Ductility
The Main Idea
Ductility is a solids ability to deform under tensile stress. It is similar to malleability, which characterizes a materials ability to deform under an applied stress. Both of these are plastic properties of materials. While they are often similar, sometimes a materials ductility is independent from its malleability. Materials with metallic bond have much higher ductility's du to the mobile electrons that tend to deform, rather than fracture. Therefore the most common ductile materials are steel, copper, gold and aluminum. Ductility is an important property in material science and metal-working industries, where solids are deformed and molded with outside forces.
Environmental factors can also affect the ductility of a material. A temperature increase causes a material to stretch, and thus increases ductility. A temperature decreases leads to brittle and fragile behavior of the material and as such decreases ductility. Percent Reduction of Area (formula below) is a better accepted form for measuring ductility of a material.
The Ductile - Brittle Transition Temperature is the temperature at which the fracture energy passes below a predetermined value (typically 40 J). The Ductile - Brittle Transition Temperature is an important consideration when determining which material to select, when said material is subjected to mechanical stresses.
A Mathematical Model
Mathematically, ductility can be defined as the fracture strain, or the tensile strain along one axis that causes a fracture to occur. Fractures range from brittle fractures (Fig. 1) to fully ductile fractures (Fig. 2), resulting in very different physical appearances associated with the different types. This can be modeled on a stress/strain curve (https://www.nde-ed.org/EducationResources/CommunityCollege/Materials/Graphics/Mechanical/Brittle-Ductile.gif) showing where fracture occurs along the graph.
Quantitatively being able to measure ductility is important with regards to comparing ductility between different materials. Ductility can be measured through two main methods: percent elongation and percent reduction of area. The formulas can be found below: (http://www.engineersedge.com/material_science/ductility.htm)
Percent Elongation = (Final Gage Length - Initial Gage Length) / Initial Gage Length
= ((Lf - Lo) / Lo) * 100
Percent Reduction of Area = (Area of Original Cross Section - Minimum Final Area) / Area of Original Cross Section
= (Decrease in Area / Original Area)
Connectedness
As an engineering major, determining the correct material for components can be high risk. Knowing different materials ranges of ductility, can be integral in choosing the best option. This is especially important in materials that have a high applied tensile strength.
History
Percy Williams Bridgman's findings on tensile strength and material properties led to much of what is known about ductility, including that it is highly influenced by temperature and pressure. These findings led him to win the 1946 Nobel Prize in physics.
See also
Further reading
https://en.wikipedia.org/wiki/Ductility
External links
References
https://en.wikipedia.org/wiki/Ductility https://en.wikibooks.org/wiki/Advanced_Structural_Analysis/Part_I_-_Theory/Materials/Properties/Ductility https://en.wikipedia.org/wiki/Ductility#/media/File:Ductility.svg https://en.wikipedia.org/wiki/Percy_Williams_Bridgman http://www.engineersedge.com/material_science/ductility.htm
