Elongation at Break: What is It?

What Is Elongation at Break?

A material's elongation at break is a measure of how far it can stretch before breaking. Materials used in manufacturing or construction applications that require ductility and flexibility, it is a crucial mechanical property. Meeting a minimum value for elongation at break is frequently a customer requirement, and is often used as a quality assurance metric. Meeting ductility specifications help ensure that a lot of material can withstand the stresses it will experience in its intended application.

Elongation is calculated as the percent change in the length of a test specimen gauge section before and after a tensile test. This article will define elongation at break, describe a method for testing and calculating it, and provide a review of the ductility and elongation in the tension of a number of materials.

Elongation at break is important in assessing a material's capacity to plastically deform in a safe way, allowing designers and engineers to avoid brittle failure in their creations. It is critical in applications for materials like rubber and plastic where the material will be stretched repeatedly or subjected to impacts.

For instance, in the automotive sector, elongation is a hugely important parameter for assessing the reliability and dependability of vehicle components. The fatigue limit stress is a top priority in the component designs because it allows for controlled failure through plastic deformation prior to final failure. For these parts, a high tensile elongation value is typically preferred, because it denotes a high degree of ductility and flexibility. It helps prevent failure under difficult circumstances. Elongation at fracture is also crucial in making packaging materials like protective plastic packaging. To guarantee that the products they contain are safeguarded during shipping and handling, these materials must be able to stretch and flex without breaking. 

The Formula for Elongation at Break

The formula for elongation at break is:

Elongation at Break = (Final Length - Original Length) / Original Length x 100%

The steps below can be used to determine a material's elongation at fracture:

1. Measure the original length of the gauge section of a standard tensile test specimen.
2. Perform a tensile test according to a standard method.
3. Measure the final length of the gauge section at the end of the test, after the test specimen has fractured.
4. Subtract the original length from the final length to obtain the change in length.
5. Divide the change in length by the original length and multiply by 100% to obtain the total percent elongation.

Example: Using an aluminum sample, the following example illustrates how to determine elongation at the break:

1. Take measurements of the aluminum sample’s original length and diameter. Let’s say the original length is 50 mm.
2. To determine the length at which the aluminum sample breaks, apply tension to it until it snaps. Consider that the sample ruptures at a length of 75 mm.
3. Calculate the change in length of the sample:

Change in length = final length - original length

Change in length = 75 mm - 50 mm

Change in length = 25 mm    

Elongation at Break = (change in length / original length) x 100%

Elongation at Break = (25 mm / 50 mm) x 100%

Elongation at Break = 50%

Therefore, the elongation at break for the aluminum sample is 50%.

Here is a typical example of a stress-strain curve below:

Elongation at break is a unitless quantity that is normally expressed as a percentage. Elongation is expressed as a percentage because it describes the increase in the length of the material relative to its initial length at the point of failure in tension. The ductility or stretchability of various materials can be easily compared using this elongation metric.

Materials Often Tested for Elongation at Break

1. Steel

To ascertain the material properties necessary for design and quality control purposes, mechanical testing, including the tensile test (which is used to assess elongation at break), is required. To guarantee the safety and reliability of the finished product, adequate control of metal properties and expert joining techniques are essential. In general, the elongation at break of various steel alloys is in the 10-20% range.

2. Textiles

Natural fibers such as cotton, wool, and silk, as well as synthetic fibers such as polyester, nylon, and rayon, can all be used to create textiles. Each kind of fiber has particular characteristics that can have an impact on the elongation at fracture of the finished textile material. Cotton fibers typically have a breaking elongation between 4-8%. It is significantly less than that of wool fiber, which typically has a breaking elongation between 25% and 45%. Likewise, polyester fibers have an elongation rate that is significantly higher than cotton, at over 50%.

3. Metals

The results of elongation at break tests on metals can be affected by a number of variables, including temperature, composition, and cold work. The ductility and toughness of metals, as well as other mechanical characteristics, can be impacted by temperature changes. The metal’s composition, such as the existence of alloying elements, may also have an effect on its elongation at break values. Metals’ strength can be increased through cold work processes like rolling or forging, but this can also reduce the metals’ ductility and elongation at break values. The elongation at break of a typical aluminum alloy and pure copper is 17% and 60%, respectively.

