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Home >> Application >> By Standard >> ISO >> ISO 5000~9999 >> ISO 9856 Conveyor belt - Tensile Test of Elastic Modulus and Permanent Elongation

ISO 9856 Conveyor belt - Tensile Test of Elastic Modulus and Permanent Elongation

ISO 9856 — Conveyor Belts: Determination of Elastic & Permanent Elongation and Calculation of Elastic Modulus

ISO 9856 specifies a laboratory method for determining the elastic elongation, permanent (non-recoverable) elongation, and elastic modulus of a conveyor belt's tensile member (fabric carcass or steel cord reinforcement) under cyclic loading.

A conveyor belt stretches in two ways — elastically (it springs back) and permanently (it stays longer, like a worn rubber band). ISO 9856 measures both, after the belt has been "worked in" with 200 load cycles, so engineers can properly size the take-up device, predict belt tracking behavior, and calculate safe transition distances on idlers.

Core Test Principle

A test piece is cut from the full thickness of the conveyor belt in the longitudinal direction (parallel to belt travel / along the reinforcement cords or fabric weave).

The test piece is mounted in a dynamic tensile testing machine and subjected to a cyclically varying tensile force that oscillates (approximately sinusoidally) between two reference force levels:

Symbol	Definition	Value
T	Nominal (specified minimum) tensile strength of the belt	N/mm of belt width
F_U (Upper reference force)	10 % of T	N/mm × test piece width
F_L (Lower reference force)	2 % of T	N/mm × test piece width
ΔF	Specific force range = F_U− F_L	N/mm

The cycling runs at 0.1 Hz (one cycle every 10 seconds) for 200 cycles.

After the 200th cycle, the force–elongation graph is read to extract:

Δle — the elastic (recoverable) elongation corresponding to ΔF

Δlp — the permanent (non-recoverable) elongation accumulated after cycling

From these, percentage strains and the elastic modulus M are calculated.

Test Specimen Requirement:

Sampling Rule: Sample must be taken no less than 5 full days after belt production vulcanization per ISO282 sampling regulation; prepare total three specimens: one from left edge, one from central area, one from right edge of full belt width.

Specimen Dimension: 50 mm width × minimum 300 mm free clamping length + extra end clamping allowance; full original belt thickness; all cut strictly along belt longitudinal direction;

Surface pre-treatment: Trim outer top/bottom rubber cover to retain residual thickness between 0.5 mm ~1.0 mm on specimen surface before testing.

ISO 9856 Conveyor belts Elongatio and Elastic Modulus Test Equipment

Cylic Tensile testing machine	Force calibration complies with ISO 7500‑1; load range covers minimum full nominal breaking load of tested belt; runs sinusoidal cyclic pulling.
Precision extensometer	Measuring length ≥ 100 mm; accuracy 0.1 mm or better. Two grids positioned on the test piece axis to track actual elongation (not just crosshead movement).
Recording system	Graphically records applied tensile force (N/mm) as a function of actual elongation — at minimum, the 1st and 200th cycles must be captured.

Cylic Tensile testing machine

Force calibration complies with ISO 7500‑1; load range covers minimum full nominal breaking load of tested belt; runs sinusoidal cyclic pulling.

Precision extensometer

Measuring length ≥ 100 mm; accuracy 0.1 mm or better.

Two grids positioned on the test piece axis to track actual elongation (not just crosshead movement).

Recording system

Graphically records applied tensile force (N/mm) as a function of actual elongation — at minimum, the 1st and 200th cycles must be captured.

ISO 9856 Conveyor belt - Tensile Test of Elastic Modulus and Permanent Elongation

Test Parameters

Parameter	Prescribed Value
Lower reference force, F_L	2 % of T (N/mm × 50 mm width)
Upper reference force, F_U	10 % of T (N/mm × 50 mm width)
Cycling waveform	Approximately sinusoidal
Frequency	0.1 Hz (= one cycle every 10 s)
Total cycles	200
Initial pre-load (before cycling)	0.5 % of T × test piece width
Free length between jaw faces	≥ 300 mm
Extensometer reference length	≥ 100 mm
Sample age before test	≥ 5 days after manufacture

Step by step Test procedure of ISO 9856 Tensile Test of Elastic Modulus and Permanent Elongation for Conveyor belt

