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Research Papers

Scaling of Strength of Metal-Composite Joints—Part I: Experimental Investigation

[+] Author and Article Information
Qiang Yu

Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL 60208qiangyu@northwestern.edu

Zdeněk P. Bažant1

Department of Civil and Materials Science, Northwestern University, Evanston, IL 60208z-bazant@northwestern.edu

John Bayldon

Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL 60208j-bayldon@northwestern.edu

Jia-Liang Le

Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL 60208jialiang-le@northwestern.edu

Ferhun C. Caner2

Associate Professor of the Institute of Energy Technologies,Universitat Politècnica de Catalunyaferhun.caner@upc.edu

Wei Heok Ng

Department of Aerospace Engineering and Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2122whn@umich.edu

Anthony M. Waas

Department of Aerospace Engineering and Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2122dcw@umich.edu

Isaac M. Daniel

Department of Civil Engineering and Mechanical Engineering, Northwestern University, Evanston, IL 60208imdaniel@northwestern.edu

1

Corresponding author. Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, CEE/A135, Evanston, IL 60208.

2

Visiting scholar at Northwestern University on leave from UPC.

J. Appl. Mech 77(1), 011011 (Oct 01, 2009) (8 pages) doi:10.1115/1.3172254 History: Received October 29, 2008; Revised March 04, 2009; Published October 01, 2009

Knowledge of the size effect on the strength of hybrid bimaterial joints of steel and fiber composites is important for new designs of large lightweight ships, large fuel-efficient aircrafts, and lightweight crashworthy automobiles. Three series of scaled geometrically similar specimens of symmetric double-lap joints with a rather broad size range (1:12) are manufactured. The specimens are tested to failure under tensile displacement-controlled loading, and at rates that ensure the peak load to be reached within approximately the same time. Two series, in which the laminate is fiberglass G-10/FR4, are tested at Northwestern University, and the third series, in which the laminate consists of NCT 301 carbon fibers, is tested at the University of Michigan. Except for the smallest specimens in test series I, all the specimens fail by propagation of interface fracture initiating at the bimaterial corner. All the specimens fail dynamically right after reaching the maximum load. This observation confirms high brittleness of the interface failure. Thus, it is not surprising that the experiments reveal a marked size effect, which leads to a 52% reduction in nominal interface shear strength. As far as the inevitable scatter permits it to see, the experimentally observed nominal strength values agree with the theoretical size effect derived in Part II of this study, where the size exponent of the theoretical large-size asymptotic power law is found to be −0.459 for series I and II, and −0.486 for series III.

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Figures

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Figure 1

Geometry of double-lap hybrid joint

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Figure 2

Specimens of (a) test series I, (b) test series II, and (c) test series III

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Figure 3

Tests giving basic material properties of laminates: (a) tensile test, (b) through-thickness compressive test, and (c) V-notched beam test

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Figure 4

(a) Test setup at Northwestern University; (b) test setup at the University of Michigan

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Figure 5

Load-displacement deformation curves (a) of test series I, (b) of test series II, (c) of test series III, and (d) tensile fracture in laminates and shear fracture in bimaterial interface

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Figure 6

Measured nominal strength values compared with optimum fit by size effect formula (solid curve): (a) test series I and (b) test series II

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Figure 7

Measured nominal strength of test series III compared with optimum fit by size effect formula

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Figure 8

(a) Delamination pattern observed in test series II, (b) differences in readings of opposite LVDT gauges in test series II, and (c) strain differences at opposite specimen sides recorded in test series III

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