Elongation at break is one of the most fundamental mechanical properties measured in materials testing, quantifying how far a material can stretch before it fractures. In China, this test is governed by a well-established family of national standards (GB standards) covering plastics, rubber, textiles, metals, films, and wire and cable products. This guide explains the applicable GB standards, specimen preparation, test procedures, calculation methods, and practical applications to help manufacturers and laboratories achieve accurate and compliant test results.
Technical Overview
Elongation at break, designated as Eb in polymer testing and A in metallic tensile testing, is defined as the increase in the distance between gauge marks on a test specimen at the moment of rupture, expressed as a percentage of the original gauge length. It is a direct indicator of material ductility, flexibility, and process consistency. The property is calculated as follows: Eb (%) = (Lb − L0) / L0 × 100, where L0 is the original gauge length and Lb is the gauge length at break.
Chinese national standards are prefixed with GB (Guobiao), where GB indicates a mandatory standard and GB/T indicates a recommended national standard. Most elongation at break test methods are technically harmonized with corresponding ISO or IEC international standards, allowing test data generated under GB methods to be widely accepted for product certification, supplier qualification, and international trade documentation.
- GB/T 1040.1 — Plastics, determination of tensile properties, general principles (aligned with ISO 527-1)
- GB/T 1040.2 — Plastics, test conditions for moulding and extrusion plastics (aligned with ISO 527-2)
- GB/T 1040.3 — Plastics, test conditions for films and sheets (aligned with ISO 527-3)
- GB/T 528-2009 — Vulcanized or thermoplastic rubber, determination of tensile stress-strain properties (aligned with ISO 37)
- GB/T 3923.1-2013 — Textiles, tensile properties of fabrics, strip method (aligned with ISO 13934-1)
- GB/T 14337 and GB/T 14344 — Tensile properties of chemical fibers, staple fibers and filament yarns
- GB/T 228.1-2021 — Metallic materials, tensile testing at ambient temperature, percentage elongation after fracture (aligned with ISO 6892-1)
- GB/T 2951.11-2008 — Tensile strength and elongation at break of cable insulation and sheath compounds (aligned with IEC 60811)
- GB/T 8804 — Determination of tensile properties of thermoplastics pipes
The tests are performed on a universal tensile testing machine with a force measurement accuracy of class 1 or better, verified in accordance with GB/T 16825.1 or ISO 7500-1. Extension may be measured with contact or non-contact extensometers meeting GB/T 12160 requirements, or from crosshead displacement where the relevant standard permits it. While ASTM D638, ASTM D412, and ISO 527 are often referenced globally, GB/T methods are mandatory or preferred references for products sold in the Chinese market and for CCC-related product conformity assessments.
Testing Samples
Plastic Moulding and Extrusion Specimens (GB/T 1040.1 / GB/T 1040.2)
Rigid and semi-rigid plastics are tested using machined or moulded dumbbell specimens, most commonly type 1A and type 1B with a gauge length of 50 mm and a preferred thickness between 1 mm and 4 mm. Smaller type 5A and miniature specimens are available when full-size samples cannot be obtained, such as when cutting from finished parts. Rigid sheets may also be tested as parallel-sided strips when a valid dumbbell cannot be prepared.
Film and Sheet Specimens (GB/T 1040.3)
Plastic films below approximately 1 mm thickness are tested using small dumbbell specimens or rectangular strips with parallel edges cut carefully to avoid nicks that cause premature failure. For highly extensible films, the initial distance between grips is often used as the reference length. Test direction must be recorded separately for machine direction and transverse direction specimens, as elongation behavior is frequently anisotropic.
Rubber Specimens (GB/T 528)
Vulcanized and thermoplastic rubbers are tested using punched dumbbell specimens. Type 1 is the preferred specimen, featuring a gauge length of 25 mm, a width of 6 mm, and a preferred thickness of 2 mm. Types 2, 3, and 4 are used for thinner or smaller articles, and ring specimens may be used where specified by the product standard. Specimens must be punched with a sharp die to ensure clean, perpendicular edges.
Textile Specimens (GB/T 3923.1)
Woven and knitted fabrics are tested as cut strips 50 mm wide, or ravel-strip specimens prepared from wider cuts, with a gauge length of 200 mm (100 mm for narrow fabrics). Specimens are taken in warp and weft directions as required, and fringe-type edge damage must be avoided during preparation.
Chemical Fiber Specimens (GB/T 14337 / GB/T 14344)
Staple fibers are tested as individual fibers or bundle specimens, while filament yarns are tested on precision winders and pre-tensioned grips. Gauge lengths and pre-tension values are specified according to fiber type and linear density.
Wire and Cable Specimens (GB/T 2951.11)
Insulation and sheath compounds are sampled from finished cables, prepared as dumbbell specimens or tubular sections, and marked with a 20 mm gauge length. Elongation at break of insulation and sheath materials is a mandatory delivery test item in most wire and cable product standards.
