ISO 527-1 – General Principles of Plastics Tensile Testing

Overview & scope

ISO 527-1 is the international "general principles" standard for determining the tensile properties of plastics and plastic composites under defined conditions. It is maintained by ISO/TC 61 and acts as the pillar of the entire ISO 527 family — it sets the common rules (definitions, gauge length, speed, conditioning, modulus calculation) that Parts 2 to 5 then apply to specific material classes. In India it is adopted verbatim by the Bureau of Indian Standards as IS 13360-5-1.

The standard defines how to derive tensile strength, tensile modulus, yield stress, and elongation from a controlled stress–strain test, and is the default tensile reference for plastics compounders, moulders, masterbatch producers, and NABL / ISO 17025-accredited laboratories across India and worldwide.

Tip: ISO 527-1 is the framework, not a stand-alone test method. Always pair it with the part that matches your material — Part 2 for moulding and extrusion plastics, Part 3 for films and sheets, Parts 4 and 5 for composites.

What does it measure?

Tensile strength (MPa), tensile stress at yield and at break (MPa), tensile modulus of elasticity (MPa or GPa), nominal strain and percent elongation at yield and break, and Poisson's ratio when biaxial extensometry is used. It does not cover flexural, impact, or rheological behaviour — see ISO 178, ISO 179/180, and ISO 1133 respectively.

Sample materials

Rigid and semi-rigid thermoplastic moulding and extrusion compounds (PP, PE, ABS, PC, PA6/PA66, POM, PET, PBT), filled and reinforced grades, thermosetting moulding materials, sheets and laminates, and fibre-reinforced thermoset and thermoplastic composites — including recycled and compounded grades for QC.

What it excludes

ISO 527-1 is not normally suitable for rigid cellular materials (use ISO 1926) or for sandwich structures containing cellular cores. Confirm the current edition on iso.org and the part cited in your customer specification.

Industries & applications

The ISO 527 family & specimens

ISO 527-1 itself defines the principles of the specimen — shape requirements, dimensional measurement accuracy, permitted tolerances, and the initial gauge length — but the actual specimen geometries live in the application parts. Choosing the right part is the first decision in any ISO 527 test.

Tip: The ISO 3167 Type 1A multipurpose specimen (gauge length 50 mm, 10 mm wide, 4 mm thick) is the workhorse for moulding compounds under Part 2 — always state the specimen type and part in the report.

Specimen preparation & conditioning

1. Prepare specimens by injection moulding (Type 1A) to the cavity dimensions of the chosen part, or machine them (Type 1B) from sheet with smooth, defect-free edges.
2. Inspect for sink marks, voids, flash, and weld lines in the gauge section — discard any specimen with visible defects.
3. Condition at 23°C ± 2°C and 50% ± 5% RH per ISO 291 for the time required by the material standard (commonly a minimum of 16–88 hours depending on material).
4. Measure width and thickness of the narrow section at several points with a calibrated micrometer to the accuracy required by ISO 527-1; use the minimum cross-sectional area for stress.
5. Mark the gauge length for extensometer placement, avoiding scoring the specimen surface.

Grip selection

• Wedge-action or pneumatic grips with serrated or rubber-faced jaws suit most rigid plastics; match jaw inserts to specimen thickness.
• Align the specimen on the load axis to avoid bending stresses that cause premature shoulder failures.
• For reinforced or high-strength compounds and composite coupons, use higher-capacity grips and end tabs, and confirm no slippage with pre-marked references.
• Discard results where the specimen breaks inside the grip or at the tab radius rather than the gauge section.

Instrumentation & extensometry

• Extensometer is mandatory for modulus. ISO 527-1 derives the tensile modulus over a defined low-strain window, so crosshead displacement alone is not acceptable — machine and grip compliance distort low-strain data.
• Use a clip-on contact extensometer or a non-contact video extensometer for delicate, thin-film, or notch-sensitive materials.
• Select a load cell so peak force falls between 10% and 90% of rated capacity for best resolution.
• Sample at a sufficient data rate to resolve the linear region; increase for brittle materials that fail abruptly.

Test procedure

1. Record temperature, humidity, and specimen identification for the batch.
2. Verify current load cell and extensometer calibration; zero both channels.
3. Mount the specimen squarely in both grips, aligned to the load axis without pre-stress.
4. Attach or enable the extensometer at the marked gauge length.
5. Run the modulus segment at the low speed (typically 1 mm/min), then continue to strength and break at the higher speed required by the part.
6. Acquire the full force–extension curve to break; reject any specimen failing in the grip or tab radius and repeat on a fresh specimen.
7. Export tensile strength, modulus, yield, and elongation with the curve for traceability.

Calculations & reported values

Example: an ISO 3167 Type 1A specimen with width 10.0 mm and thickness 4.0 mm has A₀ = 40.0 mm². At a peak force of 2,000 N, tensile strength σ_m = 2000 / 40.0 = 50 MPa.

Speed of testing

• 1 mm/min — standard speed for the tensile modulus segment (corresponds to a strain rate of about 0.87%/min on a 50 mm gauge).
• 5 mm/min and 50 mm/min — common speeds for strength and elongation on rigid and ductile materials respectively.
• 0.125 to 500 mm/min — the full range of standardised speeds in ISO 527-1 Table 1; always follow the governing material or OEM specification and document the speed.

Tip: Plastics are strain-rate sensitive — reporting a result without the test speed makes it impossible to compare across labs. ISO 527 allows a speed change after modulus is captured, so log both speeds.

Reporting requirements

• Reference to ISO 527-1 and the application part used (e.g. ISO 527-2), plus material identification, grade, and lot/batch number.
• Specimen type, individual dimensions, cross-sectional area, and number tested (with any rejected specimens and reasons).
• Conditioning per ISO 291, test temperature and humidity, both test speeds, grip type, and extensometer type / gauge length.
• Results with statistics: tensile strength, modulus, yield stress, strain/elongation (mean, SD, CV%).

ISO 527 vs ASTM D638 — key differences

Both standards measure tensile properties of plastics but use different specimen geometries, modulus definitions, and speeds, so results are not directly numerically comparable. Select the standard cited by your customer or target market.

Tip: If a specification simply says "tensile test," confirm ISO 527 or ASTM D638 before moulding specimens — the dumbbell geometries differ and archived data will not be comparable.

Recommended Testometric setup

Model suggestions for plastics

Specifications vary by configuration; contact FITCO India for a tuned method and accessories aligned to ISO 527.

FAQs