Uniaxial Stress Deformation Experiment for Validation of 3-D Dislocation Dynamics Simulations

[+] Author and Article Information
David H. Lassila, Mary M. LeBlanc, Gregory J. Kay

Lawrence Livermore National Laboratory, P.O. Box 808, L-113, Livermore, CA 94551-0808

J. Eng. Mater. Technol 124(3), 290-296 (Jun 10, 2002) (7 pages) doi:10.1115/1.1479177 History: Received January 17, 2002; Received February 15, 2002; Online June 10, 2002
Copyright © 2002 by ASME
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Single crystal test sample as placed in the laboratory reference frame. The sample has a square cross-section 5.5 mm on a side with a corner radius of 1 mm. As shown, the [2,9̄, 20̄] direction points in the positive z direction and the [1,−2,1] direction points in the positive y direction. The four faces of the sample are identified as “a” through “d.” The primary slip plane and slip directions are also labeled.
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A schematic representation of the test apparatus. On the left is the overall view showing the loading actuator, load cell and subpress. On the right is a detail view of the sample, loading platen arrangement, and displacement sensors.
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Axial stress-strain curve for a Mo single crystal. The stress is the axial stress calculated from the load measurement; strain is the averaged value of the three extensometer strains (measured across the platens).
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The tilt of the top of the sample as calculated from the three extensometers. On the polar plot, the radial (r) axis represents the magnitude of the tilt in degrees, i.e. the angular difference between a line perpendicular to the top of the tilted sample and the z axis. The angular axis (θ) shows the direction of the tilt where the plot center is the z axis in the laboratory reference frame and the line from (0,0 deg) to (0,90 deg) is the y axis.
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The translation of the bottom of the test sample as measured by the laser sensors. The bottom of the sample translated linearly a total of approximately 150 μm in a combination of the positive x and negative y directions.
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Stress-strain curves for a Mo crystal showing a comparison of the strains on opposite faces of the sample. As labeled, the strains shown are for the coordinate axis directions x,y, and z and for the shear strains γxz and γyz. The strains for the “c” and “a” faces are shown in (a) above; the strains for the “b” and “d” faces are shown in (b) above.
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The measured translation platen motion is shown for a polycrystalline (isotropic) Cu sample and a Mo single crystal. The motion of the platen predicted by the strain gage data for the Mo crystal is also shown.
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A 3-D FEM calculation shows the effect on the axial sample stress of translating the bottom of the sample the distance measured in the experiment (150 μm).
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A comparison of the stress-strain curves for two different Mo single crystal compression experiments. The strains are as measured from the gages in the axial (z) (gage 2), and ±45 deg (gage 1 and 3) directions.




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