Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers



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Last updated: August 30, 2017

What Does Ductility Mean?

Ductility is the measure of a material's ability to plastically deform without fracturing when placed under a tensile stress that exceeds its yield strength. High ductility indicates that a material will be more apt to deform and not break whereas low ductility indicates that a material is brittle and will fracture before deforming under a tensile load. Ductility depends largely on a material's chemical composition, crystalline structure and the temperature at which the ductility is being measured.

Steel tends to be quite ductile which allows it to accommodate local stress concentrations. Materials such as glass are brittle and cannot accommodate stress due to their lack of ductility, causing them to fracture easily. Ductile materials deform elasticity with stress, at first. When the stress increases too far, the material reaches the elastic limit. Stress following the elastic limit causes plastic deformation which is permanent.

Ductility is a mechanical property that describes how readily a material can be drawn into a wire and sustain plastic deformation without failure. A material that is said to have high ductility is ductile, while one with low ductility is brittle.


Corrosionpedia Explains Ductility

Ductility is not the same as malleability. Ductility is a measure of material deformation under a tensile stress, whereas malleability is a measure of material deformation under compressive stress. A material does not necessarily have to have both high ductility and high malleability. It could have high malleability and low ductility.

Metals that have high ductility include gold, platinum, silver and iron. Some low ductility metals include tungsten and steels with high amounts of carbon. Polymers are usually ductile; however there are brittle polymers available. Ceramics are typically brittle.

The temperature of a material will alter its ductility. Metals have a ductile-to-brittle transition temperature. For polymers this is called a glass transition temperature. The exact temperature is different for every material, but once it is reached, ductility is vastly reduced and the material becomes brittle. The ductile-to-brittle transition temperature or glass transition temperature of a material is an important consideration for materials subject to extreme cold.

Gold is one of the most ductile metals; one ounce of gold could be drawn into a wire 50 miles (80km) long. Some metals are highly ductile because of their metallic bonds that allow electrons to be delocalized and shared between atoms. They also depend on valence electrons for their metallic characteristics, making it possible for their atoms to move easily past each other.

The connection between the number of electron shells of an atom and the material's ductility is such that the greater the number of electron shells, the higher the ductility. The valence electrons in the element also determine ductility. Gold, lead and platinum all have six electron shells and all three of these metals display very high ductility. Iron, manganese and chromium are metals that each have four electron shells and have lower ductility. Beryllium is very brittle with only two electron shells. Other factors that affect ductility are temperature, grain size and crystal structure. (Also Read: The Crystalline Structure of Metals)

In materials science, ductility is the ability of a material to withstand large plastic deformations before failure. It is one of the very important characteristics that is considered during design. Ductility may be expressed as percent elongation or percent area reduction from a tensile test.

Ductility is vital for knowing how much load a structure can take — especially large pressure changes, earthquakes or hurricanes — without meeting a sudden failure or collapse. In the case of metals, the ductile-to-brittle transition temperature is the limit at which metals become brittle. Specific nickel-based steels have better resistance to this failure mode.


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