The effect of single, shaped surface flaws on ductility in cast aluminum dog bone specimens in uniaxial tension
Date
2017
Authors
Wardwell, Scott L., author
Mahmoud, Hussam, advisor
Atadero, Rebecca, committee member
Shuler, Scott, committee member
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Abstract
Ductile fracture of structural, metallic alloys is of great interest to the engineering community. This interest has sparked many attempts in an effort to describe the fracture process for these ductile materials. The theory that stands out is that ductile fracture is driven by the process of void nucleation, growth and coalescence which, as the name suggests, allows voids to be created through nucleation, then follows their growth and coalescence until material failure occurs. In this process, a damage criterion is often selected and used to model and predict how ductile fracture will occur. While this modeling yields results with enough accuracy to be useable in practical applications, it relies on some initial idealized void geometry. These geometries are usually of cylindrical or spherical nature and do not capture the essence of the actual void geometry of real materials. Surface flaws, on the other hand, are often modeled to mimic their actual appearance in real materials. This being the case, little research has been conducted on actual void geometry or highly specific, three-dimensional surface flaw geometry. This study explores these relatively untouched regions of geometrical interest and their effect on the ductile fracture process through physical testing of specifically shaped surface flaws on structural grade aluminum. Additionally, aluminum demonstrates unique properties with respect to ductility. Other ductile materials often yield in tension then continue to stretch and withstand additional loading up to some maximum material strength then stretch more until eventual failure. Many commercially available grades of aluminum however, fail almost immediately after reaching their maximum material strength. The results from this study are compared so that the effects of the specific shapes on ductility can be seen. The results suggest that, depending on the definition of ductility, it may be possible to easily increase material performance for ductile materials, which demonstrate the unique ductility profile seen in aluminum, by introducing specifically shaped surface flaws.
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Subject
cast
flaw
tension
ductile
aluminum
fracture