Step 1 — Mount the Test Piece	Secure the ends of the test piece in the machine's jaws/clamps so it's held firmly. Verify the free (ungripped) length between the jaw faces is ≥ 300 mm.
Step 2 — Apply Pre-Load & Set Zero	Apply an initial (pre-) force = 0.5 % of T × test piece width. Position the extensometer grids on the test piece axis with a known reference length l₀ of ≥ 100 mm. Set the graphical recorder to zero elongation at this pre-loaded state.
Step 3 — Cyclic Loading	Program/operate the machine to apply force approximately sinusoidally oscillating between: FL (2% of T) ←→ FU (10% of T) Run at 0.1 Hz for 200 complete cycles. The recorder must capture the force–elongation curve for at least the 1st cycle and the 200th cycle.
Step 4 — Read the 200th-Cycle Graph	From 200th-cycle plotted curve: read elastic elongation Δle (length difference between upper/lower load) and permanent residual elongation Δlp (zero-load leftover extension);
Step 5 — Calculation and Test Report	Standard reference: ISO 9856; Complete unique identification information of tested conveyor belt (model, batch, specification, manufacturer); Individual test values of three specimens plus averaged final results for elastic strain, permanent strain and elastic modulus; Specimen conditioning period, standard conditioning atmosphere parameters, actual lab ambient temperature & RH during testing;

Target Application Industry Fields

Conveyor Belt Manufacturing: Incoming raw carcass material QC, finished heavy-duty belt factory outgoing inspection for coal, mineral, cement bulk transport belts;

Mining, Power Plant, Cement & Port Terminals: New belt incoming acceptance inspection and periodic performance evaluation of in-service running conveyor belts;

Third-party certification & inspection labs: International commodity certification, cross-border customs inspection, mine safety certification testing;

Rubber & textile carcass R&D institutes: New reinforcement fabric, rubber compound development to optimize belt stretch performance;

Conveyor engineering design firms: Parameter input for conveyor take-up stroke design (ISO 3870) and idler transition layout calculation (ISO 5293).

Related Test Standard:

GBT 15902	Conveyor belts — Determination of elastic and permanent elongation and calculation of elastic modulus.
ISO 7622-1	Steel cord conveyor belts - Longitudinal traction test - Part 1: Measurement of elongation
ISO 7622-2	Steel cord conveyor belts — Longitudinal traction test — Part 2: Measurement of tensile strength
ISO 283	Belt-specific adhesion or elongation tests
ISO 36	Vulcanized/thermoplastic rubber – Adhesion test between rubber and textile fabric

Related products and device

ISO 9856 Steel Cord Conveyor belts Adhesion peeling universal testing machine

WDW Series Computer Control Electronic Universal Testing Machine made by UNITEDTEST range from 100N to 600KN load capacity with various models like single columns, table type, door frame type etc., is used to perform tension, compression, flexure/bending, shearing, peeling etc., test for metal and nonmetal specimens.

ISO 9856 Conveyor belts Tensile test fixture

T-Peel Resistance Test Fixture for Adhesives is based on ASTM D1876 standard, used to measure the adhesion strength of adhesive maeterial. ASTM D1876 peel strength test method is commonly used to measure the strength of adhesive bonds between two sealed materials.

Conveyor belt tensile test fixture

Webbing test fixture used for tensile testing of the webbing, belt test sample, determine the webbing, belt tensile strength, elongation etc., Webbing is a strong fabric woven as a flat strip or tube of varying width and fibres often used in place of rope.

ISO 9856 long travel extension extensometer

High Elongation Extensometer is mainly used together with the tensile test machine for the rubber tension testing. It can measure the elongation of the product with high precision and accurately capture the displacement data. With a deformation measurement range typically from 10mm to 800mm.

Related Standard

ASTM D6775 Tensile Test Textile Webbing, Tape, Belt –

ASTM D6775 specifies how to determine breaking strength and optionally elongation at a specified force (EASF) of textile webbing, tape, and braided materials, using a split-drum type clamping assembly in a tensile testing machine.

ASTM D5035 Breaking Force and Elongation testing of Textile Fabrics (Strip Method) –

ASTM D5035 : Standard Test Method for Breaking Force and Elongation of Textile Fabrics (Strip Method)

ASTM D5035 is the standard test method for determining breaking force (tensile strength) and elongation at break of textile fabrics using the strip method. It defines two core procedures--raveled strip (for woven fabrics) and cut strip (for nonwovens, coated/felted fabrics)--and supports both dry and wet testing.

ASTM D5034 Grab Tensile Testing for Textile Fabrics Breaking Strength and Elongation –

ASTM D5034 for determining the breaking strength (maximum force a fabric can withstand before rupture) and elongation (amount of stretch under tension) of textile fabrics using the grab test principle. It provides two primary procedures: the grab test and modified grab test, with provisions for both dry and wet testing conditions.

