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Research Papers

Transition of Crack Propagation Path Under Varied Levels of Load in Bimodal Grain Size Al-Mg Alloy

[+] Author and Article Information
Leila Ladani

Mechanical Engineering Department,  The University of Alabama, Tuscaloosa, AL 35487lladani@eng.ua.edu

Steven Nelson

Mechanical Engineering Department,  The University of Alabama, Tuscaloosa, AL 35487steven.nelson@aggiemail.usu.edu

J. Eng. Mater. Technol 133(4), 041017 (Oct 27, 2011) (6 pages) doi:10.1115/1.4004693 History: Received March 11, 2011; Accepted July 15, 2011; Published October 27, 2011; Online October 27, 2011

Mechanical fatigue crack nucleation and propagation is modeled in bimodal grain size aluminum alloy. A multiscale modeling approach in conjunction with a continuum based damage modeling technique, successive initiation, is used to determine microstructural site of crack nucleation and its propagation through different regions of the materials. Analyses conducted for material with different coarse grain volume ratios under different load amplitudes showed that damage initiates at the interface of coarse grains and the ultrafine grain matrix. It propagates initially through coarse grains with higher initial damage rate. Once the coarse grains lose their load bearing capacity, the load is transferred to the ultrafine matrix and it fails rather quickly. Comparison between different large grain volume ratios shows that the small distance between large grains at high coarse grain volume ratios facilitates crack bridging between coarse grains and results in very high crack propagation rate in coarse grains which eventually results in catastrophic failure of the whole structure.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

S-N fatigue curves for bimodal grain size aluminum alloy

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Figure 2

Global–local modeling approach used for microstructural finite element modeling

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Figure 3

Cyclic stress–strain curve for UFG, 15% large grain and 100% large grain Al–Mg bimodal grain size

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Figure 4

Crack nucleation and propagation in four intermediate steps of the simulation for an ISA of 0.05

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Figure 5

Crack nucleation and propagation in four intermediate steps of the simulation for an ISA of 0.1

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Figure 6

Crack nucleation and propagation in four intermediate steps of the simulation for an ISA of 0.2

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Figure 7

Crack nucleation and propagation in four intermediate steps of the simulation for an ISA of 0.4

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Figure 8

Crack length as function of number of cycles for total crack, UFG crack and CG crack for two different ISAs for CG volume ratio of 10%

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Figure 9

Average crack propagation rate for CGs volume ratio of 10%

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Figure 10

Average crack propagation rate for CG volume ratio of 25%

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Figure 11

Crack propagation in 25% CG volume ratio

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