Ductile Damage Dance-Off

Ductile Fracture experiences substantial plastic deformation before fracturing occurs. As can be seen above, the highly ductile sample has an area reduction of 100%, down to a single point before fracturing.

This fracturing type is stable, meaning the sample will resist further expansion unless a force is continuing to be applied to the fracture site.

Stages of Fracture

Initial Necking

The ductile sample undergoes uniform elongation until it reaches it's yield point, at this point the sample is stretched plastically. It is at this point that necking occurs within the sample, where the diameter shrinks as the sample is stretched further. This represents a large concentration of strain in a small region in the sample.

Micro-void formation

Due to heterogeneity (un-uniformity of the sample), micro-voids (small cavities) form within the sample. These occur mainly at sites of stress concentration within the material, such as inclusions, intermetalic or secondary phases and along grain boundaries. Within the primary crystalline structure, stress concentrations typically occur though vacancies, interstitial atoms and interstitial or substitution impurity atoms, which can aid in the formation of micro-voids.

Cavity Coalescence

As force continues to be applied to the material, the deformation continues to grow. The micro-voids which were formed start to grow larger and join together to form larger voids. The coalescence of these voids forms an elliptical crack which runs perpendicular to the applied stress.

Crack Propagation

As the force on the material continues, the elliptical void propagates to the edge of the material. At this point the deformation is at 45 degrees to the axis of the applied force.

Final Shear

When the material finally shears, it can form a cup and cone structure. where the elliptical cavity used to be. The surfaces of the crack may have a fibrous and irregular appearance, which can be indicative of plastic deformation.