(Georgia Institute of Technology, 2017)
Lanning, Wade R.; Javaid, Syed S.; Muhlstein, Christopher L.
The well-known trade-off between strength and fracture toughness in bulk specimens is often
used to explain the low fracture toughness of very thin ductile face-centered cubic (FCC) metal
specimens, but this interpretation contradicts the relative length scales of thickness-dependent
strength and thickness-dependent fracture toughness. This study uses the concept of similitude
to demonstrate that linear elastic fracture mechanics (LEFM) analysis of 25:4 μm thick annealed
aluminum is invalid, though the resulting fracture toughness measurements fit well with the existing
literature and idea of a strength/fracture toughness trade-off. Similarly, a elastic plastic fracture
mechanics (EPFM) analysis is sensitive to out-of-plane deformation which cannot be practically
eliminated or corrected for with a model. However a plastic collapse analysis using a critical net
section stress criterion is demonstrably valid by the concept of similitude, is insensitive to out of
plane deformation, and agrees with the evidence of extensive plasticity in the fracture surfaces.