What is the difference between tensile and elongation?

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Kelly.C

Marketing Manager--US & EU

Elongation refers to the ability of rubber to stretch before breaking

Elongation and tensile strength are key factors when evaluating rubber. But what sets them apart?

Elongation refers to the extent of stretching a material, while tensile strength measures its resistance to breaking under stress.

Let’s dive deeper into how elongation and tensile strength affect rubber performance and production.

What is the meaning of elongation in rubber?

Elongation refers to the ability of rubber to stretch before breaking. It’s a vital property for rubber used in various industries.

Elongation in rubber1 is the percentage increase in length under stress before breaking, a key indicator of rubber's flexibility.

When we talk about elongation in rubber, we're often discussing how much a material can stretch before it reaches its breaking point. This property is essential for determining the flexibility and durability of rubber products. Rubber with high elongation can stretch significantly, making it ideal for applications that require flexibility, like seals and gaskets.

However, too much elongation can also cause the rubber to lose its shape over time, particularly under constant stress. This is why manufacturers aim for a balance between elongation and tensile strength.

Elongation is typically measured as a percentage of the original length. For example, if a rubber sample stretches 100mm to 120mm, its elongation at break would be 20%. It gives us an idea of the material's overall "stretchability."

Rubber Type Elongation at Break (%) Common Use Cases
Natural Rubber 300-600 Automotive seals, gaskets
EPDM 150-400 HVAC, weather seals
Nitrile 200-350 Oil-resistant seals

What is elongation at break of rubber?

Elongation at break measures how much a rubber material stretches before it fails. It is crucial in testing rubber's elasticity.

Elongation at break2 is the percentage increase in length a rubber sample undergoes before it breaks, indicating its ductility.

Elongation at break is a key factor when evaluating rubber products. It is determined by stretching a rubber sample until it breaks and measuring the increase in length. This value is expressed as a percentage of the original length. For instance, if a rubber piece initially measures 100mm and breaks at 250mm, the elongation at break would be 150%.

Rubber that stretches more before breaking is considered more flexible, which is important for applications like seals, hoses, and weatherstripping. However, if the elongation at break is too high, the material may lack strength, which could lead to issues with durability and wear resistance. Therefore, manufacturers need to find the right balance.

Additionally, elongation at break can vary significantly between different types of rubber, as some materials are naturally more stretchable than others. For example, silicone rubber can stretch up to 500%, while natural rubber can stretch up to 600%.

Rubber Type Elongation at Break (%)
Silicone 300-500
Nitrile 150-400
Butyl 200-400

How to calculate elongation from tensile strength?

To calculate elongation, we need both the tensile strength and the initial length of the rubber sample.

Elongation can be calculated by measuring the original length and the final stretched length, one divides the change in length by the original length and then multiplies the result by 100..

Calculating elongation3 from tensile strength involves understanding the relationship between the two properties. The tensile strength is a measure of the maximum stress a rubber sample can withstand before breaking. To calculate elongation, Rubber elongation formula4 is:

the formula calculate elongation from tensile strength

This formula gives us the percentage increase in length, which helps in evaluating the flexibility and stretchability of the rubber. It's important to note that while tensile strength and elongation are related, they are not the same. Tensile strength measures the maximum force the rubber can handle, while elongation measures how far it can stretch before failure.

Measurement Value
Original Length (mm) 100
Final Length (mm) 150
Elongation at Break (%) 50%

What is the ASTM test for elongation?

The ASTM test for elongation is a standard method for measuring the elongation properties of rubber materials.

The ASTM test for rubber elongation is defined by ASTM D412, which evaluates the tensile properties of vulcanized thermoset rubbers and thermoplastic elastomers.

This standard includes two primary methods: Method A, which utilizes dumbbell-shaped specimens, and Method B, which employs cut ring specimens.

The ASTM (American Society for Testing and Materials) provides specific standards for measuring elongation in rubber materials. ASTM D412 test5 is one of the most widely used methods for testing rubber elongation. In this test, a rubber sample is placed in a tensile testing machine, and the force required to stretch the material is applied until the sample breaks. The elongation at break is then calculated as the percentage increase in length.

ASTM testing procedures ensure consistency and reliability, allowing manufacturers to compare different rubber materials and select the most appropriate for their applications. This test is important for industries like automotive, construction, and HVAC, where rubber's ability to stretch and return to its original form under stress is critical.

The ASTM test also includes guidelines for sample preparation, testing speeds, and environmental conditions to ensure accurate and repeatable results. These standardized tests help in determining the material's suitability for specific uses, based on its elongation properties.

Test Standard ASTM D412
Test Type Tensile test
Sample Size 50mm x 10mm strip
Speed 500 mm/min
Elongation Percentage increase

Key Aspects of ASTM D412

  • Purpose: The test measures the material's ability to withstand tensile forces and determines properties like tensile strength, ultimate elongation (the maximum elongation before rupture), and tensile set (the permanent deformation after the load is removed).

  • Procedure:

    1. Prepare a sample in a "dogbone" shape or as specified for the method being used.
    2. Load the sample into a universal testing machine equipped with suitable grips for elastomers.
    3. The sample is then elongated at a specified rate (typically around 500 mm/min) until it fractures.
  • Measurements: The test provides quantitative data on elongation, stress at specific elongations, and other tensile characteristics. It is essential for assessing the performance of rubber materials in various applications.

This standardized testing method ensures that results are consistent and comparable across different materials and testing conditions, making it crucial for quality control in rubber manufacturing.

Difference Between Tensile and Elongation

Tensile

  • Tensile strength indicates how much force a material can handle before it breaks. It is a crucial parameter for assessing the durability and performance of materials under tension.

Elongation

  • Elongation provides insight into a material's ductility, indicating how much it can deform plastically before failure. Higher elongation percentages suggest that a material is more ductile and can absorb more energy before breaking.

Summary of Differences

Aspect Tensile Elongation
Definition Maximum stress before fracture Percentage increase in length before fracture
Measurement Measured in psi or MPa Expressed as a percentage
Focus Resistance to pulling forces Ability to stretch and deform
Significance Indicates material strength Indicates material ductility

Conclusion

While tensile strength measures how much force a material can withstand, elongation measures how much it can stretch before breaking. Both properties are essential for understanding the mechanical behavior of materials under load.

Footnotes:


  1. For more detailed explanations of elongation in rubber. 

  2. learn more about elongation at break and its significance in rubber properties. 

  3. An in-depth explanation of tensile strength and how to calculate elongation. 

  4. further explore the formula for rubber elongation and its applications. 

  5. understand the ASTM D412 test in greater detail. 

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