Elongation at break is one of the most important mechanical parameters and indicates how much plastic deformation a material can withstand before failure. This property is of particular importance in materials science and industrial design because it is directly related to the elasticity and strength of the material. In this article, we analyze this property in detail, as well as its measurement methods and practical applications.
Determination of elongation at break
Elongation at break is the percentage increase in length of a material specimen compared to its original length at break under tension. This parameter is usually expressed as a percentage.
Calculation formula:
EB = [(Lf – L₀)/L₀] × 100 %
Where:
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EB: Elongation at break (%)
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Lf: Length of the specimen at failure (mm)
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L₀: Initial length of the sample (mm)
Important points:
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A measure of the deformability and elasticity of a material.
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This is directly related to the durability of the material.
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For brittle materials this value is very low, but for plastics it is high.
Extension type
1. Regular renewal
Change in length up to the beginning of the “neck”
2. Neck with subsequent extension
Change in length from the beginning of shrinkage to the breaking point.
3. Full extension
Overall uniform stretch after shrinking
Factors influencing elongation at break
1. Atomic structure and bond types
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Metallic binder : high elongation
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Covalently/ionically bonded materials: low elongation
2. Microstructure of the substance
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granules
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Current status
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Distribution of contaminants
3. Test conditions
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Loading speed
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Temperature test
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Sample size
4. Production process
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work hard
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Heat treatment
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Method of plastic surgery
Comparison of the elongation of different materials
Metal:
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Low-carbon steel: 20–40%
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Pure aluminum: 40-50%
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Copper: 45-60%
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Grey cast iron: <1%
Polymer:
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Polyethylene: 100–1000%
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Natural rubber: 500–700%
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Polycarbonate: 50-120%
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Epoxy resin: 1-6%
Composite materials:
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Carbon fiber/epoxy resin: 1–3%
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Kevlar fibers: 2–4%
Measurement method
1. Standard tensile test (ASTM E8 for metals)
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A strain gauge can be used to precisely measure changes in length.
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Final length if registration failed
2. Indirect method
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Relationship to other mechanical properties
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Using reference data
3. Different criteria
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ISO 527 for polymers
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ASTM D638 Plastics Standard
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DIN 50125 Metals
The importance of stretching in technology
1. Product design
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Prediction of material behavior under load
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Prevent sudden outages
2. Material selection
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Determine the acceptable distortion
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Meet functional requirements
3. Quality control
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Confirm the material specifications
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Detection of microstructural changes
4. Safety assessment
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Predicting the behavior of a substance under critical conditions
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Design with sufficient safety factors
Relationship to other mechanical properties
1. Limits of flexibility
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In general, materials with high yield strength have low elongation.
2. Flexibility
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Higher elongation generally indicates better strength.
3. Modulus of elasticity
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Materials with a high modulus of elasticity generally exhibit lower elongation.
4. Behavior when tired
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Strain influences fatigue life.
Industrial application
1. Automotive industry
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Material selection for safety components
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Design of energy-absorbing components
2. Packaging
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Highly elastic polymer materials
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Impact resistance and flexibility
3. Medicine
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Malleable implants
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Disposable consumables
4. Construction
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Steel rods with sufficient flexibility
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Sealing materials
Ways to improve stretching
1. Alloy
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Add suitable alloying elements.
2. Heat treatment
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Annealing to restore elasticity
3. Modification of the microstructure
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Granule control
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Sedimentary flood management
4. Use of composite materials
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A mixture of plastic and hard materials.
Limitations and problems
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This depends largely on the test conditions.
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The difficulty of interpreting anisotropic materials
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Behavioral differences at different levels
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Influence of environmental factors (temperature and humidity)
Relevant rules
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ASTM E8: Standard Test Method for Tensile Testing of Metals
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ISO 6892-1: Tensile test at room temperature
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ASTM D638: Tensile Testing of Plastics
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DIN 50125: Tensile test specimens for metals
Finally
Elongation at break, a measure of a material’s ductility, plays a crucial role in the development and selection of materials. A better understanding of this property and the factors that influence it enables engineers to more accurately predict material behavior and develop safer products. Despite the development of new materials, controlling and improving this property remains a key challenge in materials science.
Frequently Asked Questions
1. What is the difference between strain and plastic deformation?
Strain is a quantitative measure of deformation up to the point of failure, while plastic deformation refers to any permanent deformation.
2. Why do brittle materials have low elongation?
Because plastic deformation cannot occur before failure.
3. What influence does temperature have on the strain?
In general, the strain increases with increasing temperature (except for some special cases).
4. Is high elongation always desirable?
No, it depends on the application. In some cases, we need a material with less deformation.
5. How can the elongation of polymers be increased?
By adding plasticizers, changing the molecular structure or using copolymers.