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Research Papers

Crack Tip Fields in a Single Edge Notched Aluminum Single Crystal Specimen

[+] Author and Article Information
Swapnil D. Patil, R. Narasimhan

Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India

P. Biswas

 India Science Lab, General Motors Corporation, Bangalore 560066, India

R. K. Mishra

 General Motors Corporation, 30500 Mound Road, Warren, MI 48090

J. Eng. Mater. Technol 130(2), 021013 (Mar 13, 2008) (11 pages) doi:10.1115/1.2884330 History: Received July 20, 2007; Revised January 25, 2008; Published March 13, 2008

We report a combined experimental and computational study of a low constraint aluminum single crystal fracture geometry and investigate the near-tip stress and strain fields. To this end, a single edge notched tensile (SENT) specimen is considered. A notch, with a radius of 50μm, is taken to lie in the (010) plane and its front is aligned along the [101] direction. Experiments are conducted by subjecting the specimen to tensile loading using a special fixture inside a scanning electron microscope chamber. Both SEM micrographs and electron back-scattered diffraction (EBSD) maps are obtained from the near-tip region. The experiments are complemented by performing 3D and 2D plane strain finite element simulations within a continuum crystal plasticity framework assuming an isotropic hardening response characterized by the Pierce–Asaro–Needleman model. The simulations show a distinct slip band forming at about 55deg with respect to the notch line corresponding to slip on (11¯1)[011] system, which corroborates well with experimental data. Furthermore, two kink bands occur at about 45deg and 90deg with respect to the notch line within which large rotations in the crystal orientation take place. These predictions are in good agreement with the EBSD observations. Finally, the near-tip angular variations of the 3D stress and plastic strain fields in the low constraint SENT fracture geometry are examined in detail.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram showing Mode I plane strain geometry. Families of straight lines are traces of slip plane intersections with the plane of deformation (X3=constant). S(α) and N(α) are unit vectors along and normal to the slip line trace for system α.

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Figure 3

Two-dimensional schematic diagram of the SENT fracture specimen along with boundary conditions

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Figure 4

Scanning electron micrographs of the region near the notch tip on the free surface of Al single crystal SENT specimen at various stages of deformation pertaining to load point displacement Δ of (a) 0mm, (b) 0.1mm, (c) 0.15mm, and (d) 0.2mm

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Figure 5

(a) IPF map obtained from EBSD data at specimen free surface, showing the occurrence of two sets of kink bands emanating from notch tip at angles of about ±45deg and ±90deg to the notch line. (b) The IPF color code for the EBSD.

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Figure 6

Load versus displacement curves obtained from 2D plane strain and 3D finite element analysis along with experimental data

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Figure 7

Fringe contours of plastic slip γ on dominant slip system (11¯1)[110], computed from 3D finite element analysis on the specimen free surface at Δ=0.02mm superposed on the experimental scanning electron micrograph

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Figure 8

Fringe contours of misorientation angle ϕ on the free surface of the specimen determined from 3D finite element analysis at Δ=0.02mm

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Figure 9

Fringe contour plots of plastic slip γ on (11¯1)[110] slip system obtained from 3D analysis: (a) at the center plane and Δ=0.02mm, and at the free surface of the specimen corresponding to (b) Δ=0.02mm, (c) Δ=0.06mm, and (d) Δ=0.2mm

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Figure 10

Fringe contour plots of maximum principal logarithmic plastic strain log(λ1p) obtained from the 3D analysis corresponding to Δ=0.02mm: (a) at the center plane and (b) at the free surface of the specimen

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Figure 11

Angular variations of normalized in-plane components of the Kirchhoff stress tensor at r∕h=0.125 obtained from the 2D plane strain and the 3D analysis at center plane of the specimen corresponding to Δ=0.02mm: (a) τ11∕τ0, (b) τ12∕τ0, and (c) τ22∕τ0

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Figure 12

Angular variations of plastic slip γ on all 12 slip systems (or six conjugate pairs) at r∕h=0.25 obtained from the 3D analysis at the center plane of the specimen corresponding to Δ=0.2mm

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Figure 13

Angular variations of maximum principal logarithmic plastic strain log(λ1p) at r∕h=0.125 obtained from the 2D plane strain analysis and the 3D analysis at the specimen center plane and free surface corresponding to Δ=0.02mm

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Figure 2

Slip line sectors in the asymptotic solution proposed by Rice (1) for the Mode I plane strain geometry depicted in Fig. 1 showing constant stress Sectors A, B, C, and D along with stress discontinuity lines

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