Tensile test on plastics according to ISO 527: Requirements and test conditions
ISO 527 is a Internationally recognized standard for determining the mechanical properties of plastics under tensile stressIt describes standardized testing procedures to To determine key parameters such as tensile strength, modulus of elasticity and elongation.
Key facts at a glance
ISO 527 regulates the Tensile test on plastics to determine mechanical properties such as tensile strength, modulus of elasticity and elongation. It creates a uniform basis for reproducible results in quality assurance, goods receipt and material development.
Key contents of the standard:
- Testing of unreinforced, filled and fiber-reinforced plastics
- Standard parts 1 to 4 for different material forms
- Defined sample geometries such as type 1A and 1B
- Fixed test speeds and conditioning
- Calibration requirements for force and strain measurement
What does the DIN EN ISO 527 standard regulate?
The DIN EN ISO 527 series of standards describes the performance of tensile tests on plastics in order to determine mechanical properties such as tensile strength, elongation and modulus of elasticity. The goal is to obtain reproducible results that allow for the comparison of different materials or batches. – regardless of the testing laboratory, the user, or the location. ISO 527 is therefore a key standard for material characterization in plastics engineering.
The series of standards is divided into several parts with specific areas of application:
- ISO 527-1 specifies the general principles of testing. These include specimen shapes, testing speed, gauge lengths, tolerances, and environmental requirements.
- ISO 527-2 contains supplementary specifications for molding and extrusion compounds that are typically in injection-molded or pressed form.
- ISO 527-3 applies to thin films and sheets with a thickness of less than 1 mm.
- ISO 527-4 refers to multidirectional, long fiber reinforced plastics, for example in automotive or aerospace engineering.
- ISO 527-5 covers the testing of unidirectional fiber-reinforced plastic composites, e.g., spars, reinforcement profiles, aircraft wings.
In practice, the standard is particularly relevant in the Quality assurance, incoming goods inspection and materials development for use. Aging tests and media storage tests can also be carried out using ISO 527 to evaluate material changes under environmental or temperature influences in accordance with standards. Therefore, the tensile test according to ISO 527 is not suitable for component design, but very well suited for material comparison, production control, and research and development.
Standard parts at a glance: ISO 527-1 to ISO 527-4 explained briefly
ISO 527 is divided into several parts, covering different material types and test conditions. The following overview shows the essential content of each part of the standard:
| Standard parts | Title | Application |
|---|---|---|
| ISO 527-1 | General principles | Definition of terms, sample shapes, test parameters and measurement methods for tensile testing of plastics |
| ISO 527-2 | Test conditions for molding and extrusion compounds | Specifications for solid plastics such as injection-molded or pressed specimens, type 1A and 1B |
| ISO 527-3 | Testing conditions for films and boards | Applies to thin plastic films under 1 mm and flat sheets. |
| ISO 527-4 | Test conditions for long fiber reinforced plastics | Testing of fiber-reinforced thermoplastics for structural components |
| ISO 527-5 | Test conditions for long fiber reinforced plastics | Testing of unidirectional fiber-reinforced plastic composites for lightweight construction and high-strength structural components |
This structure enables a targeted selection of the relevant standard, depending on material type, sample shape, and test objective. All components are based on the principle of comparability and define clearly measurable parameters under standardized conditions.
Test conditions and sample requirements according to ISO 527-1/-2
ISO 527-1 and ISO 527-2 define the technical parameters for tensile tests on plastics with a thickness greater than 1 mm. The aim is to ensure the highest possible comparability of results – even between different laboratories and machines. To this end, the standard specifies precise requirements for specimen geometry, gauge lengths, tolerances, environmental conditions, and the test procedure.
Sample shapes and measuring lengths
The standard distinguishes two preferred sample shapes for solid plastics:
- Type 1A: Injection molded, preferably for comparative studies
- Type 1B: mechanically machined or milled from pressed plates
Both sample types have a tapered measuring range. The measuring length is typically 75 mm (alternatively 50 mm). The clamping length is 115 mm. The sample width within the measuring range is 10 mm, and the thickness is 4 mm ± 0,2 mm.
