Expansion of the outdoor area

Surface strain is one of the most important mechanical properties in materials science and engineering . It measures the extent of plastic deformation a material undergoes when subjected to a force. It plays a fundamental role in analyzing the mechanical behavior of metals, polymers, and even construction materials.

In a tensile test , the deformation of a specimen initially remains in the elastic range. After the load is removed, the specimen returns to its original state. However, as the load increases, the specimen enters the plastic range and fractures, reaching a length greater than its original length. This increase in specimen length relative to the original length is called elongation.

Determination of strain

The formula for calculating the elongation is as follows:

$% elongation = Lf - L0L0^{\times} 100 % {^{L0}} multiplied by 100 % elongation = L0 Lf - L0 \times^{100}$

$L_0$ Initial length of the sample before applying the load
$L_f$ final length of the specimen after failure

This index characterizes the hardness and elasticity of a material . The greater the elongation, the higher the elasticity, and vice versa.

The importance of strain in materials science

Ductility : This value indicates how much a material can be deformed before it breaks.
Material selection in design : In the automotive, aerospace or construction industries, selecting materials with the correct elongation is critical to prevent catastrophic failures.
Quality Control : Elongation is one of the standard parameters used in tensile testing to determine the quality of raw materials.
Comparison of different materials : This index allows you to easily compare soft metals such as aluminum and hard metals such as steel.

Factors that influence stretching

There are several factors that influence stretching:

1. Woman

Soft metals such as copper and aluminum generally have higher elongation.
Hard, brittle metals such as cast iron or hard metal have less elongation.

2. Temperature

An increase in temperature normally leads to an increase in ductility and thus in elongation.

3. Heat treatment

Processes such as annealing can increase the ductility of the material.

4. Microstructure

The grain size and the presence of impurities in the structure of the material play an important role in the degree of deformation .

5. Test conditions

Download speed
Primary sample length
Variation cross-section

They all influence the final result.

Macartney – Advanced testing system for hydrostatic pressure vessels

Elongation of various metals

Mild steel: approx. 25–35%
Aluminum: 20% to 40%
Copper: 40% to 60%
Cast iron: less than 5%

These values show that copper and aluminum are more ductile than steel, whereas cast iron has very low elongation due to its brittle structure.

Application of stretching in industry

Automotive industry : Select sheets that must undergo large changes in length during pressing and forming.
Construction : Steel bars must have sufficient tensile strength to withstand earthquakes and sudden loads.
Aerospace : To prevent catastrophic failures, high-elongation alloys are used.
Wire and cable manufacturing : Copper and aluminum are widely used in the electrical industry due to their high elongation.

Relationship between elongation and other properties

Tensile strength: In general, elongation decreases with increasing tensile strength.
Strength: Materials with high elongation are generally stiffer.
Hardness: Higher hardness generally results in lower ductility and therefore lower elongation.

Tensile test standard

There are several criteria to accurately measure this indicator , including:

ASTM E8/E8M – Standard for Tensile Tests on Metals
ISO 6892 – International Standard for Tensile Tests
DIN 50125 – German standard for tensile specimens

These standards specify methods for specimen preparation, loading rates and the procedure for calculating strain.

Numerical example for calculating the strain

Let us assume that a steel specimen of initial length $L_0 = 50 mm$ is stretched $by a tensile test to a length$ $Lf$ $L_f = 62.5 mm$ $L$ $_{f}$ $=$ $62.5 mm .$

$% strain = 62.5 - 50 50 \times 100 = 25% 50 \times 100 = 25 % % strain = 62.5 - 50 \times 100 = 25 %$

The results show that the material can change its length by 25% before it breaks .

Advantages and limitations of using extensions

Benefits

Simple calculation
Ability to quickly compare materials
Important criteria for material selection in construction

End

This depends on the original length of the sample.
It only shows changes in longitudinal length and ignores changes in cross-sectional area or volume.
For brittle materials whose length does not change significantly before failure, this method may not provide sufficient information.

Finally

Elongation is one of the most important mechanical properties that describes the behavior of a material under load. This property, which characterizes ductility and resistance to sudden failure , plays a crucial role in material selection in many industries.

By properly understanding this concept, engineers can make more informed decisions when designing structures, industrial components, and various products, thereby improving the safety and efficiency of systems.