Ductile Fracture of Metal Materials

There are many ways for engineering materials to fail, and fracture is one of them. Other failure modes include deformation, wear, corrosion, etc. Fracture failure is the most dangerous and often causes casualties or major economic losses.

Fracture is also divided into ductile fracture and brittle fracture. This classification is based on whether there is plastic deformation before the fracture.

If there is macroscopic plastic deformation before the fracture, it is called ductile fracture or ductile fracture; if there is no obvious plastic deformation, it is called brittle fracture.

Ductile fracture is less dangerous than brittle fracture. Because if overloaded or subjected to excessive force, the component will first undergo plastic deformation before the fracture, and because of the plastic deformation, work hardening will occur, and the resistance to fracture will increase, so ductile fracture has signs and a certain emergency treatment time.

Brittle fracture has no signs. When the force is not too large, it will suddenly break. There is no reaction time when the accident occurs, so the harm of brittle fracture is much greater.

Today, let's mainly talk about ductile fracture.

So, what is ductile fracture?

The so-called ductile fracture is a fracture mode in which plastic deformation plays a dominant role in the fracture process, including shearing and microporous aggregation fracture.

Shearing means that the slip develops along the slip plane at 45° to the force direction until the sample separates along the slip plane. Shearing also has two manifestations.

One is that when tensile plastic deformation occurs, only one slip system is activated to form a blade-shaped fracture. This type of fracture often occurs in single crystal materials.

The other is that multi-system slip occurs during stretching, and each slip system deforms in coordination, continuously and uniformly necks. When the necking reaches zero cross-sectional area, the sample breaks and forms a double cone fracture. This type of fracture often appears in relatively pure polycrystalline materials.

Microporous aggregation fracture means that obvious plastic deformation and necking will also occur before fracture, and a cup-cone fracture will be formed during fracture.

For general industrial metal materials, microporous aggregation fracture will mostly occur during ductile fracture. The generation and aggregation of micropores are related to inclusions and second phases in the material. Because the plasticity of inclusions and the second phase is different from that of the matrix, they not only become the site of micropores, but also hinder the smooth progress of slip. The combined effect of these factors makes the macroscopic morphology of the fracture a cup-cone shape.

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