🔩 Tensile properties of plastics — tensile modulus determined between 0.05 % and 0.25 % strain
In short
The test specimen is extended along its longitudinal axis at a constant test speed until it breaks or until a specified value of stress or elongation is reached, while measuring the force and the elongation. The test is performed according to PN-EN ISO 527-1:2020-01; Modulus determination range: Between strains of 0.05 % and 0.25 %; chord modulus or slope of the least-squares line. The procedure comprises 8 steps; it is used for: Acceptance and quality control of thermoplastics and thermosets, Testing of plastic films, plates, sheets and laminates, Testing of composites reinforced with glass, carbon and aramid fibre.
At a glance
- Standard: PN-EN ISO 527-1:2020-01
- Category: Materials and NDT
- Procedure steps: 8
- Quantities determined: Tensile modulus, tensile strength, stress and strain at yield, stress and strain at break, stress at a specified strain
- Modulus determination range: Between strains of 0.05 % and 0.25 %; chord modulus or slope of the least-squares line
- Elongation accuracy for the modulus: For gauge lengths up to 50 mm — ±1 µm (change introduced in the 2019 edition)
Overview
The standard specifies the general principles for determining the tensile properties of plastics and plastic composites under defined conditions. Several types of test specimen are defined to suit different types of material; details are given in the subsequent parts of the ISO 527 series. The methods are used to investigate the tensile behaviour of the test specimens and to determine the tensile strength, the tensile modulus and other aspects of the tensile stress–strain relationship.
The methods are selectively suitable for: rigid and semi-rigid thermoplastic moulding, extrusion and cast materials, including filled and reinforced compounds, as well as sheets and films of these materials; rigid and semi-rigid thermosetting moulding materials, including filled and reinforced compounds, and sheets and laminates; fibre-reinforced thermosetting and thermoplastic composites incorporating unidirectional or non-unidirectional reinforcements such as mats, woven fabrics, woven rovings, chopped strands, combination and hybrid reinforcements, rovings and milled fibres, as well as sheets made from pre-impregnated materials (prepregs); and thermotropic liquid-crystal polymers. The methods are not normally suitable for rigid cellular materials, for which ISO 1926 is used, or for sandwich structures containing cellular materials.
The individual parts of the series specify the particular conditions: part 2 — for moulding and extrusion plastics, part 3 — for films and sheets with a thickness of less than 1 mm, part 4 — for isotropic and orthotropic fibre-reinforced composites, part 5 — for unidirectional fibre-reinforced composites. One test comprises at least five test specimens, and the final result for the property determined is their mean value. In the edition ISO 527-1:2019 an inconsistency concerning the accuracy of the elongation used to calculate the modulus was removed: for a gauge length of not more than 50 mm the accuracy was set at ±1 µm.
Method principle
The test specimen is extended along its major longitudinal axis at a constant test speed until it breaks or until the stress (load) or the strain (elongation) reaches a predetermined value. During the test the force sustained by the specimen and its elongation are measured. Stress is defined as the normal force related to the initial cross-sectional area within the gauge length, the cross-section being the product of the initial width and thickness of the central part of the specimen; to distinguish it from the true stress, related to the current cross-section, it is sometimes called the engineering stress. The test speed is the rate of separation of the grips. The tensile modulus is the slope of the stress–strain curve in the interval between strains of 0.05 % and 0.25 %; it may be calculated as a chord modulus or as the slope of a least-squares regression line.
Applications
- Acceptance and quality control of thermoplastics and thermosets
- Testing of plastic films, plates, sheets and laminates
- Testing of composites reinforced with glass, carbon and aramid fibre
- Comparison of raw material batches and assessment of the effect of fillers and reinforcements
- Input data for design calculations and material documentation
Key parameters
| Parameter | Value |
|---|---|
| Quantities determined | Tensile modulus, tensile strength, stress and strain at yield, stress and strain at break, stress at a specified strain |
| Modulus determination range | Between strains of 0.05 % and 0.25 %; chord modulus or slope of the least-squares line |
| Elongation accuracy for the modulus | For gauge lengths up to 50 mm — ±1 µm (change introduced in the 2019 edition) |
| Number of test specimens | At least five per test; the final result is the mean value |
| Geometric quantities | L0 — gauge length, b — width, h — thickness, A = b·h — initial cross-section |
| Test speed | Rate of separation of the grips, in mm/min; constant during the test |
| Exclusions | The methods are not normally suitable for rigid cellular materials (ISO 1926) or for sandwich structures with cellular materials |
Standard
- Standard number
- PN-EN ISO 527-1:2020-01
- Title (PL)
- Tworzywa sztuczne — Oznaczanie właściwości mechanicznych przy statycznym rozciąganiu — Część 1: Zasady ogólne
- Title (EN)
- Plastics — Determination of tensile properties — Part 1: General principles
Step-by-step procedure
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Preparation of test specimens
Mould the test specimens to the selected dimensions or machine, cut or punch them from finished and semi-finished products: mouldings, laminates, films and extruded or cast sheets. The types of test specimen and the method of their preparation are specified in the relevant parts of the ISO 527 series, selected according to the type of material.
