Schematic showing the setup of the grain size measurements using line scans with the EBSD technique

Figure 1

Tensile specimens machined from the centerplane (T/2) of a 6.35-cm-thick plate showing deformation induced surface roughness

Figure 2

A schematic showing the fabrication of the tensile dogbone specimens from the 6.35-cm-thick AA 7050 plate

Figure 3

The effective stress strain response of the RD and TD tensile specimens

Figure 4

Post-deformation surface roughness data for the: (a) RD; and (b) the TD specimens. Simulated surface roughness for the (c) RD tensile specimens and (d) TD tensile specimen.

Figure 5

The autocorrelation function (ACF) for surface profiles of the: (a) RD specimen in the RD direction; (b) the RD specimen in the TD direction; (c) the TD specimen in the RD direction; and (d) the TD specimen in the TD direction

Figure 13

Creation of the digital microstructure through a modified Voronoi construction

Figure 14

A digital microstructure created with an elongated grain structure

Figure 12

(a) Determining the applied deformation to the FEM digital microstructure and (b) the boundary conditions applied to the FEM digital microstructures when modeling the RD tensile specimen

Figure 9

The grain size distributions for the 12-layer finite element model compared to the experimentally measured distributions for: (a) the RD; (b) TD; and (c) ND directions

Figure 10

The crystallographic texture (in multiple times random, m.u.d.) of the experimental AA 7050 material measured by EBSD at the T/2

Figure 11

The digital microstructure where the color map is an indication of orientation for 48,000 elements

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