ISSN:
1662-7482
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
This work analyses those size effects that are encountered first upon downscaling,including grain boundary effects, free surface effects, grain statistics effects. The separate influenceof first-order effects was carefully investigated from uniaxial tensile tests on high-purity aluminumspecimens with a well-defined microstructure of through-thickness grains, whereby the total numberof grains in the cross-section was reduced towards a single grain in a cross-section by, first,decreasing the film thickness and, second, for specimens with through-thickness grains decreasingthe specimen width. In addition, 3D dislocation-field strain gradient plasticity simulations wereemployed to analyze the intrinsic size effects, using the grain size and texture as measuredexperimentally.The work shows that for miniaturized structures with a limited number of columnar grains a uniqueHall-Petch relation does not exist, even though a grain boundary effect, i.e. a decrease in stress level(at a given strain) for decreasing grain boundary area per unit volume, is clearly present. When themicrostructure is kept constant upon miniaturization, the free surface per unit area increases causingthe stress level of the structure to decrease, the effect of which increases towards a single grain inthe cross-section. In addition, the work shows that grain statistics effects also contribute to observedweakening, due to insufficient compensation of local (weaker) material properties by thesurrounding material (i.e. grains). Finally, grain statistics also significantly increase the statisticalvariation in mechanical properties for small-sized structures, an effect that is especially importantfor the reliability of miniature components. The separate influence of these first-order effects as wellas their interplay are explained in terms of the movement of the dislocations upon plastic flow
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/01/38/transtech_doi~10.4028%252Fwww.scientific.net%252FAMM.13-14.183.pdf
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