Tensile Testing Machines According to UNI EN ISO 6892

UNI EN ISO 6892

Tensile tests on metals are essential for evaluating the mechanical properties of metallic materials. The Tensile tests on metals are essential for evaluating the mechanical properties of metallic materials. The UNI EN ISO 6892-1 standardizes these tests, making the results  internationally comparable and ensuring that the materials used in various sectors meet quality and safety standards. But why is it so important? And how are these tests performed?

Purpose and Applications of UNI EN ISO 6892-1

The main objective of tensile tests is to determine the strength and deformation values of metallic materials. These values are fundamental in the design and construction of components, machinery, vehicles, and buildings. With tensile tests, we can ensure that the materials used are suitable for their specific applications.

Overview of the UNI EN ISO 6892 Standard

The UNI EN ISO 6892 standard is divided into four main parts, each relating to different temperature conditions under which the tests are performed:

UNI EN ISO 6892-1: Room temperature tests

This part of the standard covers tests conducted at room temperature, the most common context for most industrial applications.

UNI EN ISO 6892-2: High temperature tests

High-temperature tests are crucial for materials used in extreme environments, such as engines or turbines.

UNI EN ISO 6892-3: Low temperature tests

These tests are crucial for materials that must withstand extreme cold conditions, such as in aerospace applications or the cryogenic industry.

UNI EN ISO 6892-4: Tests in liquid helium

Liquid helium is used to achieve ultra-low temperatures necessary for certain advanced materials.

Key Values According to UNI EN ISO 6892-1

In tensile tests according to the UNI EN ISO 6892-1 standard, several characteristic values are determined. Here are the main ones:

Upper and lower yield points (ReH and ReL)

The yield point is where a material begins to deform plastically. The upper (ReH) and lower (ReL) points indicate the limits of this behavior.

Offset yield strength (Rp0.2)

The offset yield strength, generally determined as a substitute for the yield point at 0.2% plastic strain, is a crucial parameter for materials that do not show a clear yield point.

Elongation at yield point (Ae)

This value can be determined using an extensometer and indicates how much a material elongates before yielding.

Tensile strength (Rm)

The tensile strength represents the maximum load a material can withstand before breaking.

Non proportional elongation at maximum force(Ag)

This value measures how much a material can elongate uniformly before starting to neck or break.

Elongation at fracture (A)

The elongation at fracture is a measure of a material’s ductility and its flow properties.

Tensile Strength with Different Levels of Work Hardening of the Material

Metallic materials can present different levels of work hardening. The stress/strain curve varies based on these levels:

  • High level of work hardening: The maximum tensile force is reached after the upper yield point.
  • Low level of work hardening: The maximum tensile force may be lower than the upper yield point.

Bend Testing on Metals According to UNI EN ISO 6892-1

The UNI EN ISO 6892-1 standard also covers bend testing, which includes:

Yield point and yield load

To determine the yield point and yield load, precise measurement of the applied force is necessary.

Tensile strength

For tensile strength, precision in force measurement is fundamental.

Determination of elongation at fracture

Elongation at fracture is determined using modern algorithms that automatically analyze the stress-strain curve. It is important to consider the fracture location along the specimen to obtain an accurate measurement.

Use of Optical Extensometers

Optical, non-contact extensometers offer significant advantages over traditional contact extensometers:

  • Reliability: They can determine deformation along the entire parallel section of the specimen.
  • Accuracy: They provide accurate measurements even if the fracture occurs outside the initial gauge length.

Testing Requirements According to UNI EN ISO 6892-1

To obtain reliable results, the measurement of force and elongation must be precise. The test speed is equally important and is specified in the standard through two main methods:

  • Method A: Strain rate control.
  • Method B: Stress rate control.

Requirements for measuring Force and Elongation

UNI EN ISO 6892 refers to other standards for force and elongation measurement:

  • UNI EN ISO 7500-1: Calibration and verification of the force measurement system.
  • UNI EN ISO 9513: Calibration of extensometers used in uniaxial tests.

Influence of Test Speed on Yield Points

Test speed significantly influences the results. The standard distinguishes between:

  • Method A: Strain rate control.
  • Method B: Stress rate control.

Strain Control Methods According to UNI EN ISO 6892-1

To improve result reliability, the standard proposes two methods for strain control:

Method A1: Closed loop strain control

This method uses the extensometer signal for automatic and precise speed control.

Method A2: Open loop strain control

Manual adjustment of the crosshead speed is necessary to achieve the correct strain rate.

Method B: Stress rate control

This method does not require the use of an extensometer but is less precise than strain control methods.

Test Instruments for Strain Control

Cermac designs and manufactures testing machines according to UNI EN ISO 6892 standard.

Discover the machine catalog.

Conclusion

Standardized tensile tests according to the UNI EN ISO 6892-1 standard are essential for ensuring the quality and safety of metallic materials used in various sectors. Precise measurement of force and elongation, combined with rigorous control of test speed, ensures that the characteristic values obtained are reliable and reproducible.

FAQs

What is the main purpose of the UNI EN ISO 6892-1 standard?

The UNI EN ISO 6892-1 standard standardizes tensile tests on metals to obtain reliable and internationally comparable characteristic values of strength and strain.

How is tensile strength measured?

Tensile strength is measured by applying an increasing force on a sample until it breaks, determining the maximum load the material can withstand.

What are the advantages of using optical extensometers?

Optical extensometers offer precise and reliable measurements without physical contact with the sample, improving the accuracy of tests.

How does test speed affect the results?

Test speed affects the strength and deformation values of materials. Higher strain rates tend to produce higher strength values.



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