Understanding The Ductile and Brittle Nature of Materials

As you know from design engineering or in mechanical engineering lessons such as strength of materials, materials science, etc. ductile and brittle features of materials are very important. In an engineering design, the designer must consider the ductile or brittle nature of materials such as metals. By looking at very basic graphs and information of material, you can estimate lots of kinds of physical and engineering features of a material such as the ductility and brittleness of materials mentioned here. 

What Is The Ductility?

Stress-strain graphs of ductile and brittle materials.

The ductility of an engineering material is the ability of that material whether can undergo to plastic deformation. If an engineering material undergoes plastic deformation under certain loads or stresses, this material is considered a ductile material. 

Schaum’s Outline of Statics and Strength of Materials (Schaum’s)

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As you know, plastic deformation starts from the tensile limit of the material. Approximately after the tensile limit, plastic deformation starts if an engineering material shows ductile nature. 

Ductility has levels. Different engineering materials have different ductility values. For example, low carbon steels have very high ductility which can undergo very high plastic deformation rates. But ceramic materials have very low ductility or zero ductility so there is no plastic deformation before the fracture. 

Brittleness On Engineering Materials

The brittle nature of the engineering materials is considered as there is no plastic deformation up to fracture of that material under certain loads or stresses. You can understand that brittleness and ductility are the opposite features of materials. Between these opposite sides, materials are placed in certain places. 

A brittle material is not ductile material and a ductile material is not a brittle material. Maybe the most brittle engineering materials are ceramics which do not show any plastic deformation. If the stress of load is applied to a ceramic part, that part will fracture instantly after a level of stress. 

At the tensile limit, brittle materials fracture. When the localized stress reaches that tensile limit of the brittle material, abrupt fracture takes place. 

Ductility and Brittleness of Materials In Design View

Ductile(left) and brittle(right) fractures of tensile test specimens(Image Source: https://www.eurekamagazine.co.uk/design-engineering-news/ductile-high-strength-steel-developed-in-wmg-project/156839/).

If you are a designer, you need to consider the ductile and brittle nature of materials in terms of their properties. In most engineering design procedures that include static and dynamic loads, a sufficient amount of ductility is desired. Because, before the fracture, the material shows visual plastic deformation that warns about the fracture. Fracture does not take place abruptly. So, the predictability of fracture for ductile materials is better than the brittle materials. 

You may make a safety stress design from a brittle material by using its tensile limit. But, it is not predictable that fracture will take place because of complex reasons such as microvoids or microcracks in the structure of the brittle part. 

Brittle materials are used in engineering design also. But in general, they are used in applications where any engineering stresses are in view such as dynamic loads. For example, brittle ceramic materials are used for low heat emissivity applications where good insulations are required. 

Brittle to Ductile Transition

It is a very important phenomenon for most metals and metal alloys. With the changing temperature, the ductile and brittle nature of materials change. For example, tungsten is a brittle material at room temperature but it is a very ductile material in elevated temperatures. 

So, you need to consider the external conditions to assess the brittleness or ductility of engineering material. 

Conclusion

These are the general considerations about the ductile and brittle natures of engineering materials, in engineering design procedures. 

Do not forget to leave your comments and questions below about the ductility and brittleness of engineering materials! 

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