Tensile Strength: Definition, Importance, Types, and Examples

For manufacturers, tensile strength is one of the first things needed when it comes to choosing a suitable material for their products. In this article, we’ll cover exactly what it is, how it differs from other similar specs, and how to calculate it.

What is Tensile Strength?

The tensile strength of a material is how much load or pulling force it can take across a specific area before it either permanently stretches or breaks. While its yield strength is the point just before the material starts to stretch in a way that it can’t go back to its original shape, the tensile strength is the point at which it breaks. A material like steel has a high tensile strength, but a rubber band will be right at the bottom of the scale. 

For materials that stretch in a predictable way—like a spring, for instance—the response to the force applied, its “elasticity,” will depend on its “linear elastic zone.” If the force is within this zone, the spring will return to its original shape once the force is gone. If not, the material will break or be damaged beyond repair. You can see how tensile force differs from other types in terms of its direction in the below diagram.

What Is the Importance of Performing a Tensile Strength Test?

Tensile tests are used to learn about the strength properties of new material formulations. It is used to check the results of heat treatments of other processes, or to verify that a lot of material meets its original specifications. Validation of the properties of incoming raw materials is a critical part of process control and failure prevention. This is whether a supplier does the testing and the customer accepts it, or whether the customer chooses to check the supplier's claims about a lot of material.

At the part fabricator's plant, testing the tensile strength of materials can be a process control step. It helps ensure that materials are in the correct condition with regard to heat treatment, case hardening, curing, or any other manufacturing step that changes the material's strength and ductility. In a research and development setting, tensile testing is an easy way to check whether a proposed formulation has the characteristics sought for a new application, or for improvement of an existing one.

Tensile tests can be performed on test bars that are cast to shape or machined from raw material. They can also be machined from an actual cast or machined component if there is a critical need to check properties in one section of a large part.

What Is the Importance of Tensile Strength in 3D-Printed Parts?

Tensile strength is an important factor in 3D printing, specifically due to the potential for directional tensile properties. For example, 3D-printed plastic parts using FDM (fused deposition modeling) technology will have a lower tensile strength along their z-axis, where the z-axis refers to the vertical height of the part. This is because the individual layers are not completely fused to each other and are only in contact with each other over a small surface area.

Many material data sheets for 3D-printed materials will indicate the tensile strengths in different directions within the material (commonly in the Z and XY directions). Other 3D printing technologies, such as SLM  (selective laser melting), will produce parts with an isotropic structure, which means their properties are equal in all directions.

What Is the Ideal Tensile Strength for 3D Printing Materials?

The ideal tensile strength depends on the application of the part, the material being used, and the magnitude and direction of loads being applied. For example, if a part is only loaded in compression, then tensile strength does not matter. Or if the part is an enclosure for electronics, then tensile strength is less important than anti-static and moisture absorption properties. When designing 3D-printed parts, the material is selected based on the application and not the other way around. 

Is It Important To Determine the Tensile Strength of 3D-Printed Materials?

Yes, it is important to determine the tensile strength of 3D-printed materials. But, only if the 3D-printed part will be exposed to mechanical loading. For example, if designing a 3D-printed ABS part, then it would be a mistake to use normal ABS properties. 3D printing material may have lower tensile strength compared to the material's theoretical tensile strength based on the 3D printing technology used.

How To Calculate the Tensile Strength of a Material?

To correctly measure tensile strength, we divide the force per unit of a cross-sectional area of the material instead of its whole surface. But you won’t be able to calculate a material’s tensile strength directly without first knowing its stress-strain curve. Don’t worry, we’ve got an article that tells you exactly how to figure this out. You’ll then perform the below equation:

σ = F/A – eq 1

• σ = stress
• F = force
• A = area

The SI tensile strength unit is MPa (N/mm2). Basically, the strength equals the stress at the point of failure of the material, and this failure point can be characterized by the force per unit area.

What Are the Different Types of Tensile Strength?

There are a few different types of tensile strength, but the term can mean whatever is most useful to you. For example, figures worked out under standard conditions will be the most useful to engineers who want to compare material formulations or lots, or those who are trying to figure out whether a material will be good for a particular task. The most common types used are yield strength, ultimate tensile strength, and breaking strength, and we’ll look at these in a little more detail below.

