Tensile strength refers to the amount of load or stress that a material can handle until it stretches and breaks. As its name implies, tensile strength is the material’s resistance to tension caused by mechanical loads applied to it.
Terms such as ultimate tensile strength (UTS) or ultimate strength are used interchangeably with tensile strength.
A particular material’s response to tension stress – that is, the force from an axial pull – depends on the nature of the said material. Some materials exhibit an abrupt fracture when the tensile capacity is reached. Others, meanwhile, show deformation or necking before completely breaking apart.
In alloys, tensile strength is influenced by composition, for example the amount of carbon in carbon steels.
How is it measured?
A tensile test measures the level of strength that a material possesses. A material testing laboratory usually conducts the test using a universal testing machine (UTM), which holds a specimen material in place and applies the tension stress needed to check the breaking point. The equipment is connected to an extensometer, which measures changes in the specimen’s length.
The specimen used for tensile testing is shaped into a round bar with a large shoulder on either end, from which the UTM can grip the material during application of tensile stress. As the machine pulls the specimen, change in the gage length is measured.
This same test can also determine yield strength, which measures the maximum amount of stress before showing plastic deformation.
The test is conducted in a controlled environment to prevent other factors from coming into play, such as temperature and exposure to impurities.
Tensile strength is measured in pressure units, most commonly in units of Pascal (MPa or GPa in stronger materials).
Strength-to-weight ratio is an important parameter for structural engineers and material manufacturers. This figure is calculated by dividing the load-carrying capacity by the material weight. When a particular material or structural component is expected to receive tension stress, the strength-to-weight ratio determines how much the material can withstand.
Tensile strength of materials
Each material has its own unique tensile capacity. This is the reason why some materials are effective for industries and applications where tension stress occurs.
Graphene is considered to be one of the strongest materials able to withstand tension stress. Its tensile strength is 130,000 MPa, which is higher than steel (at 400 - 2,700 MPa). As a result, the material may be manufactured as ultra-thin sheets that are extremely strong and durable. Because of its high capacity for tension stress, this carbon allotrope has found its way into buildings and aircraft design.
Boron nitride nanotubes have a tensile strength of 33,000 MPa, which makes it a suitable material for aerospace applications.
Plastics exhibit relatively low tolerance for tensile stress, with most of its variants experiencing elongation and tearing at only 5 MPa as in the case of PVC-P.
Here are other common materials and their tensile strength profiles:
- Carbon fibre = 7,000 MPa
- Aramid / Kevlar = 3,757 MPa
- Diamond = 2,800 MPa
- Mild steel = 840 MPa
- Brass = 500 MPa
- Human hair = 200 MPa
- HDPE = 37 MPa
- Glass = 33 MPa
Applications where tensile strength is important
Materials with high strength against tension stress are useful in the following applications:
- Manufacturing of metals: Most metals are designed to have high strength, and so developing metal materials and alloys requires careful consideration of the tensile strength.
- Aerospace applications: Due to the speed and pressure differences experienced by aircraft structures, manufacturing of these vessels require materials with high tensile strength.
- Bridges and suspensions: The forces exerted on bridges come from vehicle weight and wind force, and it’s imperative that the materials used in these structures can withstand extreme tension pressure.
- Ropes and cables: Based on their intended purposes, these paraphernalia require a high degree of durability against tensile stress. This is especially useful when they’re used in marine vessels, suspension bridges, and other similar applications where pulling is a necessary action.