Elongation at break

Elongation at Break is the ratio of the initial and final lengths of the plastic material before it breaks. This process takes place at a controlled temperature. 

It is the ability of plastic material to resist changes in shape without cracking. It is also known as fracture strain or tensile elongation at break. 

 

The elongation is calculated as the relative increase in length. 
 

where: 
 

• ɛ is the elongation
• ΔL is the final length
• L is the initial length

Elongation at Break is measured in % (% of elongation vs. initial size when break occurs). The maximum elongation at the break (Emax) is also called 'strain to failure'. 

 

Elongation at Break is an important mechanical property of materials. 
 

• It measures how much bending and shaping a material can withstand without breaking.
• It defines the ductility of a polymer.
• Used in components that absorb energy by plastic deformation.
• Used to screen materials for use as plastic hinges. High elongation at break is important for plastic hinges.

Ultimate elongation values of several 100% are common for elastomers and film/packaging polyolefins. Rigid plastics, especially fiber-reinforced ones, often exhibit values under 5%. Fibers have a low elongation-to-break, and elastomers have a high elongation at break. 

The combination of high ultimate tensile strength and high elongation leads to materials of high toughness. 

Materials that show high elongation are:
 

1. Thermoplastics with High Elongation – View Products
2. TPEs/TPVs with High Elongation – View Products
3. Rubbers with High Elongation – View Products
4. Thermosets with High Elongation – View Products

• Velocity of Testing: Slow testing allows for polymer relaxation and higher elongation at break values.

• Orientation Level: Fibers that are less oriented tend to exhibit greater degrees of elongation at break.

• Temperature: In general, the elongation at break increases with an increase in temperature.

• Filler Content: The elongation at the break of composites decreases with an increase in the filler content.

Tensile tests measure the force required to break a specimen. It also determines the extent to which the specimen stretches or elongates to that breaking point.

In general, 'tensile test methods' measure the modulus of elasticity of materials. The common methods used are
 

• ASTM D638 - Standard Test Method for Tensile Properties of Plastics
• ISO 527-1:2012 - Determination of tensile properties. General principles

These methods determine the tensile properties of plastics and plastic composites. This is done under defined conditions that can range from:
 

• pretreatment,
• temperature,
• humidity, and
• machine speed

The test specimens are in the form of a standard dumbbell shaped. 

For ASTM D638, the test speed is determined by the material specification. For ISO 527, the test speed is typically 5 or 50 mm/min for measuring strength and elongation, and 1 mm/min for measuring modulus. 

Apart from Elongation at Break, the tensile test results can also calculate:
 

• Tensile strength at yield
• Tensile strength at break
• Young's modulus
• Tensile modulus
• Strain
• Elongation and percent elongation at yield

An extensometer determines the elongation and tensile modulus. It is a device that measures the changes in the length of an object. It evaluates the stress-strain curve values.

The two main types of extensometers are contact and non-contact.
 

1. Contact extensometers are further divided into two types:
    

   • Clip-on extensometer: They can measure displacements from very small to relatively large. That is from less than 1 mm to over 100 mm. Used for applications requiring high-precision strain measurement (most ASTM-based tests). Major advantages include:
      
     • Low cost
     • Easy to use

    

   • Automated testing clip-ons: They replace digital "sensor arm" extensometers. They can be applied to the specimen automatically by a motorized system. They produce much more repeatable results than traditional clip-on devices. They measure very high extensions (up to 1000 mm) without losing any accuracy. Major advantages include:
      
     • Better linearity,
     • reduced signal noise, and
     • synchronization with the corresponding force data.
        
2. Non-contact extensometers: These devices are beginning to bring advantages for certain applications. Especially, in industries where it is impractical to use contact extensometers.

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