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Measurement of dimensions
Measure the width b and the thickness h in the central part of the test specimen in accordance with ISO 16012 and calculate the initial cross-section A = b·h. Determine the gauge length L0 — the distance between the gauge marks on the central part of the specimen; the values given for the individual specimen types are maximum gauge lengths.
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Conditioning
Condition the test specimens in a standard atmosphere in accordance with ISO 291; for rubber-like materials the preparation and conditioning procedures according to ISO 23529 are used.
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Test conditions
Carry out the test in a test atmosphere in accordance with ISO 291. Check the calibration of the force measuring system (ISO 7500-1) and of the extensometer (ISO 9513), and when determining the modulus meet the calibration requirements of Annex C of the standard.
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Gripping the specimen and selecting the speed
Grip the test specimen axially, without pre-stress and without slippage. Select the test speed according to the relevant part of the series and the type of quantity determined; lower speeds are used for determining the modulus than for determining the strength.
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Extension
Extend the test specimen at a constant speed along its longitudinal axis until it breaks or until the specified value of stress or elongation is reached, recording the force and the elongation.
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Calculations
Calculate the stress as the quotient of the force and the initial cross-section, and the strain related to the gauge length. Determine the tensile modulus from the strain interval from 0.05 % to 0.25 %, as well as the tensile strength (stress at the first local maximum), the stress and strain at yield, and the stress and strain at break.
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Result and report
Test at least five test specimens and give the mean value; estimate the confidence interval for the mean in accordance with ISO 2602. In the report give the type and kind of test specimen, the conditioning and test conditions, the test speed and the quantities determined.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Tensile testing machine | With a force measuring system calibrated according to ISO 7500-1, with a constant, adjustable rate of separation of the grips | — |
| Extensometer | Elongation measuring system calibrated according to ISO 9513; calibration requirements for modulus determination are given in Annex C of the standard | — |
| Grips | Holding the test specimen without slippage and without damage in the gripping area | — |
| Dimension measuring instruments | Determination of the linear dimensions of test specimens in accordance with ISO 16012 | — |
| Climatic chamber for conditioning | Standard atmospheres for conditioning and testing according to ISO 291 | — |
| Cutting die or machine tool for test specimens | For punching, cutting or machining test specimens from finished products and semi-finished products | — |
Health and safety (OHS)
- Breaking of the test specimen releases elastic energy — guard around the working space of the machine, safety glasses
- Fragments on breaking of fibre-reinforced composites — guard, avoid contact with fibre fragments
- Punching and machining of test specimens — tool guards, extraction of plastic and composite dust
- Dust from glass and carbon composites irritates the skin and respiratory tract — gloves, mask, extraction
- Moving grips of the machine — do not reach between the grips during the test
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 527-1:2020-01 — “Plastics — Determination of tensile properties — Part 1: General principles”.
How does this method work?
The test specimen is extended along its major longitudinal axis at a constant test speed until it breaks or until the stress (load) or the strain (elongation) reaches a predetermined value. During the test the force sustained by the specimen and its elongation are measured.
What is the measuring range and accuracy?
Quantities determined: Tensile modulus, tensile strength, stress and strain at yield, stress and strain at break, stress at a specified strain; Modulus determination range: Between strains of 0.05 % and 0.25 %; chord modulus or slope of the least-squares line; Elongation accuracy for the modulus: For gauge lengths up to 50 mm — ±1 µm (change introduced in the 2019 edition); Number of test specimens: At least five per test; the final result is the mean value.
How long does the test take?
The procedure comprises 8 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Tensile testing machine, Extensometer, Grips, Dimension measuring instruments, Climatic chamber for conditioning, Cutting die or machine tool for test specimens.
Where is this test used?
Acceptance and quality control of thermoplastics and thermosets; Testing of plastic films, plates, sheets and laminates; Testing of composites reinforced with glass, carbon and aramid fibre; Comparison of raw material batches and assessment of the effect of fillers and reinforcements; Input data for design calculations and material documentation.
What safety precautions apply?
Breaking of the test specimen releases elastic energy — guard around the working space of the machine, safety glasses; Fragments on breaking of fibre-reinforced composites — guard, avoid contact with fibre fragments; Punching and machining of test specimens — tool guards, extraction of plastic and composite dust; Dust from glass and carbon composites irritates the skin and respiratory tract — gloves, mask, extraction; Moving grips of the machine — do not reach between the grips during the test.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 527-1.