Multiscale Experiments: State of the Art and Remaining Challenges

[+] Author and Article Information
R. Agrawal

Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3111

H. D. Espinosa1

Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3111espinosa@northwestern.edu


Corresponding author.

J. Eng. Mater. Technol 131(4), 041208 (Sep 01, 2009) (15 pages) doi:10.1115/1.3183782 History: Received February 24, 2009; Revised June 10, 2009; Published September 01, 2009

In this article we review recent advances in experimental techniques for the mechanical characterization of materials and structures at various length scales with an emphasis in the submicron- and nanoregime. Advantages and disadvantages of various approaches are discussed to highlight the need for carefully designed experiments and rigorous analysis of experimentally obtained data to yield unambiguous findings. By examining in depth a few case studies we demonstrate that the development of robust and innovative experimentation is crucial for the advancement of theoretical frameworks, assessment of model predictive capabilities, and discovery of new physical phenomena.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

A schematic summarizing the main experimental techniques developed for testing thin films and the corresponding theoretical models

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Figure 3

(a1) A SEM image of a 20 μm diameter Ni pillar showing slip events at ∼4% strain an engineering stress of ∼50 MPa; (a2) SEM image of a 5 μm diameter Ni pillar after testing at ∼19% strain where a rapid burst of deformation occurred in less that 0.2 s. Engineering stress as high as 130 MPa was observed; (b1,2) SEM image of a 660 nm Au pillar before and after deformation. In these experiments, yield stress as high as 500 MPa was observed for a 400 nm pillar; and (c1,2) TEM images acquired during in situ TEM nanoindentation tests on a 160 nm diameter Ni nanopillars. Before the test (c1), the nanopillar had high dislocation density, which disappeared after first loading. Stresses as high as 1.0 GPa were reported. (Permissions: (a) reprinted with permission from Uchic (56)© 2004 American Association for the Advancement of Science; (b) Reprinted with permission from Greer (57)© 2005 Acta Materialia Inc. published by Elsevier Ltd.; and (c) reprinted with permission from Shan (58)© 2008 Nature Publishing Group).

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Figure 4

(a) Experimentally obtained stress-strain behavior of gold pillars under compression, showing the increasing yield stress with decreasing diameter; (b) Computationally obtained stress-strain plots for 400 nm pillars with same dislocation density, but different initial dislocation configurations; (c) a series of images showing the dislocation evolution associated with strain bursts (see text for detailed explanation) (Permissions: (a) reprinted with permission from Greer and Nix (62), http://link.aps.org/doi/10.1103/PhysRevB.73.245410. © 2006 The American Physical Society; (b) reprinted with permission from Tang (60), http://link.aps.org/doi/10.1103/PhysRevLett.100.185503. © 2008 The American Physical Society).

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Figure 5

Summary of Young’s modulus of ZnO nanostructures as a function of characteristic size obtained by different experimental techniques

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Figure 6

(a) SEM micrographs demonstrating the in situ thermal vibration tests. 1—freestanding nanotubes fixed at one end; 2—first mode of resonance; 3—second mode of resonance; (b) schematic representation of AFM-based three-point bending tests in lateral force mode; (c) schematic representation of AFM-based three-point bending tests in contact mode. Top figure shows the AFM image of a SWNT rope suspended over a polished alumina ultrafiltration membrane; (d) schematic representation showing the setup for in situ tension tests on an individual MWNT using two calibrated AFM probes. (Permissions: (a) reprinted with permission from Poncharal (71). © 1999 American Association for the Advancement of Science; (c) reprinted with permission from Salvetat (72), http://link.aps.org/doi/10.1103/PhysRevLett.82.944. © 1999 American Physical Society).

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Figure 7

(a) SEM micrograph of MEMS-based nanoscale-material testing system to perform in situ TEM tests; (b) SEM image of a ZnO nanowire mounted on the n-MTS with e-beam induced deposition of platinum to fix the two ends; (c1,2) TEM images of the ZnO NW taken during a tensile test at 0% and ∼2.5% strain. Inset shows the corresponding diffraction patterns; (c3) Intensity analysis of the diffraction patters shown in (c1) and (c2) along [0001] direction to measure the change in lattice constant; (d1) Contours of radial displacements, for nanowires of different diameters, after energy minimization; (d2) Young’s modulus normalized with bulk modulus, as a function of normalized radial coordinate in each atomic layer. The shell thickness, s, is indicated. (Reprinted with permission from Agrawal (78). © 2008 American Chemical Society).

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Figure 8

(a1) TEM image of a MWNT after fracture; (a2,3) intensity profiles taken along the paths E and F in (a1) to count the number of shells before and after failure. (b) Stress-strain response comparing the experimental data with theoretical predictions; (c) computational calculation of load transferred to the inner shell of a double-walled nanotubes as a function of the number of cross-links. (Reprinted with permission from Peng (93). © 2008 Nature Publishing Group).

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Figure 2

Schematic showing plain strain bulge test before and after application of uniform pressure; (b) schematics of membrane deflection experiment; (c) a SEM micrograph of the MEMS-based testing setup; (d) a low magnification TEM image showing the in situnanoindentation (Permissions: (a) reprinted with permission from Xiang and Vlassak (25)© 2006 Elsevier Ltd.; (c) reprinted with permission from Haque and Saif (31)© 2002 Acta Materialia Inc. published by Elsevier Science Ltd.; and (d) reprinted with permission from Minor (32)© 2006 Nature Publishing Group)




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