Tolerances and accuracy requirements
The dimensions of the test specimens must be within tight tolerances to ensure precise results. Even slight deviations, especially in specimen thickness, can significantly distort the stress values. ISO 527 refers to ISO 16012 or ASTM D5947 for dimensional determination and specifies particular requirements for measuring instruments and measuring forces depending on the specimen type.
Particularly high accuracy requirements apply to the measurement of the tensile modulus. Annex C of ISO 527-1 specifies that the change in length in this area must be determined with an accuracy of ± 1% over the defined modulus measurement length. This requires high-resolution strain measurement systems (e.g., extensometers or optical systems) with a minimum resolution of 100%. >1µm.
Conditioning and environment
Samples must be stored in a standard climate for at least 16 hours before testing. The standard climate is 23 ± 2 °C and 50 ± 10% relative humidity (according to ISO 291). Different requirements apply to special cases – for example, weathered or chemically aged plastics. ISO 527 also allows the use of special sample shapes (e.g., type CW/CP) for aging tests with a reduced cross-section.
Test speed and preload
The standard specifies a defined testing speed, depending on the desired evaluation (e.g., tensile strength, elongation, modulus). A low preload during clamping ensures standardized contact with the testing machine. The testing speed significantly influences the result, especially with viscoelastic materials, and should be adhered to precisely.
Stress-strain diagram according to ISO 527
Legend and classification of the diagram
X-axis: Strain or nominal strain
Y-axis: tensile stress
The diagram shows typical stress-strain curves of different material types according to ISO 527.
Curve 1 – Brittle material
Fails at low elongation without a pronounced stretching phase. Typical for very stiff or glassy plastics.
Curves 2 and 3 – Materials with stretching behavior
Both show pronounced extension.
In curve 2, the stress continues to increase beyond the yield strength.
In curve 3, the tension remains almost constant after reaching the tensile strain.
Up to the point of elongation, the stress is measured in relation to the elongation; thereafter, it is measured in relation to the nominal elongation.
Curve 4 – Rubber-like material
Very high elongation at relatively low stress. Fracture often only occurs above 50% elongation.
Depending on the measurement technique, stress-strain or stress-nominal strain is displayed.
Important note: As soon as a tensile strain occurs, the strain measurement is no longer carried out via the extensometer with cutting edge distance L0 or Le, but via the clamping length L.
The shape of the tensile test specimen is crucial for reproducible test results. Type, dimensions, and requirements for clamping length or thickness are precisely defined.
Suitable testing machines for ISO 527
Testing machines for ISO 527 must meet high requirements for force measurement, strain measurement, and testing speed. Calibration according to ISO 7500-1, precisely controllable test sequences, and suitable clamping devices for Type 1A and Type 1B specimens are essential. Modern systems offer predefined ISO 527 test programs, digital extensometers, and automated evaluations for maximum reproducibility.
Tensile testing machines with these characteristics reliably meet the normative requirements for ISO 527-1 and ISO 527-2:
FAQ: Frequently asked questions about DIN EN ISO 527
Which test specimens should be used preferentially?
For comparable results, the standard recommends using Type 1A (injection-molded) or Type 1B (milled). Type 1A is generally preferable because it is more standardized.
How accurately must the strain be measured to determine the module?
The strain must be measured with an accuracy of ±1% over the defined module measuring section. This requires high-precision extensometers or optical systems.
Is the tensile test according to ISO 527 suitable for component evaluations?
Only to a limited extent. The results primarily serve for material comparison under laboratory conditions, not for the direct design of real components.
What is the difference between ISO 527 and ASTM D638?
Both standards test plastics in tensile tests, but differ in sample shape, test speed, and evaluation. Therefore, the results are not directly comparable.
