Examples of Ductile Materials

Sarah
DeGuzman

Ductile materials break with lots of elongation before failure. In this article, you will receive examples of ductile materials, learn about fracture type, and determine how to reduce the material ductility.

Examples of Ductile Materials

Metals and polymers are examples of materials that are often categorized as ductile. Elongation provides a standard measurement of ductility. Materials with 5% or more excellent extension before fracture are generally consider ductile.

Metals

A metal is a material that has a glossy appearance when freshly produced, polished, or shattered and conducts electricity and heat reasonably well. 

Metals are typically ductile. Because they are made up of layers of ions that can slide over one another when the metal is bent, hammered, or pressed, they have this property. This ductility allows for the drawing or pulling of metals into wires, making them excellent for electric cables. This is due to the ions sliding over each other.

Ductility refers to a metal’s capacity to withstand permanent deformation without fracture. Ductile metals can be manipulated or formed into different shapes. At extreme temperatures, all metals become ductile.

Metals have a high tensile strength, allowing for stretching without breaking. Tungsten, for example, has high tensile strength. Among commonly used metal alloys, stainless steel and tempered structural aluminum have relatively high tensile strengths: 90,000 and 45,000 PSI, respectively.  

The point where steel stops behaving elastically (i.e., return to its original stress) is essentially the yield point. The yield starts for most steels at approximately 0.2% elongation.

Polymers

A polymer is a macromolecular substance consisting of many repeating units connected by covalent chemical interactions. The monomers that were used to produce the polymer are represented by these repeating units. As a result, the monomers undergo polymerization to form a polymer. 

Natural and synthetic polymers are the two most common types of polymers. Biopolymers like protein and nucleic acids are natural polymers, whereas synthetic polymers include man-made polymer materials like plastic and nylon.

Actual photo of polymers
Courtesy: Ìtàn

Polymers are present in almost all aspects of modern life. Grocery bags, soda and water bottles, textile fibers, phones, laptops, food packaging, automotive parts, and toys contain polymers.

It’s important to remember that the ductile/brittle transition temperature observed during polymer cooling may not necessarily equate to the brittle/ductile transition temperature observed during polymer heating. At the lowest temperature, polymers are brittle. As the temperature increases, they become tougher until they reach Ductile-Brittle Transition Temperature.

PAI – Polyamide-imide (PAI) boasts the highest tensile strength of any plastic at 21,000 psi.

Fracture Type

Depending on the plasticity of the material, fractures are classified as ductile or brittle. The degree of plastic deformation that a material can bear also influences the type of fracture changes. 

It’s difficult to tell the difference between brittle and ductile fractures, though. This is because several factors influence material deformation. The stress rate, speed of loading, ambient temperature, and the material’s crystal structure are all factors to consider.

Ductile failure of a specimen strained axially
Courtesy: Wikipedia

If the only deformation occurs at the micro-level, the fracture refers to as a brittle fracture. Plastic deformation indicates the onset of a fracture. 

In contrast, plastic deformation of the material at the crack tip occurs in a ductile fracture. This frequently leads to a steady and predictable fracture mode in which crack growth occurs only when the applied force increases; as the load decreases, the crack stops expanding. As a result, the ductile fracture is the preferred failure mode for damage-tolerant materials.

Reducing Unwanted Ductile Fracture

If a purely ductile failure does occur, it is usually because of an error in design or because, in practice, the actual loading is higher than anticipated (such as excessively high wind loading during a hurricane or load redistribution after the failure of another member in the structure).

A copper rod fracture is an example of ductile fracture. Tensile fractures occur with a lot of plastic deformation and absorb a lot of energy prior to fracture.

If you apply a force to a copper rod that contains a small notch, the rod plastically deforms, and the gap does not decrease the energy required to break the rod.

To prevent ductile fracture, the material must have refined grains, a high hardness value, and must not show any defects or dislocations. Additionally, it is preferred that the material has high Young’s modulus and cohesive energy.

By understanding ductile failure, engineers can develop more dependable and safer industrial products and materials.