4. Polymers

Both synthetic and natural polymer materials have long-chain molecules made up of repeating units. PVC, polystyrene, Teflon™, and polyethylene are some examples of polymers. When conducting elongation at break tests, the potentially large plastic deformation that occurs during stretching is typically handled by carefully controlling the test conditions, such as the rate of loading and the temperature. In addition, the test specimens are designed to have a specific shape and size, such as a dog-bone shape, to ensure consistent and repeatable results. The deformation and failure behavior of the material can also be characterized using techniques such as stress-strain curves and fracture mechanics analysis. However, in general, this property is determined by subjecting the material to a controlled amount of tensile stress until it reaches its breaking point. Rigid polyvinyl chloride (PVC) has an elongation at break of 25-58%, compared to polystyrene’s 1-70%, Teflon™’s 40-650%, and polyethylene’s 300-900%.

5. Rubber Materials

Rubber is well known for its capacity to stretch considerably before breaking. Some elastomers are more capable of stretching than others. Natural rubber, for instance, can elongate up to 700% before breaking at its maximum elongation. Fluoroelastomers, on the other hand, have a 300% elongation limit. The two primary types of rubber materials are natural rubber and synthetic rubber. Both types of rubber materials have their elongation at break tested because it is a crucial mechanical property that determines whether rubber materials are suitable for particular applications. Clamping a sample of rubber material at two points and then applying a tensile force until the sample breaks constitutes the test procedure.   

Key Factors Affecting Elongation at Break Values

1. Temperature. Higher temperatures cause greater elongation at break.
2. Testing Velocity. Higher values are achieved by allowing polymer relaxation during slow testing.
3. Filler Content of Composites. Composites' elongation at fracture tends to be reduced as filler content is increased.
4. Orientation of the Fibers. The elongation of break values of a material can be significantly influenced by the orientation of the fibers within it. As an illustration, materials with aligned fibers (like unidirectional composites) typically have a higher elongation at break values along the fiber direction and lower values in the transverse direction. On the other hand, in randomly oriented fibers, the elongation at break is more isotopic.

Common Testing Standards for Calculating Elongation at Break

For calculating elongation at break, several widely used testing standards are available, including:

1. ISO 527-1/2 - Plastics: Determination of Tensile Properties: Offers instructions for evaluating the tensile characteristics of plastics, including elongation at break.
2. ASTM D882 - Standard Test Method for the Tensile Properties of Thin Plastic Sheeting: The method for measuring the tensile characteristics of thin plastic sheeting, including elongation at break, is described in this standard.
3. ISO 37:2017 - Rubber, Vulcanized or Thermoplastic - Determination of Tensile Stress-Strain Properties: Provides instructions for evaluating the tensile characteristics of rubber and other elastomers, including elongation at break.
4. ASTM D638 - Standard Test Method for Tensile Properties of Plastics: Provides instructions for calculating the elongation at break and measuring the tensile strength of plastics and other resin materials. Additionally, it establishes accuracy standards for the tools and test frames that are used. 

How Elongation at Break is Used in 3D Printing

Engineers designing parts to be 3D printed take into account the elongation at break of the various candidate materials in order to select the best one for a given application. To create sturdy, printed objects that can withstand the stresses they will encounter in use, it is imperative to have a thorough understanding of a material’s ductility.

In FDM (Fused Deposition Modeling) 3D printing, elongation at break is affected by the orientation of the printed part. FDM prints are anisotropic, which means that they have various physical characteristics in various directions. FDM parts consequently have a different elongation at break values depending on the direction of pulling. For instance, a part pulled perpendicular to the print layers will have a different elongation at break than a part pulled parallel to the print layers. For more information, see our guide on 3D Printing.

Elongation at Break of Different 3D Printing Materials

The elongation at break values of various 3D printing materials can vary significantly depending on the particular material and its composition. For commonly used 3D printing materials, the following general ranges of elongation at break values are provided:

1. PLA (polylactic acid): 5-10%
2. ABS (acrylonitrile butadiene styrene): 5-50%
3. PETG (glycol-modified PET): 58-110%
4. TPU (thermoplastic polyurethane): 400-700%
5. Nylon: 5-120%

It is important to keep in mind that these values represent general ranges and may change based on the material's precise formulation and the printing environment.

Benefits of Calculating and Using Elongation at Break

1. Increased flexibility of the finished product
2. Greater design freedom
3. Enhanced durability and toughness
4. Reduced risk of breakage
5. Improved impact resistance

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1. Teflon™ is a registered trademark and a brand name (Teflon ®) owned by Chemours (formally DuPont)

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