Elongation at Break: Definition, Calculation, Benefits, Limitations, and Examples
Learn more about what this measurement is and how it works in terms of a material's ductility and toughness, specifically in engineering and manufacturing applications.
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 a measure of a material’s ductility and toughness. It quantifies the amount of deformation a material can withstand before breaking. Elongation is a metric that is regularly employed in the testing and assessment of materials for engineering and manufacturing applications.
Elongation at break works in many materials such as metals. The primary mechanism of plastic deformation in metals is slip movement. It takes place when the applied stress exceeds the critically resolved shear stress and causes atoms to slide over one another within the crystal lattice. Dislocations move along tightly packed planes and directions known as slip systems to cause this process. On the other hand, twinning takes over as the primary mechanism of plastic deformation in situations where slip is not an option.
In twinning, local atoms rearrange as mirror images of one another across a twinning plane as a result of an orientational change in the atoms. Twin planes and twin directions are defined planes and directions in crystallography where twinning occurs. Twinning is advantageous when there are fewer slip systems present because it enables planes to develop more slip. Accordingly, depending on the structure and available slip systems, twinning as well as slip both contribute to plastic deformation in metals.
Elongation at break is important in assessing a material's capacity to plastically deform in a safe way, avoiding brittle failure. 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 freak 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:
- Measure the original length of the gauge section of a standard tensile test specimen.
- Perform a tensile test according to a standard method.
- Measure the final length of the gauge section at the end of the test, after the test specimen has fractured.
- Subtract the original length from the final length to obtain the change in length.
- 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:
- Take measurements of the aluminum sample’s original length and diameter. Let’s say the original length is 50 mm.
- 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.
- 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 tensile stress-strain curves below:
Stress-Strain Curves of various metals.
Image Credit: Shutterstock.com/petrroudny43
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.
Elongation is measured as part of the data collected during a tensile test. Tensile tests are conducted on universal testing machines (UTS). The tests are conducted using standard test methods such as ASTM E8. A test specimen of one of several standard sizes and shapes is made of the material to be tested. An extensometer is attached to the test sample to acquire the length change data. The test continues until the sample breaks, with the UTS continuously recording the strain reading from the extensometer as increasing tensile stress is applied by the machine.
The following are some of the materials typically tested for elongation at break:
To ascertain the material properties necessary for design and quality control purposes, mechanical testing, including the tensile test, 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.
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%.
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. For more information, see our guide on Metal.
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%.
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.
The following variables can affect a material's elongation at break values:
- Temperature. Higher temperatures cause greater elongation at break.
- Testing Velocity. Higher values are achieved by allowing polymer relaxation during slow testing.
- Filler Content of Composites. Composites' elongation at fracture tends to be reduced as filler content is increased.
- 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.
A material's elongation at break can be significantly influenced by its chemical makeup. For example, the presence of stiffening fillers or crosslinking agents can reduce the elongation at break of thermoplastics. The presence of plasticizers or softening agents can increase a material’s flexibility.
For calculating elongation at break, several widely used testing standards are available, including:
- ISO 527-1/2 - Plastics: Determination of Tensile Properties: Offers instructions for evaluating the tensile characteristics of plastics, including elongation at break.
- 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.
- 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.
- 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.
Tensile strength evaluates a material's capacity to withstand stretching forces before breaking, whereas elongation at break evaluates a material's ability to plastically deform before fracturing. Materials with a lower tensile strength typically have a higher elongation at break values.
Although both yield strength and elongation at break are mechanical properties of a material, they measure different things. The yield strength of a material is the stress at which it begins to deform plastically under tension, whereas the elongation at break indicates how much total deformation occurs before the material breaks. High-yield strength materials typically have a low elongation at break, and vice versa. This is due to the fact that materials with high-yield strengths typically have fewer atomically mobile dislocations and/or fewer slip systems for dislocations to move on. Dislocation pinning usually results in a rise in strength and a fall in ductility. On the other hand, materials with low yield strengths are usually more ductile and can withstand more deformation before breaking.
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 can optimize 3D product design in the following ways:
- It enables more design flexibility and the production of intricate geometrics without compromising structural integrity.
- It helps the material to withstand impact better. This is a result of enhanced ductility.
- Designers can reduce component thickness while maintaining structural integrity by utilizing more ductile materials. As a result, there is less material waste and weight, which can save money.
- When used in manufacturing processes like forging and rolling, materials with high ductility are simpler to form and shape. This can increase production efficiency, lower costs, and improve the quality of the finished product.
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:
- PLA (polylactic acid): 5-10%
- ABS (acrylonitrile butadiene styrene): 5-50%
- PETG (glycol-modified PET): 58-110%
- TPU (thermoplastic polyurethane): 400-700%
- 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.
Yes, elongation at break is important to consider when selecting 3D printing materials because it shows how flexible the material is before it breaks. This is crucial for parts that might be stressed or impacted during use. The strength and longevity of the printed part can be guaranteed by selecting a material with the proper elongation at break.
The benefits of measuring and taking into account elongation at break include:
- Increased flexibility of the finished product
- Greater design freedom
- Enhanced durability and toughness
- Reduced risk of breakage
- Improved impact resistance
The limitations of depending on elongation at break for engineering design guidance are listed below:
- It may not provide a complete picture of a material's mechanical properties
- It may not accurately reflect a material's ability to withstand stress over time
- Environmental factors, such as temperature and humidity, can significantly impact test results
- It only measures the ability of a material to stretch before breaking, not its overall strength or durability
- Can vary depending on the sample size and testing conditions used
Yes, elongation at break shows the amount of deformation a material can withstand before failing. This is because the material's elongation at break, or ductility, is a measure of its capacity to withstand plastic deformation without breaking. A material that can plastically deform more before breaking is more ductile and has a higher elongation at break value.
Yes, materials with higher elongation at break values are typically less likely to break catastrophically. This is because they have a greater capacity for plastic deformation without fracture. This reduces the possibility of abrupt and total failure because these materials can stretch more before breaking when put under stress or strain. However, other factors, such as material strength and environmental circumstances, can also have an impact on how a material fractures.
This article presented elongation at break, explained what it is, and discussed how to calculate it and its benefits. To learn more about elongation at break, contact a Xometry representative.
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