Specimen Conditioning
Prior to testing, plastics are conditioned at 23 °C ± 2 °C and 50 % ± 10 % relative humidity in accordance with GB/T 2918, typically for at least 24 hours. Rubber is conditioned per GB/T 2941 for a minimum of 16 hours after vulcanization. Textiles are conditioned per GB/T 6529 at 20 °C ± 2 °C and 65 % ± 4 % relative humidity until moisture equilibrium is reached. Deviations from standard atmospheres must be reported.
Testing Items
Although elongation at break is frequently tested as a standalone parameter, national standards define it within a complete tensile stress-strain evaluation. Typical reported items include:
- Elongation at break (Eb or A), the percentage extension at rupture
- Tensile strength and tensile stress at break
- Tensile stress at yield and elongation at yield for ductile plastics
- Tensile stress at 100 %, 200 %, and 300 % elongation for rubber compounds
- Tensile modulus, including the 1 % secant modulus for plastics
- Force at break and force at yield
- Failure mode and break location, used to judge specimen validity
Testing Methods
The general test sequence under GB national standards is as follows:
- Prepare specimens according to the applicable product standard and condition them in the specified standard atmosphere.
- Measure thickness and width at the gauge marks with suitable instruments; reject specimens with dimension deviations beyond tolerance.
- Apply gauge marks accurately with a marking device or use the extensometer reference length.
- Mount the specimen in the grips with correct alignment and apply any specified pre-tension.
- Select the crosshead speed specified by the standard or the material specification.
- Run the test to rupture while recording the complete force-extension curve.
- Calculate elongation at break as (Lb − L0) / L0 × 100 %.
- Repeat on the required number of specimens, discard invalid breaks per the standard, and report the statistical result.
Typical Test Conditions by Material
- Plastics: 1 mm/min for modulus determination; commonly 50 mm/min for strength and elongation of type 1A/1B dumbbells, unless the material standard states otherwise.
- Rubber: 500 mm/min for type 1, 2, and 3 dumbbells; elongation is commonly tracked from grip separation or non-contact video extensometry because rupture extensions can exceed 600 %.
- Textiles: 20 mm/min when elongation at break does not exceed 75 %, and 100 mm/min when it exceeds 75 %, with a 200 mm gauge length.
- Metals: strain-rate-controlled testing with extensometers; elongation after fracture is measured on the reassembled specimen or by extensometer over the original gauge length.
Data Evaluation and Validity
A minimum of five valid specimens is generally required. Rubber results are reported as the median, while plastic and textile results are reported as the arithmetic mean, usually with the standard deviation. Specimens that break in the grips or outside the gauge marks are typically invalid and must be replaced unless break behavior is explicitly documented. Test reports must identify the standard, specimen type and dimensions, test speed, atmosphere, individual and statistical results, and any deviations, so that results remain traceable and defensible.
Applications
Elongation at break testing to GB national standards supports quality control, product certification, and materials research across virtually every manufacturing sector:
- Incoming inspection of polymer resins, compounds, and rubber batches before processing
- Factory quality control and delivery inspection of plastic films, sheets, and injection-moulded components
- Mandatory conformity testing of wire and cable insulation and sheath materials
- Verification of rubber seals, hoses, conveyor belts, and elastomeric components
- Textile and garment fabric performance evaluation in warp and weft directions
- Construction materials such as waterproofing membranes and geosynthetics
- Medical device components including tubing, films, and gloves
- Durability research, where elongation at break is a highly sensitive indicator of thermal aging, UV weathering, hydrolysis, and chemical exposure
- Supplier qualification, lot acceptance, and independent verification by accredited third-party laboratories for import and export trade
FAQ
What is elongation at break and why is it important?
Elongation at break is the percentage increase in gauge length that a material sustains before fracturing. It quantifies ductility and flexibility, and because it responds strongly to degradation, processing defects, and formulation changes, it is widely used as a sensitive quality and durability indicator.
Which national standard should I use for my material?
Use GB/T 1040 series for plastics and films, GB/T 528 for vulcanized or thermoplastic rubber, GB/T 3923.1 for woven and knitted fabrics, GB/T 14337 and GB/T 14344 for chemical fibers, GB/T 228.1 for metallic materials, and GB/T 2951.11 for cable insulation and sheaths. Product-specific standards may designate which method applies.
How many specimens are required for a valid test?
Most GB tensile standards require at least five valid specimens per condition or direction. Specimens that fail outside the gauge length or in the grips are treated as invalid and additional specimens must be tested.
Why do different laboratories sometimes report different values?
Variations arise from specimen preparation quality, conditioning history, crosshead speed, grip alignment and slippage, and whether extension is measured by extensometer or crosshead displacement. Strict adherence to the specified GB method and calibrated equipment is essential for reproducibility.
What are typical elongation at break values for common materials?
Representative ranges include 300 % to 700 % for soft rubber compounds, 200 % to 600 % for polyethylene films, 10 % to 300 % for common thermoplastics depending on grade, and values below 5 % for many rigid engineering plastics and metals. Always confirm against the specification of the specific material grade.
Are GB test results accepted internationally?
Because most GB tensile methods are aligned with the corresponding ISO or IEC standards, results from ISO/IEC 17025-accredited laboratories are generally accepted in international trade, though customers should confirm which method edition is required by their specifications.