Tensile test on plastics according to ISO 527 and ASTM D638

The tensile test according to ISO 527 or ASTM D638 is used to determine the mechanical tensile properties of plastics and plastic composite materials under defined test conditions. Among other things, tensile strength, modulus of elasticity, tensile stress, ultimate stress, and elongation at fracture are determined. The resulting stress-strain curve provides information on how a plastic deforms under tensile load and when the material fails.

The inspekt duo 10 kN universal testing machine from Hegewald & Peschke is suitable for performing such tests and can be adapted to the specific test task using various grips and strain measurement systems.

What is examined in a tensile test according to ISO 527?

In a plastic tensile test, a defined test specimen is subjected to axial loading. During the test, force and elongation are continuously recorded. Various mechanical properties of the material can be determined from these measured values.

The most important properties include: Depending on the test task, additional properties can be determined from the stress-strain diagram, such as Poisson’s ratio.

• Tensile strength: the maximum mechanical tensile stress that a material can withstand
• Modulus of elasticity (E-modulus): A material property that, under linear-elastic behavior, describes the proportional relationship between stress and strain that occurs when a solid body is deformed.
• Yield stress: The first local maximum stress in the stress-strain diagram—an increase in strain without an increase in stress
• Ultimate stress: Tensile stress that occurs when the test specimen breaks
• Elongation at fracture: Percentage of permanent elongation of the tensile specimen (relative to the initial measured length) after specimen failure
• Poisson’s ratio (coefficient of transverse contraction): A material property that describes the ratio of the relative change in thickness to the relative change in length in a uniaxial tensile test.

ISO 527-1 and ISO 527-2

The ISO 527 series of standards describes the determination of the tensile properties of plastics.

ISO 527-1 specifies the general principles of testing. These include, among other things, the general requirements for conducting the test and determining the tensile properties.

Test conditions for different material groups are specified in subsequent parts of the standard:

ISO 527-2: Molding and extrusion compounds
ISO 527-3: Thin films and sheets with a thickness < 1 mm
ISO 527-4: Isotropic and anisotropic fiber-reinforced plastic composites
ISO 527-5: Unidirectional fiber-reinforced plastic composites

The current edition of ISO 527-2 was published in 2025 and replaces the previous edition from 2012. It covers the test conditions for molded and extruded plastics and refers, among other things, to ISO 20753 regarding test specimens.

Tensile Testing of Plastics According to ASTM D638

In addition to ISO 527, tensile tests on plastics can also be performed according to ASTM D638. The standard specifies the determination of tensile properties of unreinforced and reinforced plastics using standardized dumbbell shaped specimens under defined test conditions. The method is commonly used for material characterization, quality control, specification and research and development.

As with ISO 527, the test is performed using a universal testing machine. The specimen is clamped in suitable grips and subjected to a defined tensile load while force and specimen deformation are recorded. Depending on the test setup and material, tensile strength, elongation and tensile modulus can be determined.

ASTM D638 covers different specimen geometries and materials with thicknesses up to 14 mm. For thin plastic sheeting and films below 1 mm thickness, ASTM D882 is generally the preferred test method.

The inspekt duo universal testing machine can be configured for tensile testing according to ASTM D638 with suitable grips, extensometers and test software. This allows the testing system to be adapted to different specimen geometries, materials and testing requirements.

ASTM D638 and ISO 527

ASTM D638 and ISO 527 address the same general subject, the determination of tensile properties of plastics, but they differ in their technical requirements and test procedures. Therefore, test results obtained according to the two standards should not automatically be considered directly equivalent.

How is a plastic tensile test conducted?

For the tensile test, a suitable test specimen is clamped into the grips of the universal testing machine. It is important to ensure axial and reproducible clamping as much as possible so that lateral loads or misalignment do not influence the test results.

The test specimen is then loaded at the speed specified for the respective test. The testing machine records the applied force and the change in length of the test specimen.

The stress-strain curve is generated from the measurement data. This curve is used to determine the characteristic values relevant to the respective test.

