What Does Ductile Fracture Mean?
A ductile fracture is a type of fracture characterized by extensive plastic deformation or necking. This usually occurs prior to the actual fracture.
In a ductile fracture, there is absorption of massive amounts of energy and a slower propagation before the fracture occurs as compared to a brittle fracture.
All fracture processes involve two steps, crack formation and propagation, which are responses to imposed stress. The rate of the fracture is highly dependent on the mechanics of the crack propagation. Cracks that occur in ductile materials are said to be stable, meaning they are able to resist extension without any increase in stress. However, in brittle materials, cracks are unstable, which means that the crack propagation, once started, continues spontaneously without an increase in stress level.
By understanding ductile fractures, engineers are able to develop more dependable and safer industrial products and materials. For example, ductility is a desirable property in high temperature and high-pressure applications in reactor plants due to the added stresses on the metals. High ductility in these applications helps to greatly reduce the possibility of a sudden brittle fracture.
Corrosionpedia Explains Ductile Fracture
A fracture is one of the most crucial concepts in terms of material engineering. In general, a fracture is one body going through separation due to imposed stresses. The term ductile rupture refers to the failure of highly ductile materials, and in such cases, materials pull apart instead of cracking.
Almost all engineering materials undergo only two types of fracture modes: brittle fracture and ductile fracture.
Ductile materials exhibit massive amounts of plastic buckling or deformation in comparison to brittle materials. In a ductile fracture, the crack grows at a slow pace and is accompanied by a great deal of plastic deformation. In this case, the crack does not expand except when high levels of stress are present.
A ductile fracture in metallic alloys and metals usually originates from the growth, initiation and coalescence of microscopic voids that occurs during plastic deformation. The void nucleation usually happens at the interfaces of second-phase particles. At these interfaces disassociation is regarded as the dominant mechanism of void nucleation. Upon void nucleation, there’s further plastic deformation and enlargement of the size of voids and distortion in the shape, which can be referred to as void growth. As theses voids enlarge and distort substantially with plastic deformation, adjacent voids link up with each other due to localization of the plastic strain in the intervoid matrix that forms the final fracture surface. Void coalescence can be monitored directly by SEM analysis from fracture surfaces because void coalescence is the final stage in ductile fracture.
Under the view of a microscope, the surfaces of materials with ductile fractures appear irregular and rough, and exhibit some dimpling. But in almost all design situations, materials that exhibit ductile fracture are preferable for various reasons, including:
- Ductile materials elastically deform, slowing the fracture process and allowing more time to correct problems
- Higher amounts of energy strain are required to deform a ductile material
- Ductile materials are forgiving, and any error in the design process does not immediately result in a catastrophic failure