ISO 283 Textile conveyor belts tensile and elongation test –

ISO 283 is the core tensile test standard for textile-reinforced conveyor belts. It specifies how to cut a full-thickness test piece from the belt and pull it in uniaxial tension until rupture, to determine the Full-thickness tensile strength, Elongation at break, Elongation at the reference force (load).

ISO 505 Tear propagation resistance test of textile conveyor belts –

ISO 505 specifying a universal tensile test method to quantify the tear propagation resistance of textile carcass conveyor belts, tested either at full belt thickness or stripped carcass-only condition, targeting belts prone to dangerous longitudinal splitting in service.

ISO 36 Rubber plastic peeling test of adhesion strength to textile fabrics –

ISO 36 defines the standardized 180° peel adhesion test to quantify bonding strength between vulcanized/thermoplastic rubber and textile fabrics via stripping separation force measurement. Tells you how strongly the rubber is glued/chemically bonded to the fabric.

FAQs for ISO 9856 Conveyor Belt Elongation Test

Q1: What is ISO 9856?

A: ISO 9856:2016 is an international standard titled “Conveyor belts — Determination of elastic and permanent elongation and calculation of elastic modulus.”It specifies a method to measure how much a conveyor belt stretches elastically (recoverable) and permanently (non‑recoverable) under cyclic loading, and calculates its elastic modulus (stiffness per unit width).

Q2: Why is this test important?

A: Conveyor belts stretch in two ways:

Elastic elongation affects troughing shape, transition curves, and dynamic tension.

Permanent elongation determines how much take‑up travel is needed to prevent slack.

ISO 9856 quantifies both after a “running‑in” phase (200 cycles), providing data essential for system design, procurement specs, and quality control. Without it, engineers would only know break strength, not real‑world elongation behavior.

Q3: Which conveyor belts does ISO 9856 apply to?

A: It applies to all heavy conveyor belts with textile or steel cord reinforcements. It is explicitly not applicable to light conveyor belts as defined in ISO 21183‑1.

Q4: What does the test actually measure?

A: The test measures:

Permanent elongation (Δlₚ): Non‑recoverable length increase after 200 load cycles.

Elastic elongation (Δlₑ): Recoverable stretch when the load changes between two reference forces.

Elastic modulus (M): Stiffness of the belt’s tensile member, expressed in N/mm of belt width (not N/mm²).

Q5: How are results calculated?

A:Permanent strain: εperm= (Δlp/ l0) × 100 [%]

Elastic strain: εelast= (Δle/ l0) × 100 [%]

Elastic modulus: M = (ΔF × l0) / Δle[N/mm of belt width]

where ΔF = FU− FLand l0is the extensometer gauge length.

The arithmetic mean of the three specimens is reported, rounded to one decimal place.

Q6: What is the difference between elastic and permanent elongation?

A:Elastic elongation is reversible—the belt returns to its original length when the load is removed.

Permanent elongation is irreversible—the belt stays longer even after unloading. Think of a rubber band that snaps back (elastic) versus one that stays stretched out (permanent).

Q7: What is the elastic modulus in ISO 9856, and how does it differ from Young’s modulus?

A: ISO 9856 defines elastic modulus M as force per unit belt width divided by strain (units: N/mm). This differs from classical Young’s modulus (E), which is stress (force per area) divided by strain (units: N/mm²). ISO 9856 uses belt‑width‑based stiffness because conveyor belts are specified by force‑per‑width, not stress.

Q8: How many test specimens are required, and where are they taken from?

A: Three specimens are required: one from each edge of the belt and one from the middle. This ensures representation across the belt’s width, as elongation can vary.

Q9: Why is the test performed after 200 load cycles?

A: A new belt undergoes most of its permanent stretch during initial use as fibers/cords seat into the rubber and internal structures settle. The 200‑cycle conditioning simulates this running‑in phase, giving elongation values representative of the belt’s working condition, not its fresh state.

Q10: Can ISO 9856 be used for light conveyor belts?

A: No. The standard explicitly excludes light conveyor belts covered by ISO 21183‑1. Light belts have different construction and elongation behavior, requiring separate test methods.

Q11: What is the significance of the 2% and 10% reference forces?

A: These percentages of the belt’s nominal tensile strength (T) define the force range used in cycling. They represent typical operating loads well below break strength, ensuring the test reflects real‑world service conditions without damaging the belt.

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