For plastics with high elongations, suitable strain measurement is particularly important. In contrast, determining the tensile modulus requires measuring very small changes in length, which is why a correspondingly precise measurement is necessary. ISO 527-1 specifies special requirements for this.

Testing Machine for Plastic Tensile Tests

The inspekt duo 10 kN is designed for versatile tensile and compression tests and can be equipped with various components for plastic tensile testing.

Pneumatic grips

Pneumatic grips can be used for plastic specimens. The clamping pressure can be controlled and adjusted. This ensures reproducible test conditions and enables the testing of thin and force-sensitive specimens.

Force-holding mode

During clamping, undesirable compressive stresses can arise, particularly with sensitive plastic specimens. The inspekt duo therefore features a force-holding mode that can be used to reduce these effects.

This is particularly useful for sensitive films or fiber-reinforced plastics, for example.

Specimen Depth Stops

Specimen depth stops enable reproducible positioning of the specimen in the grips. This promotes as axial a clamping as possible and reduces the influence of lateral loads on the test result.

Strain Measurement with the MFE910-1

For plastic tensile tests, the inspekt duo can be combined with the long-distance extensometer MFE910-1.

The inductive fine-measurement range enables the determination of elastic properties such as the modulus of elasticity in accordance with Method B of ISO 527-1. Thanks to the long measurement stroke, additional parameters such as the equivalent proof strength, proof strength, and elongation at fracture can also be determined for plastics and elastomers with high elongation.

Test Specimens for Plastic Tensile Tests

Defined test specimens are used for tests according to ISO 527. Depending on the material, manufacturing process, and test method, different specimen shapes are used.

Hegewald & Peschke offers various specimen punches, cutting presses, and cutting tools for the production of suitable plastic test specimens.

This allows the testing process to be coordinated from specimen preparation through to mechanical testing.

LabMaster Testing Software

The universal testing machine can be operated directly via the manual control panel on the machine or via the LabMaster testing software.

In LabMaster, test parameters for different specimen shapes and materials can be stored. The test sequence can thus be defined, carried out, and evaluated. The measured force and strain values are then available for evaluating the relevant properties and the stress-strain curve.

Conducting Reproducible Plastic Tensile Tests

Meaningful and comparable test results depend on more than just the force measurement of the testing machine. The specimen geometry, clamping, strain measurement, test parameters, and evaluation must also be coordinated.

The inspekt duo can therefore be equipped with various grips, strain measurement systems, and other components depending on the test task.

This results in a testing system that can be adapted to different plastics, specimen shapes, and test requirements.

Frequently Asked Questions About the Plastic Tensile Test According to ISO 527

What is determined during a tensile test according to ISO 527?

The tensile test can be used to determine, among other things, tensile strength, modulus of elasticity, tensile stress, tensile strength at break, and elongation at fracture of plastics.

What is the difference between ISO 527-1 and ISO 527-2?

ISO 527-1 describes the general principles for determining tensile properties. ISO 527-2 specifies the specific test conditions for molded and extruded plastics.

Which testing machine is suitable for plastic tensile tests?

For plastic tensile tests, universal testing machines are used, which enable suitable force measurement, appropriate grips, and strain measurement tailored to the test task.

What type of strain measurement is required for plastic tensile testing?

That depends on the test method and the material. Determining the modulus of elasticity requires particularly precise measurements of small changes in length. For materials with large strains, however, a correspondingly long measurement stroke is required. The inspekt duo, for example, can be equipped with the MFE910-1 long-distance extensometer for this purpose.

Your testing system for plastic tensile tests

Universal testing machine: inspekt duo 10 kN
Grips: pneumatic grips
Strain measurement: MFE910-1
Testing software: LabMaster
Testing standards: ISO 527 or ASTM D638

The combination of testing machine, gripping technology, strain measurement, software, and test methods enables reproducible testing of a wide variety of plastic specimens.

About the inspekt duo universal testing machine

About pneumatic grips for plastic testing

About the MFE910-1 long-distance extensometer

About the LabMaster testing software

About sample punching and cutting presses

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