1. Yield Strength

As mentioned a little earlier, yield strength is the point at which permanent (or plastic) deformation begins in a material. For steel, this is once it’s been deformed past its proportional limit, usually seen as a straight line on a stress-strain curve. For material without a distinct yield point, like aluminum, yield strength is reported as the stress that coincides with 0.2% strain. In most cases, metal parts are designed to keep stresses in the service environment below the yield strength. In the case of very brittle materials, like ceramics, these will fail at very small deformations and do not yield at all. Other materials, like elastomers, can be stretched many times their original length without breaking and only show a small amount of permanent deformation once the load has been removed.

2. Breaking Strength

Also known as fracture strength, this refers to the point at which the material can no longer carry any more load and breaks. This can be seen as the end point of a stress-strain curve, i.e. point “ε” in the yield strength diagram above. The breaking point is also the point used for measuring total elongation.

3. Ultimate Strength

This is the maximum stress a material can handle before it ends up breaking under a tensile load. Some metals will experience strain hardening after passing their yield point, and they’ll continue to deform as the stress increases until they get to the material’s ultimate tensile strength. Not all materials, for instance plastics, will have a well-defined ultimate tensile strength.

What Are the Advantages and Disadvantages of Tensile Strength?

Tensile strength is a material property and does not have an advantage or disadvantage.

What Are the Examples of Tensile Strength for Different Materials?

Each class of material has a different behavior when under a tensile load. Ductile materials like low-carbon steel will plastically deform before failure, but more brittle materials, like high-carbon steel, will have very little deformation before failure. We’ve put some common materials in the table below along with their tensile strengths.

What Material Has the Highest Tensile Strength?

The material that has the highest tensile strength is graphene. Graphene has an ultimate tensile strength of approximately 130 GPa, making it stronger than carbon nanotubes, which until recently had the highest tensile strength. These materials are far stronger than the strongest elemental metal, tungsten, which has an ultimate tensile strength of 0.98 GPa, or the slightly stronger heat-treated Inconel®,  with an ultimate tensile strength of 1.034 GPa. It must be noted, however, that neither graphene nor carbon nanotubes can be cheaply mass-produced. 

What Material Has the Lowest Tensile Strength?

Plastics tend to have very low tensile strengths compared to metals and ceramics. For example, LDPE (low-density polyethylene) has a tensile strength of 10 MPa. Defining the material with the lowest tensile strength is difficult, as low-tensile strength materials have limited practical application, specifically for load-bearing uses. The listing of materials based on low tensile strength is not common practice. 

What Device Is Used To Measure Tensile Strength?

A tensile tester is used to measure the tensile strength of a specimen. This machine grips the test piece at each end and applies a controlled amount of tensile force to it, at a constant rate.  The machine automatically logs data on the load applied and the displacement of the grips for further analysis.

What Are the Applications of Tensile Strength?

Tensile strength is a material property and does not have an application.

What Are the Factors That Can Affect the Tensile Strength of a Material?

Tensile strength can be affected by various factors, such as.

1. Temperature: A material’s tensile strength usually goes down when its temperature rises. Below room temperature, most materials become slightly stronger, but they’ll also get less ductile.
2. Work hardening: The process’s whole concept is to plastically deform a material to make it harder. By rolling, hammering, bending, or stretching a metal, its crystal structure goes through microscopic changes that increase the yield and ultimate tensile strength, while at the same time reducing its ductility.
3. Additives: Glass or carbon fiber added to a material can increase the tensile strength of nonmetals, like nylon, for example.
4. Heat treatment: Like work-hardening, this also changes a metal’s microstructure and, depending on the type of treatment, could result in either an increase OR a decrease in tensile strength.
5. Defects: Surface and internal defects can reduce the tensile strength of a material as they create weak points where cracks are able to start.

What Are The Two Types of Tensile Strength Failure?

There are two main types of tensile strength failure: brittle and ductile.

1. Brittle Failure

Brittle failure occurs mainly with hard materials, like cast iron. The material will not deform much before it suddenly fails.

2. Ductile Failure

Ductile failure is the primary tensile failure mode for many structural steels and softer materials, like aluminum, and is gradual instead of instantaneous. After the material starts to yield, plastic deformation continues, then localizes, producing a "neck" that will be the site of the material’s final separation.

FAQs About Tensile Strength

In this section, our experts answer some of the most common questions we get in relation to tensile strength.

Copyright and Trademark Notices

1. Inconel® is a registered trademark of Special Metals Corporation.

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